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 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 - TY - JOUR A1 - Richter, Marcel A1 - Zakrevskyy, Yuriy A1 - Eisele, Michael A1 - Lomadze, Nino A1 - Santer, Svetlana A1 - von Klitzing, Regine T1 - Effect of pH, co-monomer content, and surfactant structure on the swelling behavior of microgel-azobenzene-containing surfactant complex JF - Polymer : the international journal for the science and technology of polymers N2 - The contraction/swelling transition of anionic PNIPAM-co-AAA particles can be manipulated by light using interactions with cationic azobenzene-containing surfactant. In this study the influence of pH-buffers and their concentrations, the charge density (AAA content) in microgel particles as well as the spacer length of the surfactant on the complex formation between the microgel and surfactant is investigated. It is shown that the presence of pH buffer can lead to complete blocking of the interactions in such complexes and the resulting microgel contraction/swelling response. There is a clear competition between the buffer ions and the surfactant molecules interacting with microgel particles. When working in pure water solutions with fixed concentration (charge density) of microgel, the contraction/swelling of the particles is controlled only by relative concentration (charge ratio) of the surfactant and AAA groups of the microgel. Furthermore, the particle contraction is more efficient for shorter spacer length of the surfactant. The onset point of the contraction process is not affected by the surfactant hydrophobicity. This work provides new insight into the interaction between microgel particles and photo-sensitive surfactants, which offers high potential in new sensor systems. (C) 2014 Elsevier Ltd. All rights reserved. KW - Hydrogel KW - Photosensitive surfactant KW - PNIPAM Y1 - 2014 U6 - https://doi.org/10.1016/j.polymer.2014.10.027 SN - 0032-3861 SN - 1873-2291 VL - 55 IS - 25 SP - 6513 EP - 6518 PB - Elsevier CY - Oxford ER - TY - CHAP A1 - Santer, Svetlana A1 - Zakrevskyy, Yuriy T1 - Reversible light-controlled compaction of soft colloids by azobenzene containing surfactant T2 - Abstracts of papers : joint conference / The Chemical Institute of Cananda, CIC, American Chemical Society, ACS Y1 - 2013 SN - 0065-7727 VL - 245 PB - American Chemical Society CY - Washington ER - TY - THES A1 - Zakrevskyy, Yuriy T1 - Liquid crystallinity and alignment of ionic self-assembly complexes T1 - Flüssigkristallinität und Alignment ionischer Self-Assembly Komplexe N2 - In this work the first observation of new type of liquid crystals is presented. This is ionic self-assembly (ISA) liquid crystals formed by introduction of oppositely charged ions between different low molecular tectonic units. As practically all conventional liquid crystals consist of rigid core and alkyl chains the attention is focused to the simplest case where oppositely charged ions are placed between a rigid core and alkyl tails. The aim of this work is to investigate and understand liquid crystalline and alignment properties of these materials. It was found that ionic interactions within complexes play the main role. Presence of these interactions restricts transition to isotropic phase. In addition, these interactions hold the system (like network) allowing crystallization into a single domain from aligned LC state. Alignment of these simple ISA complexes was spontaneous on a glass substrate. In order to show potentials for application perylenediimide and azobenzene containing ISA complexes have been investigated for correlations between phase behavior and their alignment properties. The best results of macroscopic alignment of perylenediimide-based ISA complexes have been obtained by zone-casting method. In the aligned films the columns of the complex align perpendicular to the phase-transition front. The obtained anisotropy (DR = 18) is thermally stable. The investigated photosensitive (azobenzene-based) ISA complexes show formation of columnar LC phases. It was demonstrated that photo alignment of such complexes was very effective (DR = 50 has been obtained). It was shown that photo-reorientation in the photosensitive ISA complexes is cooperative process. The size of domains has direct influence on efficiency of the photo-reorientation process. In the case of small domains the photo-alignment is the most effective. Under irradiation with linearly polarized light domains reorient in the plane of the film leading to macroscopic alignment of columns parallel to the light polarization and joining of small domains into big ones. Finally, the additional distinguishable properties of the ISA liquid crystalline complexes should be noted: (I) the complexes do not solve in water but readily solve in organic solvents; (II) the complexes have good film-forming properties when cast or spin-coated from organic solvent; (III) alignment of the complexes depends on their structure and secondary interactions between tectonic units. N2 - In dieser Arbeit wird erstmalig eine neue Klasse von Flüssigkristallen auf Basis ionischer Self-Assembly (ISA) Komplexe beschrieben. Während herkömmliche thermotrope Flüssigkristalle aus steifen, formanisotropen Molekülfragmenten und kovalent gebundenen Flügelgruppen (meist Alkylketten) bestehen, entstehen diese neuartigen supramolekularen Verbindungen durch die Komplexierung gegensätzlich geladener ionischer tektonischer Einheiten und Tenside. Ziel der Arbeit war es, die flüssigkristallinen und insbesondere die Orientierungseigenschaften dieser neuen Materialien am Beispiel repräsentativer Modellverbindungen zu untersuchen. Es wurde nachgewiesen, dass die ionischen Wechselwirkungen die thermischen Eigenschaften der Verbindungen entscheidend beeinflussen. So behindern sie den Übergang in die isotrope Phase. Das System wird quasi durch ein Netzwerk ionischer Wechselwirkungen stabilisiert. Makroskopisch orientierte LC Zustände sind offensichtlich Ausgangspunkt für hochgeordnete flüssigkristalline Filme oder gar für die Kristallisation von Monodomänen. In speziellen Fällen erfolgt eine spontane Ausbildung von ISA Monodomänen bereits auf Glassubstraten. Mit Hinblick auf potentielle Anwendungen wurden Perylendiimid und Azobenzen enthaltene ISA Komplexe insbesondere hinsichtlich von Zusammenhängen zwischen Phasenverhalten und Orientierungseigenschaften untersucht. Die zone-casting Methode erwies sich als besonders geeignet für die makroskopische Orientierung perylendiimidbasierter ISA Komplexe. In orientierten Filmen richten sich die Kolumnen des Komplexes senkrecht zur Phasenübergangsfront aus. Das dabei erreichte dichroitische Verhältnis (DR=18) ist thermisch stabil. Die untersuchten Azobenzen basierten ISA Komplexe weisen kolumnare LC Phasen auf. Durch Photoalignment mittels linear polarisierten Lichts werden Komplexe sehr effektiv senkrecht bzw. die Columnen der Komplexe parallel zur Polarisation des Lichtes orientiert, wobei sehr hohe DR bis zu 50 erreicht wurden. Weiterhin wurde gezeigt, dass die Photo-Reorientierung photosensitiver ISA Komplexe kooperativ erfolgt. Die Größe der Domänen hat dabei einen entscheidenden Einfluß auf die Effektivität des Photo-Reorientierungsprozesses. So ist der Prozess im Fall kleiner Domänen effektiver. Durch die Bestrahlung mit linear polarisiertem Licht werden die Domänen in der Filmebene reorientiert, was zu einer makroskopischen Ausrichtung der Kolumnen parallel zur Lichtpolarisation und zu einer Vereinigung kleiner Domänen führt. KW - Flüssigkristall KW - ionischer Self-Assembly KW - Komplex KW - Alignment KW - Liquid crystal KW - Ionic Self-Assembly KW - Complex KW - Alignment Y1 - 2006 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-10048 ER - TY - JOUR A1 - Zakrevskyy, Yuriy A1 - Cywinski, Piotr A1 - Cywinska, Magdalena A1 - Paasche, Jens A1 - Lomadze, Nino A1 - Reich, Oliver A1 - Löhmannsröben, Hans-Gerd A1 - Santer, Svetlana T1 - Interaction of photosensitive surfactant with DNA and poly acrylic acid JF - The journal of chemical physics : bridges a gap between journals of physics and journals of chemistr Y1 - 2014 U6 - https://doi.org/10.1063/1.4862679 SN - 0021-9606 SN - 1089-7690 VL - 140 IS - 4 PB - American Institute of Physics CY - Melville 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 - 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 - Roxlau, Julian A1 - Brezesinski, Gerald A1 - Lomadze, Nino A1 - Santer, Svetlana T1 - Photosensitive surfactants: Micellization and interaction with DNA JF - The journal of chemical physics : bridges a gap between journals of physics and journals of chemistr N2 - Recently, photosensitive surfactants have re-attracted considerable attention. It has been shown that their association with oppositely charged biologically important polyelectrolytes, such as DNA or microgels, can be efficiently manipulated simply by light exposure. In this article, we investigate the self-assembly of photosensitive surfactants as well as their interactions with DNA by calorimetric and spectroscopic methods. Critical micelle concentration (CMC), standard micellization enthalpy, entropy, and Gibbs energy were determined in different conditions (ionic strengths and temperatures) for a series of cationic surfactants with an azobenzene group in their tail. It is shown, that aggregation forces of photosensitive units play an important role in the micellization giving the major contribution to the micellization enthalpy. The onset of the aggregation can be traced from shift of the absorption peak position in the UV-visible spectrum. Titration UV-visible spectroscopy is used as an alternative, simple, and sensitive approach to estimate CMC. The titration UV-visible spectroscopy was also employed to investigate interactions (CAC: critical aggregation concentration, precipitation, and colloidal stabilization) in the DNA-surfactant complex. Y1 - 2014 U6 - https://doi.org/10.1063/1.4862678 SN - 0021-9606 SN - 1089-7690 VL - 140 IS - 4 PB - American Institute of Physics CY - Melville ER - TY - JOUR A1 - Zakrevskyy, Yuriy A1 - Titov, Evgenii A1 - Lomadze, Nino A1 - Santer, Svetlana T1 - Phase diagrams of DNA-photosensitive surfactant complexes: Effect of ionic strength and surfactant structure JF - The journal of chemical physics : bridges a gap between journals of physics and journals of chemistr N2 - Realization of all-optically controlled and efficient DNA compaction is the major motivation in the study of interactions between DNA and photosensitive surfactants. In this article, using recently published approach of phase diagram construction [Y. Zakrevskyy, P. Cywinski, M. Cywinska, J. Paasche, N. Lomadze, O. Reich, H.-G. Lohmannsroben, and S. Santer, J. Chem. Phys. 140, 044907 (2014)], a strategy for substantial reduction of compaction agent concentration and simultaneous maintaining the light-induced decompaction efficiency is proposed. The role of ionic strength (NaCl concentration), as a very important environmental parameter, and surfactant structure (spacer length) on the changes of positions of phase transitions is investigated. Increase of ionic strength leads to increase of the surfactant concentration needed to compact DNA molecule. However, elongation of the spacer results to substantial reduction of this concentration. DNA compaction by surfactants with longer tails starts to take place in diluted solutions at charge ratios Z < 1 and is driven by azobenzene-aggregation compaction mechanism, which is responsible for efficient decompaction. Comparison of phase diagrams for different DNA-photosensitive surfactant systems allowed explanation and proposal of a strategy to overcome previously reported limitations of the light-induced decompaction for complexes with increasing surfactant hydrophobicity. (C) 2014 AIP Publishing LLC. Y1 - 2014 U6 - https://doi.org/10.1063/1.4899281 SN - 0021-9606 SN - 1089-7690 VL - 141 IS - 16 PB - American Institute of Physics CY - Melville ER -