ИСТИНА

Creation of the self-assembled liquid crystalline (LC) hybrid composites is one of the hot topics in modern materials science. An intensive activity in this field is associated with a wide range of possible applications of such “smart” materials. One of the most promising properties predetermining this interest is the combination of unique optical properties of LC systems with specific optical or mechanical features of the different matrices. This report describes our results on the design and investigation of hybrid composites based on two types of polymer matrices and porous inorganic matrix: (i) porous polyethylene or polypropylene, (ii) porous cholesteric polymer networks and (iii) one-dimensional photonic crystals based on porous silicon. Filling these matrices with low-molar-mass photochromic LC mixtures or LC copolymers enables one to obtain composites with photovariable optical properties. In the first type of the composites, the highly anisotropic porous structure of polyolefin films provides uniaxial alignment of the nematic phase inside the pores. Introduction of photosensitive nematic mixtures containing azobenzene photochromic substances and fluorescent dopants allows one to realize dichroism, birefringence and polarized fluorescence photocontrol in the obtained LC composite films. Changing in these parameters takes place due to the reversible E-Z isomerization of the azobenzene chromophores leading to isothermal transition from nematic to isotropic state. The second type of the polymer scaffolds is prepared by the photopolymerization of the cholesteric mixtures containing mesogenic mono- and diacrylates followed by removing the low-molar-mass components that allows obtaining a highly porous cholesteric networks. Filling these scaffolds with photochromic LC mixtures capable of the isothermal photoinduced phase transition from nematic to isotropic state results in cholesteric films with phototunable position and width of selective light reflection peak. For the LC composites based on the porous cholesteric networks filled with azobenzene-containing LC copolymer the possibility of transmission and reflection holographic gratings recordings demonstrated. The third type of the composites presents photosensitive one-dimensional photonic crystals based on electrochemically etched porous silicon filled with low-molar-mass photochromic LC mixtures or copolymers containing azobenzene chromophores. Irradiation of these composites with UV light results in reversible E-Z isomerization of the azobenzene chromophores leading to isothermal transition from nematic to isotropic state. As a result spectral shift of photonic band gap position is observed. Polarized light induces photoorientation of the azobenzene chromophores in direction perpendicular to the light polarization and leads to spectral split of photonic stop band position. LC hybrid composites based on organic and inorganic porous matrices obtained and studied in this work can be considered as promising materials for the applications in photonics and optoelectronics.