@article{KoenigSanter2012, author = {K{\"o}nig, Tobias and Santer, Svetlana}, title = {Visualization of surface plasmon interference by imprinting intensity patterns on a photosensitive polymer}, series = {Nanotechnology}, volume = {23}, journal = {Nanotechnology}, number = {48}, publisher = {IOP Publ. Ltd.}, address = {Bristol}, issn = {0957-4484}, doi = {10.1088/0957-4484/23/48/485304}, pages = {7}, year = {2012}, abstract = {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.}, language = {en} } @article{TitovLysyakovaLomadzeetal.2015, author = {Titov, Evgenii and Lysyakova, Liudmila and Lomadze, Nino and Kabashin, Andrei V. and Saalfrank, Peter and Santer, Svetlana}, title = {Thermal Cis-to-Trans Isomerization of Azobenzene-Containing Molecules Enhanced by Gold Nanoparticles: An Experimental and Theoretical Study}, series = {The journal of physical chemistry : C, Nanomaterials and interfaces}, volume = {119}, journal = {The journal of physical chemistry : C, Nanomaterials and interfaces}, number = {30}, publisher = {American Chemical Society}, address = {Washington}, issn = {1932-7447}, doi = {10.1021/acs.jpcc.5b02473}, pages = {17369 -- 17377}, year = {2015}, abstract = {We report on the experimental and theoretical investigation of a considerable increase in the rate for thermal cis -> trans isomerization of azobenzene-containing molecules in the presence of gold nanopartides. Experimentally, by means of UV vis spectroscopy, we studied a series of azobenzene-containing surfactants and 4-nitroazobenzene. We found that in the presence of gold,nanoparticles the thermal lifetime of the cis isomer of the azobenzenecontaining molecules was decreased by up to 3 orders of magnitude in comparison to the lifetime in solution without nanoparticles. The electron transfer between azobenzene-containing molecules and a surface of gold nanopartides is a possible reason to promote the thermal cis trans switching. To investigate the effect of electron attachment to, and withdrawal from, the azobenzene-containing molecules on the isomerization rate, we performed density functional theory calculations of activation energy barriers of the reaction together with Eyring's transition state theory calculations of the rates for azobenzene derivatives with donor and acceptor groups in para position of one of the phenyl rings, as well as for one of the azobenzene-containing surfactants. We found that activation barriers are greatly lowered for azobenzene-containing molecules, both upon electron attachment and withdrawal, which leads, in turn, to a dramatic increase in the thermal isomerization rate.}, language = {en} } @article{RumyantsevSanterKramarenko2014, author = {Rumyantsev, Artem M. and Santer, Svetlana and Kramarenko, Elena Yu.}, title = {Theory of collapse and overcharging of a polyelectrolyte microgel induced by an oppositely charged surfactant}, series = {Macromolecules : a publication of the American Chemical Society}, volume = {47}, journal = {Macromolecules : a publication of the American Chemical Society}, number = {15}, publisher = {American Chemical Society}, address = {Washington}, issn = {0024-9297}, doi = {10.1021/ma500637d}, pages = {5388 -- 5399}, year = {2014}, abstract = {We report on the theoretical study of interaction of ionic surfactants with oppositely charged microgel particles in dilute solutions. Two approaches are proposed. Within the first approach, the micellization of the surfactants inside the microgel is taken into account while the second model focuses on the hydrophobic interactions of the surfactant tails with the hydrophobic parts of microgel subchains. It has been shown that microgels effectively absorb surfactant ions. At low surfactant concentration this absorption is realized due to an ion exchange between microgel counterions and surfactant ions. The ion exchange is significantly affected by the amount of the microgel counterions initially trapped within the microgel particles which depends on the size of the microgel, its ionization degree, cross-linking density as well as polymer concentration in the solution. Increase of the surfactant concentration causes contraction of the microgels, which can be realized as either a continuous shrinking or a jump-like collapse transition depending on the system parameters. In the collapsed state additional absorption of surfactants by microgels takes place due to an energy gain from micellization or hydrophobic interactions. This leads to microgel precipitation and successive microgel overcharging at an excess of the surfactant in the solution. The theoretical results are compared with the existing experimental data, in particular, on photosensitive surfactant/microgel complexes.}, language = {en} } @article{MalyarSanterStetsyura2013, author = {Malyar, Ivan V. and Santer, Svetlana and Stetsyura, Svetlana V.}, title = {The effect of illumination on the parameters of the polymer layer deposited from solution onto a semiconductor substrate}, series = {Technical physics letters : letters to the Russian journal of applied physics}, volume = {39}, journal = {Technical physics letters : letters to the Russian journal of applied physics}, number = {7}, publisher = {Pleiades Publ.}, address = {New York}, issn = {1063-7850}, doi = {10.1134/S1063785013070183}, pages = {656 -- 659}, year = {2013}, abstract = {The effect of illumination on the thickness and roughness of monolayers of polycationic molecules of polyethyleneimine deposited from solution onto a silicon substrate was discovered and investigated. The super-bandgap illumination of the substrate during polyethyleneimine adsorption causes a decrease in both the roughness and integral thickness of the organic layer on n- and p-Si substrates.}, language = {en} } @article{SchlemmerBetzBerchtoldetal.2009, author = {Schlemmer, Christian and Betz, Wolfgang and Berchtold, Bernd and R{\"u}he, J{\"u}rgen and Santer, Svetlana}, title = {The design of thin polymer membranes filled with magnetic particles on a microstructured silicon surface}, issn = {0957-4484}, doi = {10.1088/0957-4484/20/25/255301}, year = {2009}, abstract = {In this paper we present the fabrication and characterization of polymer nanomembranes filled with magnetic nanoparticles and attached covalently to a periodic array of free-standing silicon walls, forming an array of micro- channels with the membrane as a cover. The width of a micro-channel of about 1.4 mu m sets a characteristic lateral size and the thickness of the polymer membrane ranges between 100 and 300 nm. The membrane is made of cross-linked hydrophilic polymers possessing a Young's modulus of only a few MPa. The presence of the magnetic particles within the membrane makes the film responsive to external magnetic fields. The mechanical and magnetic properties of the membrane are characterized by bulge tests and with atomic force microscopy.}, language = {en} } @article{MoradiZakrevskyyJavadietal.2016, author = {Moradi, N. and Zakrevskyy, Yuriy and Javadi, A. and Aksenenko, E. V. and Fainerman, V. B. and Lomadze, Nino and Santer, Svetlana and Miller, R.}, title = {Surface tension and dilation rheology of DNA solutions in mixtures with azobenzene-containing cationic surfactant}, series = {Colloids and surfaces : an international journal devoted to the principles and applications of colloid and interface science ; A, Physicochemical and engineering aspects}, volume = {505}, journal = {Colloids and surfaces : an international journal devoted to the principles and applications of colloid and interface science ; A, Physicochemical and engineering aspects}, publisher = {Elsevier}, address = {Amsterdam}, issn = {0927-7757}, doi = {10.1016/j.colsurfa.2016.04.021}, pages = {186 -- 192}, year = {2016}, abstract = {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.}, language = {en} } @article{KoenigSekharSanter2012, author = {K{\"o}nig, Tobias and Sekhar, Y. Nataraja and Santer, Svetlana}, title = {Surface plasmon nanolithography impact of dynamically varying near-field boundary conditions at the air-polymer interface}, series = {Journal of materials chemistry}, volume = {22}, journal = {Journal of materials chemistry}, number = {13}, publisher = {Royal Society of Chemistry}, address = {Cambridge}, issn = {0959-9428}, doi = {10.1039/c2jm15864g}, pages = {5945 -- 5950}, year = {2012}, abstract = {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.}, language = {en} } @article{YadavalliSaphiannikovaLomadzeetal.2013, author = {Yadavalli, Nataraja Sekhar and Saphiannikova, Marina and Lomadze, Nino and Goldenberg, Leonid M. and Santer, Svetlana}, title = {Structuring of photosensitive material below diffraction limit using far field irradiation}, series = {Applied physics : A, Materials science \& processing}, volume = {113}, journal = {Applied physics : A, Materials science \& processing}, number = {2}, publisher = {Springer}, address = {New York}, issn = {0947-8396}, doi = {10.1007/s00339-013-7945-3}, pages = {263 -- 272}, year = {2013}, abstract = {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.}, language = {en} } @article{KoenigSanter2012, author = {K{\"o}nig, Tobias and Santer, Svetlana}, title = {Stretching and distortion of a photosensitive polymer film by surface plasmon generated near fields in the vicinity of a nanometer sized metal pin hole}, series = {Nanotechnology}, volume = {23}, journal = {Nanotechnology}, number = {15}, publisher = {IOP Publ. Ltd.}, address = {Bristol}, issn = {0957-4484}, doi = {10.1088/0957-4484/23/15/155301}, pages = {8}, year = {2012}, abstract = {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.}, 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} }