TY - JOUR A1 - Ryabchun, Alexander A1 - Raguzin, Ivan A1 - Stumpe, Joachim A1 - Shibaev, Valery A1 - Bobrovsky, Alexey T1 - Cholesteric Polymer Scaffolds Filled with Azobenzene-Containing Nematic Mixture with Phototunable Optical Properties JF - Scientific reports N2 - The past two decades witnessed tremendous progress in the field of creation of different types of responsive materials. Cholesteric polymer networks present a very promising class of smart materials due to the combination of the unique optical properties of cholesteric mesophase and high mechanical properties of polymer networks. In the present work we demonstrate the possibility of fast and reversible photocontrol of the optical properties of cholesteric polymer networks. Several cholesteric photopolymerizable mixtures are prepared, and porous cholesteric network films with different helix pitches are produced by polymerization of these mixtures. An effective and simple method of the introduction of photochromic azobenzene-containing nematic mixture capable of isothermal photoinducing the nematic isotropic phase transition into the porous polymer matrix is developed, It is found that cross-linking density and degree of polymer network filling with a photochromic nematic mixture strongly influence the photo-optical behavior of the obtained composite films. In particular, the densely cross-linked films are characterized by a decrease in selective light reflection bandwidth, whereas weakly cross-linked systems display two processes: the shift of selective light reflection peak and decrease of its width. It is noteworthy that the obtained cholesteric materials are shown to be very promising for the variety applications in optoelectronics and photonics. KW - liquid crystalline polymer KW - azobenzene KW - cholesteric phase KW - phototunable optical properties KW - selective light reflection KW - LC composites Y1 - 2016 U6 - https://doi.org/10.1021/acsami.6b09642 SN - 1944-8244 VL - 8 SP - 27227 EP - 27235 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Ryabchun, Alexander A1 - Sakhno, Oksana A1 - Stumpe, Joachim A1 - Bobrovsky, Alexey T1 - Full-Polymer Cholesteric Composites for Transmission and Reflection Holographic Gratings JF - Advanced optical materials N2 - A new type of self-organized materials based on cholesteric networks filled with photoactive side-chain copolymer is being developed. Supramolecular helical structure of cholesteric polymer network resulting in the selective reflection is used as a photonic scaffold. Photochromic azobenzene-containing nematic copolymer is embedded in cholesteric scaffold and utilized as a photoactive media for optical pattering. 1D and 2D transmission diffraction gratings are successfully recorded in composite films by holographic technique. For the first time the possibility to create selective reflection gratings in cholesteric material mimicking the natural optical properties of cholesteric mesophase is demonstrated. That enables the coexistence of two selective gratings, where one has an intrinsic cholesteric periodic helical structure and the other is a holographic grating generated in photochromic polymer. The full-polymer composites provide high light-induced optical anisotropy due to effective photo-orientation of side-chain fragments of the azobenzene-containing liquid crystalline polymer, and prevent the degradation of the helical superstructure maintaining all optical properties of cholesteric mesophase. The proposed class of optical materials could be easily applied to a broad range of polymeric materials with specific functionality. The versatility of the adjustment and material preprogramming combined with high optical performance makes these materials a highly promising candidate for modern optical and photonic applications. KW - azobenzene KW - cholesteric scaffolds KW - holography KW - LC polymer KW - polarization diffraction grating KW - reflection grating Y1 - 2017 U6 - https://doi.org/10.1002/adom.201700314 SN - 2195-1071 VL - 5 SP - 376 EP - 379 PB - Wiley-VCH CY - Weinheim ER -