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 A. 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 - GEN A1 - Feldmann, David A1 - Maduar, Salim R. A1 - Santer, Mark A1 - Lomadze, Nino A1 - Vinogradova, Olga I. A1 - Santer, Svetlana A. 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 - Feldmann, David A1 - Maduar, Salim R. A1 - Santer, Mark A1 - Lomadze, Nino A1 - Vinogradova, Olga I. A1 - Santer, Svetlana A. 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 - JOUR A1 - Feldmann, David A1 - Maduar, Salim R. A1 - Santer, Mark A1 - Lomadze, Nino A1 - Vinogradova, Olga I. A1 - Santer, Svetlana A. 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 - Kopyshev, Alexey A1 - Galvin, Casey J. A1 - Genzer, Jan A1 - Lomadze, Nino A1 - Santer, Svetlana A. 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 - Moradi, N. A1 - Zakrevskyy, Yuriy A1 - Javadi, A. A1 - Aksenenko, E. V. A1 - Fainerman, V. B. A1 - Lomadze, Nino A1 - Santer, Svetlana A. A1 - Miller, R. T1 - Surface tension and dilation rheology of DNA solutions in mixtures with azobenzene-containing cationic surfactant JF - Colloids and surfaces : an international journal devoted to the principles and applications of colloid and interface science ; A, Physicochemical and engineering aspects N2 - The surface tension and dilational surface visco-elasticity of the individual solutions of the biopolymer DNA and the azobenzene-containing cationic surfactant AzoTAB, as well as their mixtures were measured using the drop profile analysis tensiometry. The negatively charged DNA molecules form complexes with the cationic surfactant AzoTAB. Mixed DNA + AzoTAB solutions exhibit high surface activity and surface layer elasticity. Extremes in the dependence of these characteristics on the AzoTAB concentration exist within the concentration range of 3 x 10(-6)-5 x 10(-5) M. The surface tension of the mixture shows a minimum with a subsequent maximum. In the same concentration range the elasticity shows first a maximum and then a subsequent minimum. A recently developed thermodynamic model was modified to account for the dependence of the adsorption equilibrium constant of the adsorbed complex on the cationic surfactant concentration. This modified theory shows good agreement with the experimental data both for the surface tension and the elasticity values over the entire range of studied AzoTAB concentrations. (C) 2016 Elsevier B.V. All rights reserved. KW - Mixed adsorption layers KW - Polymer/surfactant interaction KW - Water/air interface KW - Thermodynamics of adsorption KW - Dilational rheology KW - Drop profile analysis tensiometry Y1 - 2016 U6 - https://doi.org/10.1016/j.colsurfa.2016.04.021 SN - 0927-7757 SN - 1873-4359 VL - 505 SP - 186 EP - 192 PB - Elsevier CY - Amsterdam ER -