@article{AryaFeldmannKopyshevetal.2020, author = {Arya, Pooja and Feldmann, David and Kopyshev, Alexey and Lomadze, Nino and Santer, Svetlana}, title = {Light driven guided and self-organized motion of mesoporous colloidal particles}, series = {Soft matter}, volume = {16}, journal = {Soft matter}, number = {5}, publisher = {Royal Society of Chemistry}, address = {Cambridge}, issn = {1744-683X}, doi = {10.1039/c9sm02068c}, pages = {1148 -- 1155}, year = {2020}, abstract = {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.}, language = {en} } @article{AryaJelkenFeldmannetal.2020, author = {Arya, Pooja and Jelken, Joachim and Feldmann, David and Lomadze, Nino and Santer, Svetlana}, title = {Light driven diffusioosmotic repulsion and attraction of colloidal particles}, series = {The journal of chemical physics : bridges a gap between journals of physics and journals of chemistr}, volume = {152}, journal = {The journal of chemical physics : bridges a gap between journals of physics and journals of chemistr}, number = {19}, publisher = {American Institute of Physics}, address = {Melville, NY}, issn = {0021-9606}, doi = {10.1063/5.0007556}, pages = {10}, year = {2020}, abstract = {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.}, language = {en} } @article{AryaJelkenLomadzeetal.2020, author = {Arya, Pooja and Jelken, Joachim and Lomadze, Nino and Santer, Svetlana and Bekir, Marek}, title = {Kinetics of photo-isomerization of azobenzene containing surfactants}, series = {The journal of chemical physics : bridges a gap between journals of physics and journals of chemistry}, volume = {152}, journal = {The journal of chemical physics : bridges a gap between journals of physics and journals of chemistry}, number = {2}, publisher = {American Institute of Physics}, address = {Melville}, issn = {0021-9606}, doi = {10.1063/1.5135913}, pages = {10}, year = {2020}, abstract = {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.}, language = {en} } @article{JelkenHenkelSanter2020, author = {Jelken, Joachim and Henkel, Carsten and Santer, Svetlana}, title = {Polarization controlled fine structure of diffraction spots from an optically induced grating}, series = {Applied physics letters}, volume = {116}, journal = {Applied physics letters}, number = {5}, publisher = {American Institute of Physics}, address = {Melville}, issn = {0003-6951}, doi = {10.1063/1.5140067}, pages = {4}, year = {2020}, abstract = {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.}, language = {en} } @article{JelkenHenkelSanter2020, author = {Jelken, Joachim and Henkel, Carsten and Santer, Svetlana}, title = {Formation of half-period surface relief gratings in azobenzene containing polymer films}, series = {Applied physics : B, Lasers and optics}, volume = {126}, journal = {Applied physics : B, Lasers and optics}, number = {9}, publisher = {Springer}, address = {Heidelberg}, issn = {0946-2171}, doi = {10.1007/s00340-020-07500-w}, pages = {14}, year = {2020}, abstract = {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.}, language = {en} } @misc{SharmaBekirLomadzeetal.2020, author = {Sharma, Anjali and Bekir, Marek and Lomadze, Nino and Santer, Svetlana}, title = {Photo-Isomerization Kinetics of Azobenzene Containing Surfactant Conjugated with Polyelectrolyte}, series = {Postprints der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe}, journal = {Postprints der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe}, number = {1101}, issn = {1866-8372}, doi = {10.25932/publishup-48942}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-489427}, pages = {14}, year = {2020}, abstract = {Ionic complexation of azobenzene-containing surfactants with any type of oppositely charged soft objects allows for making them photo-responsive in terms of their size, shape and surface energy. Investigation of the photo-isomerization kinetic and isomer composition at a photo-stationary state of the photo-sensitive surfactant conjugated with charged objects is a necessary prerequisite for understanding the structural response of photo-sensitive complexes. Here, we report on photo-isomerization kinetics of a photo-sensitive surfactant in the presence of poly(acrylic acid, sodium salt). We show that the photo-isomerization of the azobenzene-containing cationic surfactant is slower in a polymer complex compared to being purely dissolved in aqueous solution. In a photo-stationary state, the ratio between the trans and cis isomers is shifted to a higher trans-isomer concentration for all irradiation wavelengths. This is explained by the formation of surfactant aggregates near the polyelectrolyte chains at concentrations much lower than the bulk critical micelle concentration and inhibition of the photo-isomerization kinetics due to steric hindrance within the densely packed aggregates.}, language = {en} } @article{SharmaBekirLomadzeetal.2020, author = {Sharma, Anjali and Bekir, Marek and Lomadze, Nino and Santer, Svetlana}, title = {Photo-Isomerization Kinetics of Azobenzene Containing Surfactant Conjugated with Polyelectrolyte}, series = {Molecules}, volume = {29}, journal = {Molecules}, number = {1}, publisher = {MDPI}, address = {Basel}, issn = {1420-3049}, doi = {10.3390/molecules26010019}, pages = {12}, year = {2020}, abstract = {Ionic complexation of azobenzene-containing surfactants with any type of oppositely charged soft objects allows for making them photo-responsive in terms of their size, shape and surface energy. Investigation of the photo-isomerization kinetic and isomer composition at a photo-stationary state of the photo-sensitive surfactant conjugated with charged objects is a necessary prerequisite for understanding the structural response of photo-sensitive complexes. Here, we report on photo-isomerization kinetics of a photo-sensitive surfactant in the presence of poly(acrylic acid, sodium salt). We show that the photo-isomerization of the azobenzene-containing cationic surfactant is slower in a polymer complex compared to being purely dissolved in aqueous solution. In a photo-stationary state, the ratio between the trans and cis isomers is shifted to a higher trans-isomer concentration for all irradiation wavelengths. This is explained by the formation of surfactant aggregates near the polyelectrolyte chains at concentrations much lower than the bulk critical micelle concentration and inhibition of the photo-isomerization kinetics due to steric hindrance within the densely packed aggregates.}, language = {en} } @article{SilantevaKomolkinMamontovaetal.2020, author = {Silanteva, Irina A. and Komolkin, Andrei and Mamontova, Veronika V. and Vorontsov-Velyaminov, Pavel N. and Santer, Svetlana and Kasyanenko, Nina A.}, title = {Some features of surfactant organization in DNA solutions at various NaCl concentrations}, series = {ACS omega / American Chemical Society}, volume = {5}, journal = {ACS omega / American Chemical Society}, number = {29}, publisher = {ACS Publications}, address = {Washington}, issn = {2470-1343}, doi = {10.1021/acsomega.0c01850}, pages = {18234 -- 18243}, year = {2020}, abstract = {The photosensitive azobenzene-containing surfactant C-4-Azo-OC(6)TMAB is a promising agent for reversible DNA packaging in a solution. The simulation of the trans-isomer surfactant organization into associates in a solution with and without salt as well as its binding to DNA at different NaCl concentrations was carried out by molecular dynamics. Experimental data obtained by spectral and hydrodynamic methods were used to verify the results of simulation. It was shown that head-to-tail aggregates with close to antiparallel orientation of surfactant molecules were formed at certain NaCl and surfactant concentrations (below critical micelle concentration). Such aggregates have two positively charged ends, and therefore, they can be attracted to negatively charged DNA phosphates far located along the chain, as well as those that belong to different molecules. This contributes to the formation of intermolecular DNA-DNA contacts, and this way, the experimentally observed precipitation of DNA can be explained.}, language = {en} } @article{SimonovaIvanovMeleshkoetal.2020, author = {Simonova, Maria and Ivanov, Ivan and Meleshko, Tamara and Kopyshev, Alexey and Santer, Svetlana and Yakimansky, Alexander and Filippov, Alexander}, title = {Self-assembly of molecular brushes with polyimide backbone and amphiphilic block copolymer side chains in selective solvents}, series = {Polymers}, volume = {12}, journal = {Polymers}, number = {12}, publisher = {MDPI}, address = {Basel}, issn = {2073-4360}, doi = {10.3390/polym12122922}, pages = {15}, year = {2020}, abstract = {Three-component molecular brushes with a polyimide backbone and amphiphilic block copolymer side chains with different contents of the "inner" hydrophilic (poly(methacrylic acid)) and "outer" hydrophobic (poly(methyl methacrylate)) blocks were synthesized and characterized by molecular hydrodynamics and optics methods in solutions of chloroform, dimethylformamide, tetrahydrofuran and ethanol. The peculiarity of the studied polymers is the amphiphilic structure of the grafted chains. The molar masses of the molecular brushes were determined by static and dynamic light scattering in chloroform in which polymers form molecularly disperse solutions. Spontaneous self-assembly of macromolecules was detected in dimethylformamide, tetrahydrofuran and ethanol. The aggregates size depended on the thermodynamic quality of the solvent as well as on the macromolecular architectural parameters. In dimethylformamide and tetrahydrofuran, the distribution of hydrodynamic radii of aggregates was bimodal, while in ethanol, it was unimodal. Moreover, in ethanol, an increase in the poly(methyl methacrylate) content caused a decrease in the hydrodynamic radius of aggregates. A significant difference in the nature of the blocks included in the brushes determines the selectivity of the used solvents, since their thermodynamic quality with respect to the blocks is different. The macromolecules of the studied graft copolymers tend to self-organization in selective solvents with formation of a core-shell structure with an insoluble solvophobic core surrounded by the solvophilic shell of side chains.}, language = {en} } @article{UmlandtFeldmannSchnecketal.2020, author = {Umlandt, Maren and Feldmann, David and Schneck, Emanuel and Santer, Svetlana and Bekir, Marek}, title = {Adsorption of photoresponsive surfactants at solid-liquid interfaces}, series = {Langmuir}, volume = {36}, journal = {Langmuir}, number = {46}, publisher = {American Chemical Society}, address = {Washington}, issn = {0743-7463}, doi = {10.1021/acs.langmuir.0c02545}, pages = {14009 -- 14018}, year = {2020}, abstract = {We report on the adsorption kinetics of azoben-zene-containing surfactants on solid surfaces of different hydrophobicity. The understanding of this processes is of great importance for many interfacial phenomena that can be actuated and triggered by light, since the surfactant molecules contain a photoresponsive azobenzene group in their hydrophobic tail. Three surfactant types are studied, differing in the spacer connecting the headgroup and the azobenzene unit by between 6 and 10 CH2 groups. Under irradiation with light of a suitable wavelength, the azobenzene undergoes reversible photoisomerization between two states, a nonpolar trans-state and a highly polar cis-state. Consequently, the surfactant molecule changes its hydrophobicity and thus affinity to a surface depending on the photoisomerization state of the azobenzene. The adsorption behavior on hydrophilic (glass) and hydrophobic (TeflonAF) surfaces is analyzed using quartz crystal microbalance with dissipation (QCM-D) and zeta-potential measurements. At equilibrium, the adsorbed surfactant amount is almost twice as large on glass compared to TeflonAF for both isomers. The adsorption rate for the trans-isomers on both surfaces is similar, but the desorption rate of the trans-isomers is faster at the glass-water interface than at the Teflon-water interface. This result demonstrates that the trans-isomers have higher affinity for the glass surface, so the trans-to-cis ratios on glass and TeflonAF are 80/1 and 2/1, respectively, with similar trends for all three surfactant types.}, language = {en} }