Optical materials based on cholesteric liquid crystals (LCs) doped with fluorescent CdSe/ZnS quantum dots (QDs) have been developed and demonstrated to have a wide photonic band gap. It has been shown that the fluorescence emission of QDs embedded in LCs is circularly polarized and that the dissymmetry factor of this polarization may be optically or electrically controlled via conformational changes in the helical structure of the LC matrix. The possibility of photochemical patterning or image recording using these materials has been demonstrated; the recorded information can be read through changes in the dissymmetry factor of circular polarization of QDs emission. The developed photo- and electro-active materials with a controlled degree of fluorescence circular polarization may be used as on-demand single photon sources in photonics, optoelectronics, and quantum cryptography, as well as for development of nanophotonic systems capable of low-threshold lasing.
The peculiarities of optical recording in the films of azo dye containing amorphous and liquid-crystalline polymers have been studied experimentally and theoretically. A simplified theoretical model of light induced processes in the azocontaining media has been elaborated. The model considers interaction of linearly-polarized light with a thin polymer layer. We derived analytical expressions for the light-induced refractive index and the absorption coefficient. Theoretical results are in good agreement with the experimental data. We have investigated features of holographic recording in amorphous and liquid-crystalline polymer samples. Recording of multiple holograms in polymer films with different structure was also demonstrated.
Orientational elastic deformations of polymer high temperature and reentrant nematics in a magnetic field were studied using the method of Freedericksz transitions. Experiments were performed on a series of fractions of a comb-like polymer. The temperature dependences of orientational elastic constants K1 and K3 in the nematic and reentrant nematic phases and birefringence (Delta) n and, correspondingly, the orientational order parameters S do not undergo a pronounced jump. The study of mechanical equilibrium characteristics did not reveal any differences in the behavior of high temperature and reentrant nematic phases of the polymer. For the lowest molecular weight fraction, an anomalous 'bell-shaped' temperature dependence of the bend constant K3 was found. This dependence can be explained by the formation of small domains with smectic ordering in the nematic phase. In the molecular weight range investigated, both optical anisotropy and equilibrium mechanical characteristics are independent of M.
The synthetic pathways of preparation of new optically active 1,1-binaphthyl (BN) derivatives containing various radicals including mesogenic ones were suggested and realized. No mesophase was found, but having atropisomeric chirality origin the novel substances proved to be effective chiral dopants inducing the highly twisted supramolecular structure both in low molecular mass and in polymer liquid crystals (LC). The helical twisting power (HTP) in two different standard nematic mixtures and in the copolymers based on the nematogenic methoxy-phenyl benzoate acrylic monomer was investigated. The systematic growth of the HTP in the low molecular mass nematics was found when the longer or mesogenic radicals were attached to the binaphthyl core. In the LC-copolymers the HTP of the BN-monomer and mesophase stability were analyzed depending on temperature and the molar fraction of the BN-fragments. The observed HTP value was found to be about thrice as much as those reported for the cholesterol and binaphthyl chiral monomers.
Dielectric relaxation and molecular mobility have ben investigated over the frequency range 60Hz-1MHz between 160 degrees C and 150 degrees C for smectic side-chain oligoacrylates with 4-cyanazobenzene mesogenic side groups and methylene spacers of different length. The studied oligomers were oriented by electric or mechanic fields. In the range of subglass temperatures two dielectric processes were observed - the (gamma) 1 and the (beta) . The (gamma) 1 process reflects the local motion of the spacer groups and the (beta) process is connected with the local motion of the mesogenic moieties. the molecular mobility of the (gamma) 1 process increases with the spacer lengthening but at the same time in the case of the (beta) process the mobility is not changed. In LC state near Tg transition, the temperature-frequency dependencies of dielectric losses show two cooperative processes, the (alpha) - an the (delta) , related to the reorientation of the transverse or longitudinal components of the dipole moment of the mesogenic group, correspondingly. The preliminary orientation in external electric or mechanic fields leads to the establishment of planar or homeotropic orientation of the side mesogenic groups. The order parameters of oriented films were calculated. It was shown the planar or homeotropic orientation of mesogenic groups did not influence on relaxation times of the observed dielectric processes.
Conference Committee Involvement (3)
Liquid Crystals and their Applications in Optics
17 April 2007 | Prague, Czech Republic
Electroactive Polymer Actuators and Devices (EAPAD)
15 March 2004 | San Diego, CA, United States
Electroactive Polymer Actuators and Devices (EAPAD)
3 March 2003 | San Diego, California, United States
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