Study On Preparation And Properties Of The Photorefractive Composites Based On Poly(N-Vinylcarbazole) Grafted By (P-Nitrobenzene) Azo

Photorefractive material has attracted considerable attention and greatly interesting due to its potential important applications in optical processing and holographic data storage, which becomes hot research at the present. However, researchs on the phase stability and descreasing applied electric field for the host-gouest photorefractive polymer composites are not enough in extension and intension. We have studied on preparation of Poly(N-vinylcarbazole)( PVK) grafted by (p-nitrobenzene) azo (PVK-azo)and chromophores in this paper, and properties of new photorefractive polymer composites such as phase stability,photoconductivity, photorefractive and trap state, in order to provide experimental data and theoretical foundation for practical applications of photorefractive polymers.1. Synthesis of the PVK has been investigated. The results showed that PVK was prepared successfully though new synthesis technology.2. A series of carbazole-based polymers (PVK-azo) containing different azo group were prepared via a post azo coupling reaction. The molecular structure of PVK-azo was characterized by IR, 1H-NMR, UV-vis, DSC and GPC. The results of IR and 1H-NMR demonstrated that azo group had been substituted to PVK. From the UV-vis spectrum, it could be seen that the content of azo group raise from 8.7% to 58.1% when reaction conditions( the different reaction time, temperature, amount of catalyst and the ratio of reactants) were changed. The results of GPC and DSC showed that the molecular weight and Tg of PVK-azo were higher than that of PVK.3. A series of nonlinear chromophore molecules 4 - n-alkoxy-4 - cyano-2 biphenyl (nOCB) were prepared. The chemical structures of these were characterized by IR and 1H-NMR.4. The photoconductivity properties of the PVK, PVK-azo and its composites were studied by photocurrent method and the density functional theory calculating method. The results showed that photoconductivity of PVK-azo obviously higher than that of the PVK, and which was increased with increasing content of azo group of PVK-azo.5. The phase stability of PVK-azo/nOCB/C60 and PVK/nOCB/C60 composites was investigated through the transmittance light method and scanning electron microscopy (SEM). The results showed that phase stability of the former (more than one year) greatly exceeded that of the latter (one day). Furthermore, the phase stability of PVK-azo/nOCB/C60 composites increased with increasing the content of zao group of PVK-azo.6. Two-beam coupling gain coefficient(Г) of composites composed of PVK-azo/nOCB/C60 was studied. The results showed that: 1) Photorefractive effect and two-beam coupling gain phenomenon of that composites have been discovered under the zero external electric field. 2)Гof the composites increased with increasing the content of azo group of PVK-azo 3) With increasing n of nOCB in PVK-azo/nOCB/C60, sequence ofГgone as follow:8 OCB> 6OCB> 5OCB 4). We also found that light energy transfer direction bewteen the two coherent beams is related to light incidence angle at zero applied electric field. For instance, two-beam coupling experimental conditions for PVK-azo/6OCB /C60 (59.8/40/0.2 wt%) as follow: When light incidence angle (40°) bewteen the two beams (I10,I20) and the ratio of intensity of two beams light (I20 /I10,1.785) keep invariant,the I10 energy transfer to the I20(Г≤0) as I10 angle(θ1) with the normal direction changes from 0°to 25°. While theθ1 changes from 26°to 40°, the I20 energy is transfered to the I10 (Г> 0).7. The diffraction efficiency of the steady-state grating for PVK-azo/nOCB/C60 was investigated. The results showed that the diffraction efficiency increased with increasing content of azo group of PVK-azo at the zero applied electric field. Forthuremore, the diffraction efficiency can be obviously varied with strength and direction of applied electric field.8. Polarization relaxation and trap state of PVK/ECZ/C60 and PVK-azo/ECZ/C60 was investigated by Thermally Stimulated Current (TSC). The results showed that: 1) Relaxation activation energy of PVK-azo was higher than that of PVK 2) The traps was origin mainly from the trap of nonlinear chromophore and the value of traps energy depth is about 0.45-0.6eV.