Abstract
Ferroelectric liquid crystalline polymers (FLCPs) with large spontaneous polarization, fast response and memory effect are suitable in electro-optical device application, such as display, light valve, and memory devices. Moreover, second-order nonlinear optical (NLO) polymers with large second-order nonlinearity and excellent temporal stability have potential for applications in the frequency doubling, electro-optical modulation, optical communication, and optical calculation etc. The goal of this endeavoPart I : Dielectric and electro-optical properties of side-chain FLCPsIn this study, dielectric relaxation behavior of a novel series of FLCPs with different mesogenic groups have been studied by a braodband dielectric spectroscopy. The influences of the chemical structural of mesogenic group and guest-host effect of azobenzene dyes on the dielectric relaxation behaviors and electro-optical properties are summarized as follows:(1) Spacer effect : Relaxation time and activation energies of the Goldstone mode, a, and b-relaxations decrease with increasing the length of the spacer due to the plasticizer effect of the spacer. Moreover, the relaxation intensity increases with increasing length of the spacer for the FLCPs. FLCP with a longer spacer length exhibits a higher mobility of the mesogenic group, and subsequently leads to easier reorientation toward the alternating electric field. However, the large molecular motion result(2) Mesogenic group effect : The increase of mesogenic core rigidity results in the increase of the relaxation time and activation energies, and decrease of the relaxation intensities for the Goldstone mode, a, and b-relaxations. Moreover, the b-relaxation was suppressed and could not be observed in the glassy state for the FLCPs containing the naphthyl biphenylcarboxylate as the mesogenic group. (3) Chiral moiety effect : Shorter relaxation time, smaller activation energies, and higher intensity of the a, and b-relaxations were obtained for the FLCPs containing chiral moiety with flexible heptyl alkyl chain. However, the relaxation intensity of Goldstone mode for the FLCPs containing this chiral moiety was smaller than that for the FLCPs containing chiral moiety with butyl alkyl chain. In addition, for the ones containing chiral moiety with two asymmetric centers, their Goldstone mode and b-rela(4) Mesogenic group content effect : Relaxation time and activation energies of the Goldstone mode, and b-relaxations decrease with decreasing content of the mesogenic group for the FLCPs. The relaxation intensity of the Goldstone mode is not decreased significantly as the content of the mesogenic group is lower than 35 mol. %. Moreover, the intensity of the b-relaxation was increases with decreasing content of mesogenic group. The mesogenic group was easier to be switched by the electric field for the (5) Guest-host effect : The doping of azobenzene dyes results in a smaller tilt angle and larger layer spacing of SC* phase for an FLCP. As a result, a larger intensity and higher frequency of Goldstone mode, and better electro-optical properties were obtained. Moreover, the doping effect on the dielectric behavior and electro-optical properties is more significant for the FLCP doped with strong dipole-moment guest molecules compared to that of the FLCP doped with weak dipole moment molecules. The stron Based on the above, it is concluded that dielectric relaxation study provides the important information of molecular motion for the rational design of FLCPs with excellent electro-optical properties. Part II：Dielectric and second-order optical nonlinearity of all sol-gel NLO materials. Second-order nonlinear optical polymer has been extensively studied for applications in photonic devices, such as frequency doubling and electro-optical (EO) modulation, because of their large optical nonlinearity, excellent processibility, low dielectric constants, and high laser damage thresholds. One of the NLO polymers is the sol-gel material. Sol-gel materials with second-order nonlinear optical properties are promising for applications in photonic devices for a number of reasons. These incl In this study, organically modified inorganic, organic, and organic-inorganic NLO materials via sol-gel reaction were developed. Thermal behavior, morphology, and second-order optical nonlinearities of the NLO materials are summarized as follows:(1) Organic modified inorganic NLO sol-gel materials: An alkoxysilane dye has been synthesized by the coupling of the alkoxysilane and azobenzene dye. The poled/cured alkoxysilane dye shows a large 2nd-order nonlinearity (d33 = 54.0 pm/V), but relatively poor temporal stability. The temporal stability was improved as the alkoxysilane dye was incorporated into the alkoxysilane based polymer matrix. The temporal stability of the poled/cured alkoxysilane dye increases with increasing content of alkoxysilan (2) Organic-inorganic NLO sol-gel materials (I) : A series of the organic-inorganic NLO sol-gel materials based on the melamines and alkoxysilane dye has been developed. By incorporating alkoxysilane dye into a organic sol-gel material, the resulting organic-inorganic hybrid may display the desired properties of both components. The poled/cured organic-inorganic NLO sol-gel materials shows a better temporal stability than the poled/cured alkoxysilane dye, especially the ones with equivalent weight ratio o(3) Organic NLO sol-gel materials: A series of the organic NLO sol-gel materials based on the melamines and an azobenzene dye has been developed. The poled/cured polymer films of the organic NLO sol-gel materials shows good optical quality and large 2nd-order nonlinearity (d33 = 35.4 pm/V) after poling process. The rigid NLO-active chromophores covalently bonded with the melamine-based matrices lead to the high rigidity and packing density of the organic network. Subsequently, a higher glass transition (4) Organic-inorganic NLO sol-gel materials (II) : A series of the organic-inorganic NLO sol-gel materials has been obtained by the incorporation of alkoxysilane into the melamine-based organic NLO sol-gel material with different weight ratios. A high degree mixing and the presence of the interaction between the organic and inorganic networks lead to the suppression of the molecular motion of chromophore. Subsequently, the temporal stability of the poled/cured organic NLO sol-gel materials was improved w In conclusion, these sol-gel NLO materials shows good optical quality and large second-order nonlinearity after poling at 220 ℃for 1 h. They exhibits excellent temporal stability at 100 ℃, which is outstanding among NLO sol-gel materials reported elsewhere. -1 -aDielectric and electro-optical properties of ferroelectric side-chain liquid crystalline and second-order nonlinear optical sol-gel polymers