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 - Schimka, Selina A1 - Gordievskaya, Yulia D. A1 - Lomadze, Nino A1 - Lehmann, Maren A1 - von Klitzing, Regine A1 - Rumyantsev, Artem M. A1 - Kramarenko, Elena Yu. A1 - Santer, Svetlana T1 - Communication: Light driven remote control of microgels’ size in the presence of photosensitive surfactant: Complete phase diagram JF - The journal of chemical physics : bridges a gap between journals of physics and journals of chemistr N2 - Here we report on a light triggered remote control of microgel size in the presence of photosensitive surfactant. The hydrophobic tail of the cationic surfactant contains azobenzene group that undergoes a reversible photo-isomerization reaction from a trans-to a cis-state accompanied by a change in the hydrophobicity of the surfactant. We have investigated light assisted behaviour and the complex formation of the microgels with azobenzene containing surfactant over the broad concentrational range starting far below and exceeding several times of the critical micelle concentration (CMC). At small surfactant concentration in solution (far below CMC), the surfactant in the trans-state accommodates within the microgel causing its compaction, while the cis-isomer desorbs out of microgel resulting in its swelling. The process of the microgel size change can be described as swelling on UV irradiation (trans-cis isomerization) and shrinking on irradiation with blue light (cis-trans isomerization). However, at the surfactant concentrations larger than CMC, the opposite behaviour is observed: the microgel swells on blue irradiation and shrinks during exposure to UV light. We explain this behaviour theoretically taking into account isomer dependent micellization of surfactant within the microgels. Published by AIP Publishing. Y1 - 2017 U6 - https://doi.org/10.1063/1.4986143 SN - 0021-9606 SN - 1089-7690 VL - 147 PB - American Institute of Physics CY - Melville 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 - Yadavalli, Nataraja Sekhar A1 - Saphiannikova, Marina A1 - Lomadze, Nino A1 - Goldenberg, Leonid M. A1 - Santer, Svetlana T1 - Structuring of photosensitive material below diffraction limit using far field irradiation JF - Applied physics : A, Materials science & processing N2 - In this paper, we report on in-situ atomic force microscopy (AFM) studies of topographical changes in azobenzene-containing photosensitive polymer films that are irradiated with light interference patterns. We have developed an experimental setup consisting of an AFM combined with two-beam interferometry that permits us to switch between different polarization states of the two interfering beams while scanning the illuminated area of the polymer film, acquiring corresponding changes in topography in-situ. This way, we are able to analyze how the change in topography is related to the variation of the electrical field vector within the interference pattern. It is for the first time that with a rather simple experimental approach a rigorous assignment can be achieved. By performing in-situ measurements we found that for a certain polarization combination of two interfering beams [namely for the SP (a dagger center dot, a dagger") polarization pattern] the topography forms surface relief grating with only half the period of the interference patterns. Exploiting this phenomenon we are able to fabricate surface relief structures with characteristic features measuring only 140 nm, by using far field optics with a wavelength of 491 nm. We believe that this relatively simple method could be extremely valuable to, for instance, produce structural features below the diffraction limit at high-throughput, and this could significantly contribute to the search of new fabrication strategies in electronics and photonics industry. Y1 - 2013 U6 - https://doi.org/10.1007/s00339-013-7945-3 SN - 0947-8396 SN - 1432-0630 VL - 113 IS - 2 SP - 263 EP - 272 PB - Springer CY - New York 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 - Zakrevskyy, Yuriy A1 - Richter, Marcel A1 - Zakrevska, Svitlana A1 - Lomadze, Nino A1 - von Klitzing, Regine A1 - Santer, Svetlana T1 - Light-controlled reversible manipulation of microgel particle size using azobenzene-containing surfactant JF - Advanced functional materials N2 - The light-induced reversible switching of the swelling of microgel particles triggered by photo-isomerization and binding/unbinding of a photosensitive azobenzene-containing surfactant is reported. The interactions between the microgel (N-isopropylacrylamide, co-monomer: allyl acetic acid, crosslinker: N,N'-methylenebisacrylamide) and the surfactant are studied by UV-Vis spectroscopy, dynamic and electrophoretic light scattering measurements. Addition of the surfactant above a critical concentration leads to contraction/collapse of the microgel. UV light irradiation results in trans-cis isomerization of the azobenzene unit incorporated into the surfactant tail and causes an unbinding of the more hydrophilic cis isomer from the microgel and its reversible swelling. The reversible contraction can be realized by blue light irradiation that transfers the surfactant back to the more hydrophobic trans conformation, in which it binds to the microgel. The phase diagram of the surfactant-microgel interaction and transitions (aggregation, contraction, and precipitation) is constructed and allows prediction of changes in the system when the concentration of one or both components is varied. Remote and reversible switching between different states can be realized by either UV or visible light irradiation. Y1 - 2012 U6 - https://doi.org/10.1002/adfm.201200617 SN - 1616-301X VL - 22 IS - 23 SP - 5000 EP - 5009 PB - Wiley-VCH CY - Weinheim ER - TY - JOUR A1 - Zakrevskyy, Yuriy A1 - Kopyshev, Alexey A1 - Lomadze, Nino A1 - Morozova, Elena A1 - Lysyakova, Liudmila A1 - Kasyanenko, Nina A1 - Santer, Svetlana T1 - DNA compaction by azobenzene-containing surfactant JF - Physical review : E, Statistical, nonlinear and soft matter physics N2 - We report on the interaction of cationic azobenzene-containing surfactant with DNA investigated by absorption and fluorescence spectroscopy, dynamic light scattering, and atomic force microscopy. The properties of the surfactant can be controlled with light by reversible switching of the azobenzene unit, incorporated into the surfactant tail, between a hydrophobic trans (visible irradiation) and a hydrophilic cis (UV irradiation) configuration. The influence of the trans-cis isomerization of the azobenzene on the compaction process of DNA molecules and the role of both isomers in the formation and colloidal stability of DNA-surfactant complexes is discussed. It is shown that the trans isomer plays a major role in the DNA compaction process. The influence of the cis isomer on the DNA coil configuration is rather small. The construction of a phase diagram of the DNA concentration versus surfactant/DNA charge ratio allows distancing between three major phases: colloidally stable and unstable compacted globules, and extended coil conformation. There is a critical concentration of DNA above which the compacted globules can be hindered from aggregation and precipitation by adding an appropriate amount of the surfactant in the trans configuration. This is because of the compensation of hydrophobicity of the globules with an increasing amount of the surfactant. Below the critical DNA concentration, the compacted globules are colloidally stable and can be reversibly transferred with light to an extended coil state. Y1 - 2011 U6 - https://doi.org/10.1103/PhysRevE.84.021909 SN - 1539-3755 VL - 84 IS - 2 PB - American Physical Society CY - College Park ER - TY - JOUR A1 - Schuh, Christian A1 - Lomadze, Nino A1 - Rühe, Jürgen A1 - Kopyshev, Alexey A1 - Santer, Svetlana T1 - Photomechanical degrafting of Azo-functionalized Poly(methacrylic acid) (PMAA) brushes JF - The journal of physical chemistry : B, Condensed matter, materials, surfaces, interfaces & biophysical chemistry N2 - We report on the preparation and characterization of photosensitive polymer brushes. The brushes are synthesized through polymer analogous attachment of azobenzene groups to surface-attached poly(methacrylic acid) (PMAA) chains. The topography of the photosensitive brushes shows a strong reaction upon irradiation with UV light. While homogeneous illumination leaves the polymer topography unchanged, irradiation of the samples with interference patterns with periodically varying light intensity leads to the formation of surface relief gratings (SRG). The height of the stripes of the grating can be controlled by adjusting the irradiation time. The SRG pattern can be erased through solvent treatment when the periodicity of the stripe pattern is less than the length of the fully stretched polymer chains. In the opposite case, photomechanical scission of receding polymer chains is observed during SRG formation, and the inscribed patterns are permanent. Y1 - 2011 U6 - https://doi.org/10.1021/jp2041229 SN - 1520-6106 VL - 115 IS - 35 SP - 10431 EP - 10438 PB - American Chemical Society CY - Washington 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 - CHAP A1 - Schuh, Christian A1 - Prucker, Oswald A1 - Lomadze, Nino A1 - Kopyshev, Alexey A1 - Santer, Svetlana A1 - Ruehe, Juergen T1 - Nanogradient polymer brushes T2 - Abstracts of papers : joint conference / The Chemical Institute of Cananda, CIC, American Chemical Society, ACS Y1 - 2012 SN - 0065-7727 VL - 243 PB - American Chemical Society CY - Washington ER -