TY - JOUR A1 - Arya, Pooja A1 - Feldmann, David A1 - Kopyshev, Alexey A1 - Lomadze, Nino A1 - Santer, Svetlana T1 - Light driven guided and self-organized motion of mesoporous colloidal particles JF - Soft matter N2 - We report on guided and self-organized motion of ensembles of mesoporous colloidal particles that can undergo dynamic aggregation or separation upon exposure to light. The forces on particles involve the phenomenon of light-driven diffusioosmosis (LDDO) and are hydrodynamic in nature. They can be made to act passively on the ensemble as a whole but also used to establish a mutual interaction between particles. The latter scenario requires a porous colloid morphology such that the particle can act as a source or sink of a photosensitive surfactant, which drives the LDDO process. The interplay between the two modes of operation leads to fascinating possibilities of dynamical organization and manipulation of colloidal ensembles adsorbed at solid-liquid interfaces. While the passive mode can be thought of to allow for a coarse structuring of a cloud of colloids, the inter-particle mode may be used to impose a fine structure on a 2D particle grid. Local flow is used to impose and tailor interparticle interactions allowing for much larger interaction distances that can be achieved with, e.g., DLVO type of forces, and is much more versatile. Y1 - 2019 U6 - https://doi.org/10.1039/c9sm02068c SN - 1744-683X SN - 1744-6848 VL - 16 IS - 5 SP - 1148 EP - 1155 PB - Royal Society of Chemistry CY - Cambridge ER - TY - JOUR A1 - Arya, Pooja A1 - Jelken, Joachim A1 - Feldmann, David A1 - Lomadze, Nino A1 - Santer, Svetlana T1 - Light driven diffusioosmotic repulsion and attraction of colloidal particles JF - The journal of chemical physics : bridges a gap between journals of physics and journals of chemistr N2 - In this paper, we introduce the phenomenon of light driven diffusioosmotic long-range attraction and repulsion of porous particles under irradiation with UV light. The change in the inter-particle interaction potential is governed by flow patterns generated around single colloids and results in reversible aggregation or separation of the mesoporous silica particles that are trapped at a solid surface. The range of the interaction potential extends to several times the diameter of the particle and can be adjusted by varying the light intensity. The "fuel" of the process is a photosensitive surfactant undergoing photo-isomerization from a more hydrophobic trans-state to a rather hydrophilic cis-state. The surfactant has different adsorption affinities to the particles depending on the isomerization state. The trans-isomer, for example, tends to accumulate in the negatively charged pores of the particles, while the cis-isomer prefers to remain in the solution. This implies that when under UV irradiation cis-isomers are being formed within the pores, they tend to diffuse out readily and generate an excess concentration near the colloid's outer surface, ultimately resulting in the initiation of diffusioosmotic flow. The direction of the flow depends strongly on the dynamic redistribution of the fraction of trans- and cis-isomers near the colloids due to different kinetics of photo-isomerization within the pores as compared to the bulk. The unique feature of the mechanism discussed in the paper is that the long-range mutual repulsion but also the attraction can be tuned by convenient external optical stimuli such as intensity so that a broad variety of experimental situations for manipulation of a particle ensemble can be realized. Y1 - 2020 U6 - https://doi.org/10.1063/5.0007556 SN - 0021-9606 SN - 1089-7690 VL - 152 IS - 19 PB - American Institute of Physics CY - Melville, NY ER - TY - JOUR A1 - Arya, Pooja A1 - Jelken, Joachim A1 - Lomadze, Nino A1 - Santer, Svetlana A1 - Bekir, Marek T1 - Kinetics of photo-isomerization of azobenzene containing surfactants JF - The journal of chemical physics : bridges a gap between journals of physics and journals of chemistry N2 - We report on photoisomerization kinetics of azobenzene containing surfactants in aqueous solution. The surfactant molecule consists of a positively charged trimethylammonium bromide head group, a hydrophobic spacer connecting via 6 to 10 CH2 groups to the azobenzene unit, and the hydrophobic tail of 1 and 3CH(2) groups. Under exposure to light, the azobenzene photoisomerizes from more stable trans- to metastable cis-state, which can be switched back either thermally in dark or by illumination with light of a longer wavelength. The surfactant isomerization is described by a kinetic model of a pseudo first order reaction approaching equilibrium, where the intensity controls the rate of isomerization until the equilibrated state. The rate constants of the trans-cis and cis-trans photoisomerization are calculated as a function of several parameters such as wavelength and intensity of light, the surfactant concentration, and the length of the hydrophobic tail. The thermal relaxation rate from cis- to trans-state is studied as well. The surfactant isomerization shows a different kinetic below and above the critical micellar concentration of the trans isomer due to steric hindrance within the densely packed micelle but does not depend on the spacer length. KW - genomic DNA conformation KW - water-interface KW - light photocontrol KW - driven KW - manipulation KW - photoisomerization KW - molecules Y1 - 2020 U6 - https://doi.org/10.1063/1.5135913 SN - 0021-9606 SN - 1089-7690 VL - 152 IS - 2 PB - American Institute of Physics CY - Melville ER - TY - JOUR A1 - Bekir, Marek A1 - Jelken, Joachim A1 - Jung, Se-Hyeong A1 - Pich, Andrij A1 - Pacholski, Claudia A1 - Kopyshev, Alexey A1 - Santer, Svetlana T1 - Dual responsiveness of microgels induced by single light stimulus JF - Applied physics letters N2 - We report on the multiple response of microgels triggered by a single optical stimulus. Under irradiation, the volume of the microgels is reversibly switched by more than 20 times. The irradiation initiates two different processes: photo-isomerization of the photo-sensitive surfactant, which forms a complex with the anionic microgel, rendering it photo-responsive; and local heating due to a thermo-plasmonic effect within the structured gold layer on which the microgel is deposited. The photo-responsivity is related to the reversible accommodation/release of the photo-sensitive surfactant depending on its photo-isomerization state, while the thermo-sensitivity is intrinsically built in. We show that under exposure to green light, the thermo-plasmonic effect generates a local hot spot in the gold layer, resulting in the shrinkage of the microgel. This process competes with the simultaneous photo-induced swelling. Depending on the position of the laser spot, the spatiotemporal control of reversible particle shrinking/swelling with a predefined extent on a per-second base can be implemented. Y1 - 2021 U6 - https://doi.org/10.1063/5.0036376 SN - 0003-6951 SN - 1077-3118 VL - 118 IS - 9 PB - American Institute of Physics CY - Melville ER - TY - JOUR A1 - Bekir, Marek A1 - Sharma, Anjali A1 - Umlandt, Maren A1 - Lomadze, Nino A1 - Santer, Svetlana T1 - How to make a surface act as a micropump JF - Advanced materials interfaces N2 - In this paper, the phenomenon of light-driven diffusioosmotic (DO) long-range attractive and repulsive interactions between micro-sized objects trapped near a solid wall is investigated. The range of the DO flow extends several times the size of microparticles and can be adjusted to point towards or away from the particle by varying irradiation parameters such as intensity or wavelength of light. The "fuel" of the light-driven DO flow is a photosensitive surfactant which can be photo-isomerized between trans and cis-states. The trans-isomer tends to accumulate at the interface, while the cis-isomer prefers to stay in solution. In combination with a dissimilar photo-isomerization rate at the interface and in bulk, this yields a concentration gradient of the isomers around single particles resulting in local light-driven diffusioosmotic (l-LDDO) flow. Here, the extended analysis of the l-LDDO flow as a function of irradiation parameters by introducing time-dependent development of the concentration excess of isomers near the particle surface is presented. It is also demonstrated that the l-LDDO can be generated at any solid/liquid interface being more pronounced in the case of strongly absorbing material. This phenomenon has plenty of potential applications since it makes any type of surface act as a micropump. KW - azobenzene containing surfactant KW - light-driven diffusioosmosis KW - rate of KW - photo-isomerization Y1 - 2022 U6 - https://doi.org/10.1002/admi.202102395 SN - 2196-7350 VL - 9 IS - 12 PB - Wiley-VCH CY - Weinheim ER - TY - JOUR A1 - Di Florio, G. A1 - Bruendermann, E. A1 - Yadavalli, Nataraja Sekhar A1 - Santer, Svetlana A1 - Havenith, Martina T1 - Graphene multilayer as nanosized optical strain gauge for polymer surface relief gratings JF - Nano letters : a journal dedicated to nanoscience and nanotechnology N2 - In this paper, we show how graphene can be utilized as a nanoscopic probe in order to characterize local opto-mechanical forces generated within photosensitive azobenzene containing polymer films. Upon irradiation with light interference patterns, photosensitive films deform according to the spatial intensity variation, leading to the formation of periodic topographies such as surface relief gratings (SRG). The mechanical driving forces inscribing a pattern into the films are supposedly fairly large, because the deformation takes place without photofluidization; the polymer is in a glassy state throughout. However, until now there has been no attempt to characterize these forces by any means. The challenge here is that the forces vary locally on a nanometer scale. Here, we propose to use Raman analysis of the stretching of the graphene layer adsorbed on top of polymer film under deformation in order to probe the strength of the material transport spatially resolved. With the well-known mechanical properties of graphene, we can obtain lower bounds on the forces acting within the film. Upon the basis of our experimental results, we can deduce that the internal pressure in the film due to grating formation can exceed 1 GPa. The graphene-based nanoscopic gauge opens new possibilities to characterize opto-mechanical forces generated within photosensitive polymer films. KW - Surface relief grating KW - optomechanical forces KW - photosensitive polymer films KW - multilayer graphene deformation KW - confocal Raman microscopy Y1 - 2014 U6 - https://doi.org/10.1021/nl502631s SN - 1530-6984 SN - 1530-6992 VL - 14 IS - 10 SP - 5754 EP - 5760 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Di Florio, G. A1 - Bruendermann, E. A1 - Yadavalli, Nataraja Sekhar A1 - Santer, Svetlana A1 - Havenith, Martina T1 - Confocal raman microscopy and AFM study of the interface between the photosensitive polymer layer and multilayer graphene JF - Soft materials N2 - In this paper we report on the interaction between photosensitive azobenzene-containing polymer films and on top adsorbed graphene multilayers. The photosensitive polymer film changes its topography under irradiation with light interference patterns according to their polarization distribution. The multilayer graphene follows the deformation of the polymer film and stretches accordingly. Using confocal Raman microspectroscopy we can detect the appearance of additional peaks in the Raman spectrum of the photosensitive polymer film upon irradiation indicating a molecular interaction at the interface between the graphene multilayer and the polymer matrix. Multi-component analysis of the specific Raman bands shows that the interaction involves the graphene rings and the aromatic rings of the azobenzenes causing the strong adhesion between the two materials. KW - Graphene KW - Multilayer graphene KW - Photosensitive polymer film KW - Confocal Raman microscopy KW - AFM KW - Surface Relief Grating KW - Interfacial molecular interaction Y1 - 2014 U6 - https://doi.org/10.1080/1539445X.2014.945040 SN - 1539-445X SN - 1539-4468 VL - 12 SP - S98 EP - S105 PB - Taylor & Francis Group CY - Philadelphia ER - TY - JOUR A1 - Di Florio, Giuseppe A1 - Bruendermann, Erik A1 - Yadavalli, Nataraja Sekhar A1 - Santer, Svetlana A1 - Havenith, Martina T1 - Polarized 3D Raman and nanoscale near-field optical microscopy of optically inscribed surface relief gratings: chromophore orientation in azo-doped polymer films JF - Soft matter N2 - We have used polarized confocal Raman microspectroscopy and scanning near-field optical microscopy with a resolution of 60 nm to characterize photoinscribed grating structures of azobenzene doped polymer films on a glass support. Polarized Raman microscopy allowed determining the reorientation of the chromophores as a function of the grating phase and penetration depth of the inscribing laser in three dimensions. We found periodic patterns, which are not restricted to the surface alone, but appear also well below the surface in the bulk of the material. Near-field optical microscopy with nanoscale resolution revealed lateral two-dimensional optical contrast, which is not observable by atomic force and Raman microscopy. Y1 - 2014 U6 - https://doi.org/10.1039/c3sm51787j SN - 1744-683X SN - 1744-6848 VL - 10 IS - 10 SP - 1544 EP - 1554 PB - Royal Society of Chemistry CY - Cambridge ER - TY - GEN A1 - Di Florio, Giuseppe A1 - Bründermann, Erik A1 - Yadavalli, Nataraja Sekhar A1 - Santer, Svetlana A1 - Havenith, Martina T1 - Polarized 3D Raman and nanoscale near-field optical microscopy of optically inscribed surface relief gratings BT - chromophore orientation in azo-doped polymer films N2 - We have used polarized confocal Raman microspectroscopy and scanning near-field optical microscopy with a resolution of 60 nm to characterize photoinscribed grating structures of azobenzene doped polymer films on a glass support. Polarized Raman microscopy allowed determining the reorientation of the chromophores as a function of the grating phase and penetration depth of the inscribing laser in three dimensions. We found periodic patterns, which are not restricted to the surface alone, but appear also well below the surface in the bulk of the material. Near-field optical microscopy with nanoscale resolution revealed lateral two-dimensional optical contrast, which is not observable by atomic force and Raman microscopy. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 247 KW - glass-transition temperature KW - holographic diffraction gratings KW - chain azobenzene polymers KW - molecular-reorientation KW - amorphous polymers KW - data-storage KW - thin-films KW - dye KW - photoisomerization KW - alignment Y1 - 2013 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-95233 SP - 1544 EP - 1554 ER - TY - JOUR A1 - DiFlorio, Giuseppe A1 - Bründermann, Erik A1 - Yadavall, Nataraja Sekhar A1 - Santer, Svetlana A1 - Havenith, Martina T1 - Polarized 3D Raman and nanoscale near-field optical microscopy of optically inscribed surface relief gratings: chromophore orientation in azo-doped polymer films N2 - We have used polarized confocal Raman microspectroscopy and scanning near-field optical microscopy with a resolution of 60 nm to characterize photoinscribed grating structures of azobenzene doped polymer films on a glass support. Polarized Raman microscopy allowed determining the reorientation of the chromophores as a function of the grating phase and penetration depth of the inscribing laser in three dimensions. We found periodic patterns, which are not restricted to the surface alone, but appear also well below the surface in the bulk of the material. Near-field optical microscopy with nanoscale resolution revealed lateral two-dimensional optical contrast, which is not observable by atomic force and Raman microscopy. Y1 - 2014 UR - http://pubs.rsc.org/en/content/articlepdf/2014/sm/c3sm51787j U6 - https://doi.org/10.1039/c3sm51787j SN - 1744-683x ER - TY - JOUR A1 - Feldmann, David A1 - Arya, Pooja A1 - Lomadze, Nino A1 - Kopyshev, Alexey A1 - Santer, Svetlana T1 - Light-driven motion of self-propelled porous Janus particles JF - Applied physics letters N2 - We introduce a versatile mechanism of light-driven self-propelled motion applied to porous Janus-type particles. The mechanism is based on the generation of local light-driven diffusio-osmotic (l-LDDO) flow around each single porous particle subjected to suitable irradiation conditions. The photosensitivity is introduced by a cationic azobenzene containing surfactant, which undergoes a photoisomerization reaction from a more hydrophobic trans-state to a rather hydrophilic cis-state under illumination with light. The negatively charged porous silica particles are dispersed in a corresponding aqueous solution and absorb molecules in their trans-state but expel them in their cis-state. During illumination with blue light triggering both trans-cis and cis-trans isomerization at the same time, the colloids start to move due to the generation of a steady-state diffusive flow of cis-isomers out of and trans-isomers into the particle. This is because a hemi-spherical metal cap partially sealing the colloid breaks the symmetry of the otherwise radially directed local flow around the particle, leading to self-propelled motion. Janus particles exhibit superdiffusive motion with a velocity of similar to 0.5 mu m/s and a persistence length of ca. 50 mu m, confined to microchannels the direction can be maintained up to 300 mu m before rotational diffusion reverts it. Particles forming dimers of different shapes can be made to travel along circular trajectories. The unique feature of this mechanism is that the strength of self-propulsion can be tuned by convenient external optical stimuli (intensity and irradiation wavelength) such that a broad variety of experimental situations can be realized in a spatiotemporal way and in situ. Y1 - 2019 U6 - https://doi.org/10.1063/1.5129238 SN - 0003-6951 SN - 1077-3118 VL - 115 IS - 26 PB - American Institute of Physics CY - Melville ER - TY - JOUR A1 - Feldmann, David A1 - Maduar, Salim R. A1 - Santer, Mark A1 - Lomadze, Nino A1 - Vinogradova, Olga I. A1 - Santer, Svetlana T1 - Manipulation of small particles at solid liquid interface: light driven diffusioosmosis JF - Scientific reports N2 - The strong adhesion of sub-micron sized particles to surfaces is a nuisance, both for removing contaminating colloids from surfaces and for conscious manipulation of particles to create and test novel micro/nano-scale assemblies. The obvious idea of using detergents to ease these processes suffers from a lack of control: the action of any conventional surface-modifying agent is immediate and global. With photosensitive azobenzene containing surfactants we overcome these limitations. Such photo-soaps contain optical switches (azobenzene molecules), which upon illumination with light of appropriate wavelength undergo reversible trans-cis photo-isomerization resulting in a subsequent change of the physico-chemical molecular properties. In this work we show that when a spatial gradient in the composition of trans-and cis-isomers is created near a solid-liquid interface, a substantial hydrodynamic flow can be initiated, the spatial extent of which can be set, e.g., by the shape of a laser spot. We propose the concept of light induced diffusioosmosis driving the flow, which can remove, gather or pattern a particle assembly at a solid-liquid interface. In other words, in addition to providing a soap we implement selectivity: particles are mobilized and moved at the time of illumination, and only across the illuminated area. Y1 - 2016 U6 - https://doi.org/10.1038/srep36443 SN - 2045-2322 VL - 6 SP - 25083 EP - 25091 PB - Nature Publ. Group CY - London ER - TY - JOUR A1 - Feldmann, David A1 - Maduar, Salim R. A1 - Santer, Mark A1 - Lomadze, Nino A1 - Vinogradova, Olga I. A1 - Santer, Svetlana T1 - Manipulation of small particles at solid liquid interface BT - light driven diffusioosmosis JF - Scientific reports N2 - The strong adhesion of sub-micron sized particles to surfaces is a nuisance, both for removing contaminating colloids from surfaces and for conscious manipulation of particles to create and test novel micro/nano-scale assemblies. The obvious idea of using detergents to ease these processes suffers from a lack of control: the action of any conventional surface-modifying agent is immediate and global. With photosensitive azobenzene containing surfactants we overcome these limitations. Such photo-soaps contain optical switches (azobenzene molecules), which upon illumination with light of appropriate wavelength undergo reversible trans-cis photo-isomerization resulting in a subsequent change of the physico-chemical molecular properties. In this work we show that when a spatial gradient in the composition of trans- and cis- isomers is created near a solid-liquid interface, a substantial hydrodynamic flow can be initiated, the spatial extent of which can be set, e.g., by the shape of a laser spot. We propose the concept of light induced diffusioosmosis driving the flow, which can remove, gather or pattern a particle assembly at a solid-liquid interface. In other words, in addition to providing a soap we implement selectivity: particles are mobilized and moved at the time of illumination, and only across the illuminated area. KW - genomic DNA conformation KW - photosensitive surfactants KW - optical manipulation KW - photocontrol KW - azobenzene KW - films KW - gradients KW - transport KW - tracking KW - brushes Y1 - 2016 U6 - https://doi.org/10.1038/srep36443 SN - 2045-2322 VL - 6 PB - Nature Publishing Group CY - London ER - TY - GEN A1 - Feldmann, David A1 - Maduar, Salim R. A1 - Santer, Mark A1 - Lomadze, Nino A1 - Vinogradova, Olga I. A1 - Santer, Svetlana T1 - Manipulation of small particles at solid liquid interface BT - light driven diffusioosmosis N2 - The strong adhesion of sub-micron sized particles to surfaces is a nuisance, both for removing contaminating colloids from surfaces and for conscious manipulation of particles to create and test novel micro/nano-scale assemblies. The obvious idea of using detergents to ease these processes suffers from a lack of control: the action of any conventional surface-modifying agent is immediate and global. With photosensitive azobenzene containing surfactants we overcome these limitations. Such photo-soaps contain optical switches (azobenzene molecules), which upon illumination with light of appropriate wavelength undergo reversible trans-cis photo-isomerization resulting in a subsequent change of the physico-chemical molecular properties. In this work we show that when a spatial gradient in the composition of trans- and cis- isomers is created near a solid-liquid interface, a substantial hydrodynamic flow can be initiated, the spatial extent of which can be set, e.g., by the shape of a laser spot. We propose the concept of light induced diffusioosmosis driving the flow, which can remove, gather or pattern a particle assembly at a solid-liquid interface. In other words, in addition to providing a soap we implement selectivity: particles are mobilized and moved at the time of illumination, and only across the illuminated area. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 293 KW - azobenzene KW - brushes KW - films KW - genomic DNA conformation KW - gradients KW - optical manipulation KW - photocontrol KW - photosensitive surfactants KW - tracking KW - transport Y1 - 2016 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-100338 ER - TY - JOUR A1 - Filimon, Marlena A1 - Kopf, Ilona A1 - Ballout, Fuad A1 - Schmidt, Dietrich A. A1 - Bruendermann, Erik A1 - Rühe, Jürgen A1 - Santer, Svetlana A1 - Havenith, Martina T1 - Smart polymer surfaces : mapping chemical landscapes on the nanometre scale N2 - We show that Scattering Infrared Near-field Microscopy (SNIM) allows chemical mapping of polymer monolayers that can serve as designed nanostructured surfaces with specific surface chemistry properties on a nm scale. Using s- SNIM a minimum volume of 100 nm x 100 nm x 15 nm is sufficient for a recording of a "chemical'' IR signature which corresponds to an enhancement of at least four orders of magnitudes compared to conventional FT-IR microscopy. We could prove that even in cases where it is essentially difficult to distinguish between distinct polymer compositions based solely on topography, nanophase separated polymers can be clearly distinguished according to their characteristic near-field IR response. Y1 - 2010 UR - http://www.rsc.org/Publishing/Journals/sm/index.asp U6 - https://doi.org/10.1039/C0sm00098a SN - 1744-683X ER - TY - JOUR A1 - Filimon, Marlena A1 - Kopf, Ilona A1 - Schmidt, Dietrich A. A1 - Bruendermann, Erik A1 - Rühe, Jürgen A1 - Santer, Svetlana A1 - Havenith, Martina T1 - Local chemical composition of nanophase-separated polymer brushes JF - Physical chemistry, chemical physics : a journal of European Chemical Societies N2 - Using scattering scanning nearfield infrared microscopy (s-SNIM), we have imaged the nanoscale phase separation of mixed polystyrene-poly(methyl methacrylate) (PS-PMMA) brushes and investigated changes in the top layer as a function of solvent exposure. We deduce that the top-layer of the mixed brushes is composed primarily of PMMA after exposure to acetone, while after exposure to toluene this changes to PS. Access to simultaneously measured topographic and chemical information allows direct correlation of the chemical morphology of the sample with topographic information. Our results demonstrate the potential of s-SNIM for chemical mapping based on distinct infrared absorption properties of polymers with a high spatial resolution of 80 nm x 80 nm. Y1 - 2011 U6 - https://doi.org/10.1039/c0cp02756a SN - 1463-9076 VL - 13 IS - 24 SP - 11620 EP - 11626 PB - Royal Society of Chemistry CY - Cambridge ER - TY - JOUR A1 - Frenkel, Mark A1 - Arya, Pooja A1 - Bormashenḳo, Edṿard A1 - Santer, Svetlana T1 - Quantification of ordering in active light driven colloids JF - Journal of colloid and interface science N2 - Hypothesis: Light driven diffusioosmosis allows for the controlled self-assembly of colloidal particles. Illuminating of colloidal suspensions built of nanoporous silica microspheres dispersed in aqueous solution containing photosensitive azobenzene cationic surfactant enables manufacturing self-assembled well-ordered 2D colloidal patterns. We conjectured that ordering in this patterns may be quantified with the Voronoi entropy. Experiments: Depending on the isomerization state the surfactant either tends to absorb (trans-state) into negatively charged pores or diffuse out (cis-isomer) of the particles generating an excess concentration near the colloids outer surface and thus resulting in the initiation of diffusioosmotic flow. The direction of the flow can be controlled by the wavelength and intensity of irradiation. Under irradiations with blue light the colloids separate within a few seconds forming equidistant particle ensemble where long range diffusioosmotic repulsion acts over distances exceeding several times the particle diameter. Hierarchy of ordering in the studied colloidal systems is distinguished, namely: i) ordering of individual separated colloidal particles; ii) ordering of clusters built of colloidal particles; iii) ordering within clusters of individual colloidal particles. Findings: The study of the temporal change in the Voronoi entropy for the light illuminated colloidal dispersions allowed quantification of ordering evolution on different lateral scales and under different irradiation conditions. Fourier analysis of the time evolution of the Voronoi entropy is presented. Fourier spectrum of the "small-area" (100 x 100 mu m) reveals the pronounced peak at f = 1.125 Hz reflecting the oscillations of individual particles at this frequency. Ordering in hierarchical colloidal system emerging on different lateral scales is addressed. The minimal Voronoi entropy is intrinsic for the close packed 2D clusters. (C) 2020 Published by Elsevier Inc. KW - Azobenzene containing cationic surfactants KW - Light induced diffusioosmotic flow KW - 2D colloid ordering KW - Voronoi entropy Y1 - 2021 U6 - https://doi.org/10.1016/j.jcis.2020.10.053 SN - 0021-9797 SN - 1095-7103 VL - 586 SP - 866 EP - 875 PB - Elsevier CY - San Diego ER - TY - JOUR A1 - Jelken, Joachim A1 - Henkel, Carsten A1 - Santer, Svetlana T1 - Polarization controlled fine structure of diffraction spots from an optically induced grating JF - Applied physics letters N2 - We report on the remote control of the fine structure of a diffraction spot from optically induced dual gratings within a photosensitive polymer film. The material contains azobenzene in the polymer side chains and develops a surface relief under two-beam holographic irradiation. The diffraction of a polarized probe beam is sensitive to the orientation of the azobenzene groups forming a permanently stored birefringence grating within the film. We demonstrate that the fine structure of the probe diffraction spot switches from a Gaussian to a hollow or a hollow to a "Saturn"-like structure by a change in polarization. This makes it potentially useful in photonic devices because the beam shape can be easily inverted by an external stimulus. Y1 - 2020 U6 - https://doi.org/10.1063/1.5140067 SN - 0003-6951 SN - 1077-3118 VL - 116 IS - 5 PB - American Institute of Physics CY - Melville ER - TY - JOUR A1 - Jelken, Joachim A1 - Henkel, Carsten A1 - Santer, Svetlana T1 - Solving an old puzzle: fine structure of diffraction spots from an azo-polymer surface relief grating JF - Applied physics : B, Lasers and optics N2 - We report on the experimental and theoretical interpretation of the diffraction of a probe beam during inscription of a surface relief grating with an interference pattern into a photo-responsive polymer film. For this, we developed a set-up allowing for the simultaneous recording of the diffraction efficiency (DE), the fine structure of the diffraction spot and the topographical changes, in situ and in real time while the film is irradiated. The time dependence of the DE, as the surface relief deepens, follows a Bessel function exhibiting maxima and minima. The size of the probe beam relative to the inscribed grating (i.e., to the size of the writing beams) matters and has to be considered for the interpretation of the DE signal. It is also at the origin of a fine structure within the diffraction spot where ring-shaped features appear once an irradiation time corresponding to the first maximum of the DE has been exceeded. Y1 - 2019 U6 - https://doi.org/10.1007/s00340-019-7331-8 SN - 0946-2171 SN - 1432-0649 VL - 125 IS - 11 PB - Springer CY - Heidelberg ER - TY - JOUR A1 - Jelken, Joachim A1 - Henkel, Carsten A1 - Santer, Svetlana T1 - Formation of half-period surface relief gratings in azobenzene containing polymer films JF - Applied physics : B, Lasers and optics N2 - We study the peculiar response of photo-sensitive polymer films irradiated with a certain type of interference pattern where one interfering beam is S-polarized, while the second one is P-polarized. The polymer film, although in a glassy state, deforms following the local polarization distribution of the incident light, and a surface relief grating (SRG) appears whose period is half the optical one. All other types of interference patterns result in the matching of both periods. The topographical response is triggered by the alignment of photo-responsive azobenzene containing polymer side chains orthogonal to the local electrical field, resulting in a bulk birefringence grating (BBG). We investigate the process of dual grating formation (SRG and BBG) in a polymer film utilizing a dedicated set-up that combines probe beam diffraction and atomic force microscopy (AFM) measurements, and permits acquiring in situ and in real-time information about changes in local topography and birefringence. We find that the SRG maxima appear at the positions of linearly polarized light (tilted by 45 degrees relative to the grating vector), causing the formation of the half-period topography. This permits to inscribe symmetric and asymmetric topography gratings with sub-wavelength period, while changing only slightly the polarization of one of the interfering beams. We demonstrate an easy generation of sawtooth profiles (blazed gratings) with adjustable shape. With these results, we have taken a significant step in understanding the photo-induced deformation of azo-polymer films. Y1 - 2020 U6 - https://doi.org/10.1007/s00340-020-07500-w SN - 0946-2171 SN - 1432-0649 VL - 126 IS - 9 PB - Springer CY - Heidelberg ER - TY - JOUR A1 - Jelken, Joachim A1 - Pandiyarajan, Chinnayan Kannan A1 - Genzer, Jan A1 - Lomadze, Nino A1 - Santer, Svetlana T1 - Fabrication of flexible hydrogel sheets featuring periodically spaced circular holes with continuously adjustable size in realtime JF - ACS applied materials & interfaces N2 - We report on the formation of stimuli-responsive structured hydrogel thin films whose pattern geometry can be adjusted on demand and tuned reversibly by varying solvent quality or by changing temperature. The hydrogel films, similar to 100 nm in thickness, were prepared by depositing layers of random copolymers comprising N-isopropylacrylamide and ultraviolet (UV)-active methacryloyloxybenzophenone units onto solid substrates. A two-beam interference pattern technique was used to cross-link the selected areas of the film; any unreacted material was extracted using ethanol after UV light-assisted cross-linking. In this way, we produced nanoholes, perfectly ordered structures with a narrow size distribution, negligible tortuosity, adjustable periodicity, and a high density. The diameter of the circular holes ranged from a few micrometers down to several tens of nanometers; the hole periodicity could be adjusted readily by changing the optical period of the UV interference pattern. The holes were reversibly closed and opened by swelling/deswelling the polymer networks in the presence of ethanol and water, respectively, at various temperatures. The reversible regulation of the hole diameter can be repeated many times within a few seconds. The hydrogel sheet with circular holes periodically arranged may also be transferred onto different substrates and be employed as tunable templates for the deposition of desired substances. KW - photosensitive polymers KW - PNIPAm KW - hydrogels KW - UV cross-linking KW - stimuli-responsive structured polymer films KW - azobenzene-containing molecules Y1 - 2018 U6 - https://doi.org/10.1021/acsami.8b09580 SN - 1944-8244 VL - 10 IS - 36 SP - 30844 EP - 30851 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Jelken, Joachim A1 - Santer, Svetlana T1 - Light induced reversible structuring of photosensitive polymer films JF - RSC Advances N2 - In this paper we report on photoswitchable polymer surfaces with dynamically and reversibly fluctuating topographies. It is well known that when azobenzene containing polymer films are irradiated with optical interference patterns the film topography changes to form a surface relief grating. In the simplest case, the film shape mimics the intensity distribution and deforms into a wave like, sinusoidal manner with amplitude that may be as large as the film thickness. This process takes place in the glassy state without photo-induced softening. Here we report on an intriguing discovery regarding the formation of reliefs under special illumination conditions. We have developed a novel setup combining the optical part for creating interference patterns, an AFM for in situ acquisition of topography changes and diffraction efficiency signal measurements. In this way we demonstrate that these gratings can be “set in motion” like water waves or dunes in the desert. We achieve this by applying repetitive polarization changes to the incoming interference pattern. Such light responsive surfaces represent the prerequisite for providing practical applications ranging from conveyer or transport systems for adsorbed liquid objects and colloidal particles to generation of adaptive and dynamic optical devices. KW - surface-relief gratings KW - induced deformation KW - mass-transport KW - azobenzene elastomers KW - thin-films KW - birefringence KW - roughness KW - network KW - erasure Y1 - 2019 U6 - https://doi.org/10.1039/C9RA02571E SN - 2046-2069 VL - 9 IS - 35 SP - 20295 EP - 20305 PB - RSC Publishing CY - London ER - TY - GEN A1 - Jelken, Joachim A1 - Santer, Svetlana T1 - Light induced reversible structuring of photosensitive polymer films T2 - Postprints der Universität Potsdam Mathematisch-Naturwissenschaftliche Reihe N2 - In this paper we report on photoswitchable polymer surfaces with dynamically and reversibly fluctuating topographies. It is well known that when azobenzene containing polymer films are irradiated with optical interference patterns the film topography changes to form a surface relief grating. In the simplest case, the film shape mimics the intensity distribution and deforms into a wave like, sinusoidal manner with amplitude that may be as large as the film thickness. This process takes place in the glassy state without photo-induced softening. Here we report on an intriguing discovery regarding the formation of reliefs under special illumination conditions. We have developed a novel setup combining the optical part for creating interference patterns, an AFM for in situ acquisition of topography changes and diffraction efficiency signal measurements. In this way we demonstrate that these gratings can be “set in motion” like water waves or dunes in the desert. We achieve this by applying repetitive polarization changes to the incoming interference pattern. Such light responsive surfaces represent the prerequisite for providing practical applications ranging from conveyer or transport systems for adsorbed liquid objects and colloidal particles to generation of adaptive and dynamic optical devices. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 750 KW - surface-relief gratings KW - induced deformation KW - mass-transport KW - azobenzene elastomers KW - thin-films KW - birefringence KW - roughness KW - network KW - erasure Y1 - 2019 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-436432 SN - 1866-8372 IS - 750 SP - 20295 EP - 20305 ER - TY - GEN A1 - Kasyanenko, Nina A1 - Unksov, Ivan A1 - Bakulev, Vladimir A1 - Santer, Svetlana T1 - DNA interaction with head-to-tail associates of cationic surfactants prevents formation of compact particles T2 - Postprints der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe N2 - Cationic azobenzene-containing surfactants are capable of condensing DNA in solution with formation of nanosized particles that can be employed in gene delivery. The ratio of surfactant/DNA concentration and solution ionic strength determines the result of DNA-surfactant interaction: Complexes with a micelle-like surfactant associates on DNA, which induces DNA shrinkage, DNA precipitation or DNA condensation with the emergence of nanosized particles. UV and fluorescence spectroscopy, low gradient viscometry and flow birefringence methods were employed to investigate DNA-surfactant and surfactant-surfactant interaction at different NaCl concentrations, [NaCl]. It was observed that [NaCl] (or the Debye screening radius) determines the surfactant-surfactant interaction in solutions without DNA. Monomers, micelles and non-micellar associates of azobenzene-containing surfactants with head-to-tail orientation of molecules were distinguished due to the features of their absorption spectra. The novel data enabled us to conclude that exactly the type of associates (together with the concentration of components) determines the result of DNA-surfactant interaction. Predomination of head-to-tail associates at 0.01 M < [NaCl] < 0.5 M induces DNA aggregation and in some cases DNA precipitation. High NaCl concentration (higher than 0.8 M) prevents electrostatic attraction of surfactants to DNA phosphates for complex formation. DAPI dye luminescence in solutions with DNA-surfactant complexes shows that surfactant tails overlap the DNA minor groove. The addition of di- and trivalent metal ions before and after the surfactant binding to DNA indicate that the bound surfactant molecules are located on DNA in islets T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 940 KW - azobenzene trimethylammonium bromide KW - head-to-tail surfactant associates KW - DNA KW - ionic strength KW - multivalent ions Y1 - 2020 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-459806 SN - 1866-8372 IS - 940 ER - TY - JOUR A1 - Kasyanenko, Nina A1 - Unksov, Ivan A1 - Bakulev, Vladimir A1 - Santer, Svetlana T1 - DNA interaction with head-to-tail associates of cationic surfactants prevents formation of compact particles JF - Molecules N2 - Cationic azobenzene-containing surfactants are capable of condensing DNA in solution with formation of nanosized particles that can be employed in gene delivery. The ratio of surfactant/DNA concentration and solution ionic strength determines the result of DNA-surfactant interaction: Complexes with a micelle-like surfactant associates on DNA, which induces DNA shrinkage, DNA precipitation or DNA condensation with the emergence of nanosized particles. UV and fluorescence spectroscopy, low gradient viscometry and flow birefringence methods were employed to investigate DNA-surfactant and surfactant-surfactant interaction at different NaCl concentrations, [NaCl]. It was observed that [NaCl] (or the Debye screening radius) determines the surfactant-surfactant interaction in solutions without DNA. Monomers, micelles and non-micellar associates of azobenzene-containing surfactants with head-to-tail orientation of molecules were distinguished due to the features of their absorption spectra. The novel data enabled us to conclude that exactly the type of associates (together with the concentration of components) determines the result of DNA-surfactant interaction. Predomination of head-to-tail associates at 0.01 M < [NaCl] < 0.5 M induces DNA aggregation and in some cases DNA precipitation. High NaCl concentration (higher than 0.8 M) prevents electrostatic attraction of surfactants to DNA phosphates for complex formation. DAPI dye luminescence in solutions with DNA-surfactant complexes shows that surfactant tails overlap the DNA minor groove. The addition of di- and trivalent metal ions before and after the surfactant binding to DNA indicate that the bound surfactant molecules are located on DNA in islets. KW - azobenzene trimethylammonium bromide KW - head-to-tail surfactant associates KW - DNA KW - ionic strength KW - multivalent ions Y1 - 2018 U6 - https://doi.org/10.3390/molecules23071576 SN - 1420-3049 VL - 23 IS - 7 PB - MDPI CY - Basel ER - TY - JOUR A1 - Koch, Markus A1 - Saphiannikova, Marina A1 - Santer, Svetlana A1 - Guskova, Olga T1 - Photoisomers of Azobenzene Star with a Flat Core: Theoretical Insights into Multiple States from DFT and MD Perspective JF - The journal of physical chemistry : B, Condensed matter, materials, surfaces, interfaces & biophysical chemistry N2 - This study focuses on comparing physical properties of photoisomers of an azobenzene star with benzene-1,3,5-tricarboxamide core. Three azobenzene arms of the molecule undergo a reversible trans-cis isomerization upon UV-vis light illumination giving rise to multiple states from the planar all-trans one, via two mixed states to the kinked all-cis isomer. Employing density functional theory, we characterize the structural and photophysical properties of each state indicating a role the planar core plays in the coupling between azobenzene chromophores. To characterize the light-triggered switching of solvophilicity/solvophobicity of the star, the difference in solvation free energy is calculated for the transfer of an azobenzene star from its gas phase to implicit or explicit solvents. For the latter case, classical all-atom molecular dynamics simulations of aqueous solutions of azobenzene star are performed employing the polymer consistent force field to shed light on the thermodynamics of explicit hydration as a function of the isomerization state and on the structuring of water around the star. From the analysis of two contributions to the free energy of hydration, the nonpolar van der Waals and the electrostatic terms, it is concluded that isomerization specificity largely determines the polarity of the molecule and the solute-solvent electrostatic interactions. This convertible hydrophilicity/hydrophobicity together with readjustable occupied volume and the surface area accessible to water, affects the self-assembly/disassembly of the azobenzene star with a flat core triggered by light. Y1 - 2017 U6 - https://doi.org/10.1021/acs.jpcb.7b07350 SN - 1520-6106 VL - 121 SP - 8854 EP - 8867 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Koenig, Tobias A1 - Goldenberg, Leonid M. A1 - Kulikovska, Olga A1 - Kulikovsky, Lazar A1 - Stumpe, Joachim A1 - Santer, Svetlana T1 - Reversible structuring of photosensitive polymer films by surface plasmon near field radiation JF - Soft matter N2 - We report on the fabrication and characterisation of a novel type of hybrid azo-modified photosensitive polymer film with a nanoscale metallic structuring integrated into the substrate. The metal structures permit to generate surface plasmon near fields when irradiated by UV-light from the rear without directly illuminating the polymer. This allows establishment of a localized, complex-shape intensity distribution at sub-wavelength resolution with a corresponding impact on the photosensitive polymer. The possibilities of exploiting this setup are manifold. We find that just by using the change of polarization of the incident light as means of control, the topography can be driven to change between various patterns reversibly. These results are confirmed by numerical simulations and compared with in situ recorded topography changes. Y1 - 2011 U6 - https://doi.org/10.1039/c0sm01164a SN - 1744-683X VL - 7 IS - 9 SP - 4174 EP - 4178 PB - Royal Society of Chemistry CY - Cambridge ER - TY - JOUR A1 - Koenig, Tobias A1 - Tsukruk, Vladimir V. A1 - Santer, Svetlana T1 - Controlled topography change of subdiffraction structures based on photosensitive polymer films induced by surface plasmon polaritons JF - ACS applied materials & interfaces N2 - We discuss the controlled subdiffraction modulations of photosensitive polymer films that are induced by surface plasmon interference in striking contrast to well-known conventional microscopic gratings. The near-field light intensity patterns were generated at the nanoslits fabricated in a silver layer with the photosensitive polymer film placed above. We observed that the topographical modulations can be excited only when the polarization is perpendicular to the nanoslits. Moreover, we have shown that light with certain wavelengths resulted in a characteristic topographical pattern with the periodicity three times smaller than the wavelength of incoming light. A combination of experimental observations with simulations showed that the unique subdiffraction topographical patterns are caused by constructive interference between two counter-propagating surface plasmon waves generated at neighboring nanoslits in the metal layer beneath the photosensitive polymer film. The light intensity distribution was simulated to demonstrate strong dependency upon the slit array periodicity as well as wavelength and polarization of incoming light. KW - azobenzene photosensitive polymer films KW - surface plasm on polaritons KW - silver nanoslits Y1 - 2013 U6 - https://doi.org/10.1021/am400712r SN - 1944-8244 VL - 5 IS - 13 SP - 6009 EP - 6016 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Kopyshev, Alexey A1 - Galvin, Casey J. A1 - Genzer, Jan A1 - Lomadze, Nino A1 - Santer, Svetlana T1 - Opto-mechanical scission of polymer chains in photosensitive diblock-copolymer brushes JF - Langmuir N2 - In this paper we report on an opto-mechanical scission of polymer chains within photosensitive diblock-copolymer brushes grafted to flat solid substrates. We employ surface-initiated polymerization of methylmethacrylate (MMA) and t-butyl methacrylate (tBMA) to grow diblock-copolymer brushes of poly(methylmethacrylate-b-t-butyl methacrylate) following the atom transfer polymerization (ATRP) scheme. After the synthesis, deprotection of the PtBMA block yields poly(methacrylic acid) (PMAA). To render PMMA-b-PMAA copolymers photosensitive, cationic azobenzene containing surfactants are attached to the negatively charged outer PMAA block. During irradiation with an ultraviolet (UV) interference pattern, the extent of photoisomerization of the azobenzene groups varies spatially and results in a topography change of the brush, i.e., formation of surface relief gratings (SRG). The SRG formation is accompanied by local rupturing of the polymer chains in areas from which the polymer material recedes. This opto-mechanically induced scission of the polymer chains takes place at the interfaces of the two blocks and depends strongly on the UV irradiation intensity. Our results indicate that this process may be explained by employing classical continuum fracture mechanics, which might be important for tailoring the phenomenon for applying it to poststructuring of polymer brushes. Y1 - 2013 U6 - https://doi.org/10.1021/la403241t SN - 0743-7463 VL - 29 IS - 45 SP - 13967 EP - 13974 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Kopyshev, Alexey A1 - Galvin, Casey J. A1 - Genzer, Jan A1 - Lomadze, Nino A1 - Santer, Svetlana T1 - Polymer brushes modified by photosensitive azobenzene containing polyamines JF - Polymer : the international journal for the science and technology of polymers N2 - This paper describes a strategy for preparing photosensitive polymeric grafts on flat solid surfaces by loading diblock-copolymer or homopolymer brushes with cationic azobenzene-containing surfactants. In contrast to previous work, we utilize photosensitive surfactants that bear positively-charged polyamine head groups whose charge varies between 1(+) and 3(+). Poly(methylmethacrylate-b-methacrylic acid) (PMMA-b-PMAA) brushes were prepared by employing atom transfer radical polymerization, where the bottom poly(methyl methacrylate) block was grown first followed by the synthesis of t-butyl methacrylate block that after de-protection yielded poly(methacrylic acid). We used PMMA-b-PMAA brushes with constant grafting density and length of the PMMA block, and three different lengths of the PMAA block. The azobenzene-based surfactants attached only to the PMAA block. The degree of binding (i.e., the number of surfactant molecules per binding site on the brush backbone) of the surfactants to the brush depends strongly on the valence of the surfactant head-group; within the brushes the concentration of the surfactant carrying unit charge is larger than that of multivalent surfactants. We detect pronounced response of the brush topography on irradiation with UV interference pattern even at very low degree of binding (as small as 0.08) of multi-valence surfactant. Areas on the sample that receive the highest UV dose exhibit chain scission. By removing the ruptured chains from the substrate via good solvent, one uncovers a surface topographical relief grating, whose spatial arrangement follows the intensity distribution of the UV light on the sample during irradiation. Due to strong coupling of the multi-valence surfactants to the polymer brush, it was possible in some cases to completely remove the polyelectrolyte block from the PMMA layer. The application of multi-valence azobenzene surfactants for triggering brush photosensitive has important advantage over usage of surfactant with unit charge because relative to single-valence surfactants much lower concentrations of the multivalent surfactant are needed to achieve comparable response upon UV irradiation. (C) 2016 Elsevier Ltd. All rights reserved. KW - Photosensitive brushes KW - Photosensitive azobenzene containing polyamines Y1 - 2016 U6 - https://doi.org/10.1016/j.polymer.2016.03.050 SN - 0032-3861 SN - 1873-2291 VL - 98 SP - 421 EP - 428 PB - Elsevier CY - Oxford ER - TY - JOUR A1 - Kopyshev, Alexey A1 - Galvin, Casey J. A1 - Patil, Rohan R. A1 - Genzer, Jan A1 - Lomadze, Nino A1 - Feldmann, David A1 - Zakrevski, Juri A1 - Santer, Svetlana T1 - Light-Induced Reversible Change of Roughness and Thickness of Photosensitive Polymer Brushes JF - Applied physics : A, Materials science & processing N2 - We investigate light-induced changes in thickness and roughness of photosensitive polymer brushes containing azobenzene cationic surfactants by atomic force microscopy (AFM) in real time during light irradiation. Because the cis-state of azobenzene unit requires more free volume than its trans counterpart, the UV light-induced expansion of polymer thin films associated with the trans-to-cis isomerism of azobenzene groups is expected to occur. This phenomenon is well documented in physisorbed polymer films containing azobenzene groups. In contrast, photosensitive polymer brushes show a decrease in thickness under UV irradiation. We have found that the azobenzene surfactants in their trans-state form aggregates within the brush. Under irradiation, the surfactants undergo photoisomerization to the cis-state, which is more hydrophilic. As a consequence, the aggregates within the brush are disrupted, and the polymer brush contracts. When subsequently irradiated with blue light the polymer brush thickness returns back to its initial value. This behavior is related to isomerization of the surfactant to the more hydrophobic trans-state and subsequent formation of surfactant aggregates within the polymer brush. The photomechanical function of the dry polymer brush, i.e., contraction and expansion, was found to be reversible with repeated irradiation cycles and requires only a few seconds for switching. In addition to the thickness change, the roughness of the brush also changes reversibly between a few Angstroms (blue light) and several nanometers (UV light). Photosensitive polymer brushes represent smart films with light responsive thickness and roughness that could be used for generating dynamic fluctuating surfaces, the function of which can be turned on and off in a controllable manner on a nanometer length scale. KW - photosensitive brushes KW - azobenzene containing surfactants KW - light driven reversible change of surface topography and thickness KW - domain memory in polymer brushes KW - orientation of azobenzenes in polymer brushes Y1 - 2016 U6 - https://doi.org/10.1021/acsami.6b06881 SN - 1944-8244 VL - 8 SP - 19175 EP - 19184 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Kopyshev, Alexey A1 - Kanevche, Katerina A1 - Lomadze, Nino A1 - Pfitzner, Emanuel A1 - Loebner, Sarah A1 - Patil, Rohan R. A1 - Genzer, Jan A1 - Heberle, Joachim A1 - Santer, Svetlana T1 - Light-Induced Structuring of Photosensitive Polymer Brushes JF - ACS Applied polymer materials N2 - We investigate light-induced irreversible structuring of surface topographies in poly(3-sulfopropyl methacrylate/potassium salt) (PSPMK) brushes on flat solid substrates prepared by surface-initiated atom transfer radical polymerization. The brushes have been loaded with azobenzene-based surfactant comprised of positively charged headgroups and hydrophobic tail. The surfactant exhibits photoresponsive properties through photoisomerization from the trans to cis states leading to significant changes in physicochemical properties of grafted polymer chains. The azobenzene surfactant enables photoresponsive behavior without introducing irreversible changes to chemical composition of the parent polymer brush. Exposing these photosensitive brushes to irradiation with UV interference beams causes the polymer brush to form surface relief grating (SRG) patterns. The cationic surfactant penetrates only similar to 25% of the upper portion of the PSPMK brush, resulting in the formation of two sections within the brush: a photoresponsive upper layer and nonfunctional buried layer, which is not affected by the UV irradiation. Using nano-FTIR spectroscopy, we characterize locally the chemical composition of the polymer brush and confirm partial penetration of the surfactant within the film. Strong optomechanical stresses take place only within the upper layer of the brush that is impregnated with the surfactants and causes surface topography alternation due to a local rupture of grafted polymer chains. The cleaved polymer chains are then removed from the surface by using a good solvent, leaving behind topographical grating on top of the nonfunctional brush layer. We demonstrate that photostructured polymer brush can be used for reversible switching of brush topography by varying external humidity. KW - photosensitive polymer brushes KW - reversible and irreversible structuring of polymer brushes KW - photosensitive azobenzene containing surfactant KW - strong polyelectrolyte brush KW - SRG formation in polymer brushes Y1 - 2019 U6 - https://doi.org/10.1021/acsapm.9b00705 SN - 2637-6105 VL - 1 IS - 11 SP - 301 EP - 3026 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Kopyshev, Alexey A1 - Lomadze, Nino A1 - Feldman, David A1 - Genzer, Jan A1 - Santer, Svetlana T1 - Making polymer brush photosensitive with azobenzene containing surfactants JF - Polymer : the international journal for the science and technology of polymers N2 - We report on rendering polyelectrolyte brushes photosensitive by loading them with azobenzene-containing cationic surfactants. Planar poly(methacrylic acid) (PMAA) brushes are synthesized using the “grafting from” free-radical polymerization scheme followed by exposure to a solution of photosensitive surfactants consisting of positively-charged head groups and hydrophobic tails into which azobenzene moieties are inserted. In this study the length of the hydrophobic methylene spacer connecting the azobenzene and the charged head group ranges from 4 to 10 CH2 groups. Under irradiation with UV light, the photo-isomerization of azobenzene integrated into a surfactant results in a change in size, geometry, dipole moment and free volume of the whole molecule. When the brush loaded with photosensitive surfactants is exposed to irradiation with UV interference patterns, the topography of the brush deforms following the distribution of the light intensity, exhibiting surface relief gratings (SRG). Since SRG formation is accompanied by a local rupturing of polymer chains in areas from which the polymer material is receding, most of the polymer material is removed from the surface during treatment with good solvent, leaving behind characteristic patterns of lines or dots. The azobenzene molecules still integrated within the polymer film can be removed by washing the brush with water. The remaining nano-structured brush can then be re-used for further functionalization. Although the opto-mechanically induced rupturing occurs for all surfactants, larger species do not penetrate deep enough into the brush such that after rupturing a leftover layer of polymer material remains on the substrate. This indicates that rupturing occurs predominantly in regions of high surfactant density. KW - Azobenzene containing cationic surfactants KW - Photosensitive polymer brushes KW - Opto-mechanically induced scission of polymer chains Y1 - 2015 U6 - https://doi.org/10.1016/j.polymer.2015.09.023 SN - 0032-3861 VL - 79 SP - 65 EP - 72 PB - Elsevier Science CY - Oxford ER - TY - JOUR A1 - Kopyshev, Alexey A1 - Lomadze, Nino A1 - Feldmann, David A1 - Genzer, Jan A1 - Santer, Svetlana T1 - Making polymer brush photosensitive with azobenzene containing surfactants JF - Polymer : the international journal for the science and technology of polymers N2 - We report on rendering polyelectrolyte brushes photosensitive by loading them with azobenzene-containing cationic surfactants. Planar poly( methacrylic acid) (PMAA) brushes are synthesized using the "grafting from" free-radical polymerization scheme followed by exposure to a solution of photosensitive surfactants consisting of positively-charged head groups and hydrophobic tails into which azobenzene moieties are inserted. In this study the length of the hydrophobic methylene spacer connecting the azobenzene and the charged head group ranges from 4 to 10 CH2 groups. Under irradiation with UV light, the photo-isomerization of azobenzene integrated into a surfactant results in a change in size, geometry, dipole moment and free volume of the whole molecule. When the brush loaded with photosensitive surfactants is exposed to irradiation with UV interference patterns, the topography of the brush deforms following the distribution of the light intensity, exhibiting surface relief gratings (SRG). Since SRG formation is accompanied by a local rupturing of polymer chains in areas from which the polymer material is receding, most of the polymer material is removed from the surface during treatment with good solvent, leaving behind characteristic patterns of lines or dots. The azobenzene molecules still integrated within the polymer film can be removed by washing the brush with water. The remaining nano-structured brush can then be re-used for further functionalization. Although the opto-mechanically induced rupturing occurs for all surfactants, larger species do not penetrate deep enough into the brush such that after rupturing a leftover layer of polymer material remains on the substrate. This indicates that rupturing occurs predominantly in regions of high surfactant density. KW - Azobenzene containing cationic surfactants KW - Photosensitive polymer brushes KW - Opto-mechanically induced scission of KW - polymer chains Y1 - 2015 U6 - https://doi.org/10.1016/j.polymer.2015.09.023 SN - 0032-3861 SN - 1873-2291 VL - 79 SP - 65 EP - 72 PB - Elsevier CY - Oxford ER - TY - JOUR A1 - König, Tobias A1 - Papke, Thomas A1 - Kopyshev, Alexey A1 - Santer, Svetlana T1 - Atomic force microscopy nanolithography fabrication of metallic nano-slits using silicon nitride tips JF - Journal of materials science N2 - In this paper, we report on the properties of nano-slits created in metal thin films using atomic force microscope (AFM) nanolithography (AFM-NL). We demonstrate that instead of expensive diamond AFM tips, it is also possible to use low cost silicon nitride tips. It is shown that depending on the direction of scratching, nano-slits of different widths and depths can be fabricated at constant load force. We elucidate the reasons for this behavior and identify an optimal direction and load force for scratching a gold layer. Y1 - 2013 U6 - https://doi.org/10.1007/s10853-013-7188-x SN - 0022-2461 VL - 48 IS - 10 SP - 3863 EP - 3869 PB - Springer CY - New York ER - TY - JOUR A1 - König, Tobias A1 - Santer, Svetlana T1 - Visualization of surface plasmon interference by imprinting intensity patterns on a photosensitive polymer JF - Nanotechnology N2 - We report on sub-wavelength structuring of photosensitive azo-containing polymer films induced by a surface plasmon interference intensity pattern. The two surface plasmon waves generated at neighboring nano-slits in the metal layer during irradiation interfere constructively, resulting in an intensity pattern with a periodicity three times smaller than the wavelength of the incoming light. The near field pattern interacts with the photosensitive polymer film placed above it, leading to a topography change which follows the intensity pattern exactly, resulting in the formation of surface relief gratings of a size below the diffraction limit. We analyze numerically and experimentally how the depth of the nano-slit alters the interference pattern of surface plasmons and find that the sub-wavelength patterning of the polymer surface could be optimized by modifying the geometry and the size of the nano-slit. Y1 - 2012 U6 - https://doi.org/10.1088/0957-4484/23/48/485304 SN - 0957-4484 VL - 23 IS - 48 PB - IOP Publ. Ltd. CY - Bristol ER - TY - JOUR A1 - König, Tobias A1 - Santer, Svetlana T1 - Stretching and distortion of a photosensitive polymer film by surface plasmon generated near fields in the vicinity of a nanometer sized metal pin hole JF - Nanotechnology N2 - Here we demonstrate how a surface plasmon (SP) generated near field pattern in the vicinity of a nano-scale pin hole can be used to generate reversible topography changes in a photosensitive polymer film above the opening. This can be achieved by simply changing the polarization state of the plasmon generating incoming light. In the case of linear polarization, the near field intensity pattern causes the film to laterally expand/contract according to the direction of the polarization. For circular polarization, two pronounced rims corresponding to maxima in the topography are observed. In all cases, the topographical variation is in close agreement with the SP intensity distribution computed from finite difference time domain simulation. Our results demonstrate the versatility of using SP near fields to imprint a variety of structures into photosensitive polymer films using only a single metallic mask. Y1 - 2012 U6 - https://doi.org/10.1088/0957-4484/23/15/155301 SN - 0957-4484 VL - 23 IS - 15 PB - IOP Publ. Ltd. CY - Bristol ER - TY - JOUR A1 - König, Tobias A1 - Sekhar, Y. Nataraja A1 - Santer, Svetlana T1 - Surface plasmon nanolithography impact of dynamically varying near-field boundary conditions at the air-polymer interface JF - Journal of materials chemistry N2 - It is well-known that surface plasmon generated near fields of suitably irradiated metal nano-structures can induce a patterning in an azobenzene-modified photosensitive polymer film placed on top. The change in the topography usually follows closely and permanently the underlying near field intensity pattern. With this approach, one can achieve a multitude of morphologies by additionally changing light intensity, polarization and the kind of metal used for nano-structuring. In this paper, we demonstrate that below a critical value of the polymer film thickness, the receding polymer material induces a change in refractive index of the glass-metal-polymer system, modifying the near field intensity distribution and causing a back-reaction on the flow of polymer material. This has a profound influence on the smallest size of topographical features that can be imprinted into the polymer. Y1 - 2012 U6 - https://doi.org/10.1039/c2jm15864g SN - 0959-9428 VL - 22 IS - 13 SP - 5945 EP - 5950 PB - Royal Society of Chemistry CY - Cambridge ER - TY - JOUR A1 - König, Tobias A1 - Yadavalli, Nataraja Sekhar A1 - Santer, Svetlana T1 - Near-Field induced reversible structuring of photosensitive polymer films Gold versus silver nano-antennas JF - Plasmonics N2 - We report on reversible structuring of photosensitive azo-containing polymer films induced by near-field intensity patterns emanating from illuminated nano-scale metal structures fabricated by colloidal lithography. Two different sets of these nano-antennas, consisting of either gold or silver, were investigated with respect to their ability to induce topography changes in a photosensitive polymer film placed above. Using in situ recorded atomic force microscopy micrographs of polymer topography changes during UV irradiation, we find that the response of the polymer film differs for the two metals at similar geometries of the metal nanostructures. The maximum topography change is stronger for Ag antennas as compared to the Au pattern, whereas the latter material revealed a pronounced splitting of topography maxima into two, a phenomenon less visible in the case of Ag. Finite difference time domain simulations of the electromagnetic field distribution in the vicinity of the metal structures confirm this remarkable observation. The local intensity is twice as large for the Ag as compared to the Au structures, and in each case, a splitting of the intensity pattern results, with a stronger modulation for Au. For both metals, the topography change was found to be reversible between a patterned and a flat by repeated change of irradiation conditions. KW - Photosensitive polymer films KW - Surface plasmons Y1 - 2012 U6 - https://doi.org/10.1007/s11468-012-9339-3 SN - 1557-1955 VL - 7 IS - 3 SP - 535 EP - 542 PB - Springer CY - New York ER - TY - JOUR A1 - Köpf, Michael H. A1 - Harder, Heiko A1 - Reiche, Jürgen A1 - Santer, Svetlana T1 - Impact of temperature on the LB patterning of DPPC on Mica JF - Langmuir N2 - The influence of the subphase temperature on the stripe pattern formation during Langmuir-Blodgett transfer (LB patterning) is investigated in a combined experimental and theoretical study. According to our experiments on the LB transfer of dipalmitoylphosphatidylcholine (DPPC) on planar mica substrates, even small temperature changes between 21.5 and 24.5 degrees C lead to significant changes in the monolayer patterns. For a constant surface pressure and dipper speed, the width of the stripes and the overall spatial period of the patterns increase with increasing subphase temperature. Because the stripe patterns are ascribed to alternating monolayer domains in the liquid-expanded and the liquid-condensed phases, the working regime for the formation of stripes is found to depend strongly on the respective surface pressure-area isotherm. These experimental findings are in accordance with the results of a theoretical investigation based on a model that takes hydrodynamics and the monolayer thermodynamics into account. Y1 - 2011 U6 - https://doi.org/10.1021/la202728t SN - 0743-7463 VL - 27 IS - 20 SP - 12354 EP - 12360 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Linde, Felix A1 - Yadavalli, Nataraja Sekhar A1 - Santer, Svetlana T1 - Conductivity behavior of very thin gold films ruptured by mass transport in photosensitive polymer film JF - APPLIED PHYSICS LETTERS N2 - We report on conductivity behavior of very thin gold layer deposited on a photosensitive polymer film. Under irradiation with light interference pattern, the azobenzene containing photosensitive polymer film undergoes deformation at which topography follows a distribution of intensity, resulting in the formation of a surface relief grating. This process is accompanied by a change in the shape of the polymer surface from flat to sinusoidal together with a corresponding increase in surface area. The gold layer placed above deforms along with the polymer and ruptures at a strain of 4%. The rupturing is spatially well defined, occurring at the topographic maxima and minima resulting in periodic cracks across the whole irradiated area. We have shown that this periodic micro-rupturing of a thin metal film has no significant impact on the electrical conductivity of the films. We suggest a model to explain this phenomenon and support this by additional experiments where the conductivity is measured in a process when a single nanoscopic scratch is formed with an AFM tip. Our results indicate that in flexible electronic materials consisting of a polymer support and an integrated metal circuit, nano-and micro cracks do not alter significantly the behavior of the conductivity unless the metal is disrupted completely. (C) 2013 AIP Publishing LLC. Y1 - 2013 U6 - https://doi.org/10.1063/1.4850595 SN - 0003-6951 SN - 1077-3118 VL - 103 IS - 25 PB - AMER INST PHYSICS CY - MELVILLE ER - TY - GEN A1 - Loebner, Sarah A1 - Jelken, Joachim A1 - Yadavalli, Nataraja Sekhar A1 - Sava, Elena A1 - Hurduc, Nicolae A1 - Santer, Svetlana T1 - Motion of adsorbed nano-particles on azobenzene containing polymer films N2 - We demonstrate in situ recorded motion of nano-objects adsorbed on a photosensitive polymer film. The motion is induced by a mass transport of the underlying photoresponsive polymer material occurring during irradiation with interference pattern. The polymer film contains azobenzene molecules that undergo reversible photoisomerization reaction from trans- to cis-conformation. Through a multi-scale chain of physico-chemical processes, this finally results in the macro-deformations of the film due to the changing elastic properties of polymer. The topographical deformation of the polymer surface is sensitive to a local distribution of the electrical field vector that allows for the generation of dynamic changes in the surface topography during irradiation with different light interference patterns. Polymer film deformation together with the motion of the adsorbed nano-particles are recorded using a homemade set-up combining an optical part for the generation of interference patterns and an atomic force microscope for acquiring the surface deformation. The particles undergo either translational or rotational motion. The direction of particle motion is towards the topography minima and opposite to the mass transport within the polymer film. The ability to relocate particles by photo-induced dynamic topography fluctuation offers a way for a non-contact simultaneous manipulation of a large number of adsorbed particles just in air at ambient conditions. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 352 KW - motion of adsorbed nano-particles KW - azobenzene containing polymer films KW - fluctuating surfaces Y1 - 2017 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-400423 ER - TY - JOUR A1 - Loebner, Sarah A1 - Jelken, Joachim A1 - Yadavalli, Nataraja Sekhar A1 - Sava, Elena A1 - Hurduc, Nicolae A1 - Santer, Svetlana T1 - Motion of Adsorbed Nano-Particles on Azobenzene Containing Polymer Films JF - Molecules N2 - We demonstrate in situ recorded motion of nano-objects adsorbed on a photosensitive polymer film. The motion is induced by a mass transport of the underlying photoresponsive polymer material occurring during irradiation with interference pattern. The polymer film contains azobenzene molecules that undergo reversible photoisomerization reaction from trans-to cis-conformation. Through a multi-scale chain of physico-chemical processes, this finally results in the macro-deformations of the film due to the changing elastic properties of polymer. The topographical deformation of the polymer surface is sensitive to a local distribution of the electrical field vector that allows for the generation of dynamic changes in the surface topography during irradiation with different light interference patterns. Polymer film deformation together with the motion of the adsorbed nano-particles are recorded using a homemade set-up combining an optical part for the generation of interference patterns and an atomic force microscope for acquiring the surface deformation. The particles undergo either translational or rotational motion. The direction of particle motion is towards the topography minima and opposite to the mass transport within the polymer film. The ability to relocate particles by photo-induced dynamic topography fluctuation offers a way for a non-contact simultaneous manipulation of a large number of adsorbed particles just in air at ambient conditions. KW - motion of adsorbed nano-particles KW - azobenzene containing polymer films KW - fluctuating surfaces Y1 - 2016 U6 - https://doi.org/10.3390/molecules21121663 SN - 1420-3049 VL - 21 SP - 397 EP - 411 PB - MDPI CY - Basel ER - TY - JOUR A1 - Loebner, Sarah A1 - Lomadze, Nino A1 - Kopyshev, Alexey A1 - Koch, Markus A1 - Guskova, Olga A1 - Saphiannikova, Marina A1 - Santer, Svetlana T1 - Light-Induced Deformation of Azobenzene-Containing Colloidal Spheres BT - Calculation and Measurement of Opto-Mechanical Stresses JF - The journal of physical chemistry : B, Condensed matter, materials, surfaces, interfaces & biophysical chemistry N2 - We report on light-induced deformation of colloidal spheres consisting of azobenzene-containing polymers. The colloids of the size between 60 nm and 2 mu m in diameter were drop casted on a glass surface and irradiated with linearly polarized light. It was found that colloidal particles can be deformed up to ca. 6 times of their initial diameter. The maximum degree of deformation depends on the irradiation wavelength and intensity, as well as on colloidal particles size. On the basis of recently proposed theory by Toshchevikov et al. [J. Phys. Chem. Lett. 2017, 8, 1094], we calculated the optomechanical stresses (ca. 100 MPa) needed for such giant deformations and compared them with the experimental results. Y1 - 2018 U6 - https://doi.org/10.1021/acs.jpcb.7b11644 SN - 1520-6106 VL - 122 IS - 6 SP - 2001 EP - 2009 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Loebner, Sarah A1 - Yadav, Bharti A1 - Lomadze, Nino A1 - Tverdokhleb, Nina A1 - Donner, Hendrik A1 - Saphiannikova, Marina A1 - Santer, Svetlana T1 - Local direction of optomechanical stress in azobenzene containing polymers during surface relief grating formation JF - Macromolecular materials and engineering N2 - In this work, it is revealed how the photoinduced deformation of azobenzene containing polymers relates to the local direction of optomechanical stresses generated during irradiation with interference patterns (IPs). It can be substantiated by the modeling approach proposed by Saphiannikova et al., which describes the directional photodeformations in glassy side-chain azobenzene polymers, and proves that these deformations arise from the reorientation of rigid backbone segments along the light polarization direction. In experiments and modeling, surface relief gratings in pre-elongated photosensitive colloids of few micrometers length are inscribed using different IPs such as SS, PP, +/- 45, SP, RL, and LR. The deformation of colloidal particles is studied in situ, whereby the local variation of polymer topography is assigned to the local distribution of the electrical field vector for all IPs. Experimentally observed shapes are reproduced exactly with modeling azopolymer samples as visco-plastic bodies in the finite element software ANSYS. Orientation approach correctly predicts local variations of the main axis of light-induced stress in each interference pattern for both initially isotropic and highly oriented materials. With this work, it is suggested that the orientation approach implements a self-sufficient and convincing mechanism to describe photoinduced deformation in azopolymer films that in principle does not require auxiliary assumptions. KW - azobenzene containing polymers KW - colloidal particles KW - direction of optomechanical stress KW - orientation approaches Y1 - 2022 U6 - https://doi.org/10.1002/mame.202100990 SN - 1438-7492 SN - 1439-2054 VL - 307 IS - 8 PB - Wiley-VCH CY - Weinheim ER - TY - JOUR A1 - Lomadze, Nino A1 - Kopyshev, Alexey A1 - Bargheer, Matias A1 - Wollgarten, Markus A1 - Santer, Svetlana T1 - Mass production of polymer nano-wires filled with metal nano-particles JF - Scientific reports N2 - Despite the ongoing progress in nanotechnology and its applications, the development of strategies for connecting nano-scale systems to micro-or macroscale elements is hampered by the lack of structural components that have both, nano-and macroscale dimensions. The production of nano-scale wires with macroscale length is one of the most interesting challenges here. There are a lot of strategies to fabricate long nanoscopic stripes made of metals, polymers or ceramics but none is suitable for mass production of ordered and dense arrangements of wires at large numbers. In this paper, we report on a technique for producing arrays of ordered, flexible and free-standing polymer nano-wires filled with different types of nano-particles. The process utilizes the strong response of photosensitive polymer brushes to irradiation with UV-interference patterns, resulting in a substantial mass redistribution of the polymer material along with local rupturing of polymer chains. The chains can wind up in wires of nano-scale thickness and a length of up to several centimeters. When dispersing nano-particles within the film, the final arrangement is similar to a core-shell geometry with mainly nano-particles found in the core region and the polymer forming a dielectric jacket. Y1 - 2017 U6 - https://doi.org/10.1038/s41598-017-08153-0 SN - 2045-2322 VL - 7 SP - 3759 EP - 3764 PB - Nature Publ. Group CY - London ER - TY - JOUR A1 - Lomadze, Nino A1 - Kopyshev, Alexey A1 - Bargheer, Matias A1 - Wollgarten, Markus A1 - Santer, Svetlana T1 - Mass production of polymer nanowires filled with metal nanoparticles JF - Scientific reports N2 - Despite the ongoing progress in nanotechnology and its applications, the development of strategies for connecting nano-scale systems to micro- or macroscale elements is hampered by the lack of structural components that have both, nano- and macroscale dimensions. The production of nano-scale wires with macroscale length is one of the most interesting challenges here. There are a lot of strategies to fabricate long nanoscopic stripes made of metals, polymers or ceramics but none is suitable for mass production of ordered and dense arrangements of wires at large numbers. In this paper, we report on a technique for producing arrays of ordered, flexible and free-standing polymer nano-wires filled with different types of nano-particles. The process utilizes the strong response of photosensitive polymer brushes to irradiation with UV-interference patterns, resulting in a substantial mass redistribution of the polymer material along with local rupturing of polymer chains. The chains can wind up in wires of nano-scale thickness and a length of up to several centimeters. When dispersing nano-particles within the film, the final arrangement is similar to a core-shell geometry with mainly nano-particles found in the core region and the polymer forming a dielectric jacket. Y1 - 2017 U6 - https://doi.org/10.1038/s41598-017-08153-0 SN - 2045-2322 VL - 7 PB - Springer Nature CY - London ER - TY - GEN A1 - Lomadze, Nino A1 - Kopyshev, Alexey A1 - Bargheer, Matias A1 - Wollgarten, Markus A1 - Santer, Svetlana T1 - Mass production of polymer nanowires filled with metal nanoparticles N2 - Despite the ongoing progress in nanotechnology and its applications, the development of strategies for connecting nano-scale systems to micro- or macroscale elements is hampered by the lack of structural components that have both, nano- and macroscale dimensions. The production of nano-scale wires with macroscale length is one of the most interesting challenges here. There are a lot of strategies to fabricate long nanoscopic stripes made of metals, polymers or ceramics but none is suitable for mass production of ordered and dense arrangements of wires at large numbers. In this paper, we report on a technique for producing arrays of ordered, flexible and free-standing polymer nano-wires filled with different types of nano-particles. The process utilizes the strong response of photosensitive polymer brushes to irradiation with UV-interference patterns, resulting in a substantial mass redistribution of the polymer material along with local rupturing of polymer chains. The chains can wind up in wires of nano-scale thickness and a length of up to several centimeters. When dispersing nano-particles within the film, the final arrangement is similar to a core-shell geometry with mainly nano-particles found in the core region and the polymer forming a dielectric jacket. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 387 Y1 - 2017 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-402712 ER - TY - JOUR A1 - Lomadze, Nino A1 - Kopyshev, Alexey A1 - Rühe, Jürgen A1 - Santer, Svetlana T1 - Light-Induced chain scission in photosensitive polymer brushes JF - Macromolecules : a publication of the American Chemical Society N2 - We report on a process inducing photomechanical fracture of chemical bonds in photosensitive PMAA polymer brushes. The photosensitive PMAA polymer brushes were prepared by covalent attachment of azobenzene groups to poly(methylacrylic acid) (PMAA) chains generated by surface-initiated polymerization. While homogeneous irradiation leaves the polymer topography unchanged, the azo-PMAA brushes show a strong response upon irradiation with UV interference patterns. The photoisomerization process in the surface-attached polymer films results in the irreversible formation of surface relief gratings (SRG), which are strongly enhanced upon washing with a good solvent for the polymer. The photomechanical forces during mass transport induced by the irradiation lead to the scission of covalent bounds and accordingly to a degrafting of the polymer chains in areas where the polymer is receding from. It is observed that the number of ruptured chains depends strongly on the amount of azo side chains in the polymer. Y1 - 2011 U6 - https://doi.org/10.1021/ma201016q SN - 0024-9297 VL - 44 IS - 18 SP - 7372 EP - 7377 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Lysyakova, Liudmila A1 - Lomadze, Nino A1 - Neher, Dieter A1 - Maximova, Ksenia A1 - Kabashin, Andrei V. A1 - Santer, Svetlana T1 - Light-Tunable Plasmonic Nanoarchitectures Using Gold Nanoparticle-Azobenzene-Containing Cationic Surfactant Complexes JF - The journal of physical chemistry : C, Nanomaterials and interfaces N2 - When arranged in a proper nanoaggregate architecture, gold nanoparticles can offer controllable plasmon-related absorption/scattering, yielding distinct color effects that depend critically on the relative orientation and distance between nanoparticle constituents. Herein, we report on the implementation of novel plasmonic nanoarchitectures based on complexes between gold nanoparticles and an azobenzene-modified cationic surfactant that can exhibit a light-tunable plasmonic response. The formation of such complexes becomes possible through the use of strongly negatively charged bare gold nanoparticles (similar to 10-nm diameter) prepared by the method of laser ablation in deionized water. Driven by electrostatic interactions, the cationic surfactant molecules attach and form a shell around the negatively charged nanoparticles, resulting in neutralization of the particle charge or even overcompensation beyond which the nanoparticles become positively charged. At low and high surfactant concentrations, Au nanoparticles are negatively and positively charged, respectively, and are represented by single species due to electric repulsion effects having absorption peaks around 523-527 nm, whereas at intermediate concentrations, the Au nanoparticles become neutral, forming nanoscale 100-nm clusterlike aggregates and exhibiting an additional absorption peak at gimel > 600 nm and a visible change in the color of the solution from red to blue. Because of the presence of the photosensitive azobenzene unit in the surfactant tail that undergoes trans-to-cis isomerization under irradiation with UV light, we then demonstrate a light-controlled nanoclustering of nanoparticles, yielding a switch in the plasmonic absorption band and a related change in the solution color. The formed hybrid architectures with a light-controlled plasmonic response could be important for a variety of tasks, including biomedical, surface-enhanced Raman spectroscopy (SERS), data transmission, and storage applications. Y1 - 2015 U6 - https://doi.org/10.1021/jp511232g SN - 1932-7447 VL - 119 IS - 7 SP - 3762 EP - 3770 PB - American Chemical Society CY - Washington ER -