极化条件对偶氮化合物薄膜中分子取向的影响

Effects of polarization conditions on molecular orientation in azo-dye compound film

为探索不同的极化条件对分子取向的影响,用旋涂法制备了偶氮主客体掺杂薄膜,并用电晕极化的方法分别在不同温度和厚度条件下使分子取向,通过测量极化前后紫外-可见吸收谱,研究了平均取向因子的变化,并和二次谐波产生结果进行了比较。实验结果表明:对于厚度相同的偶氮薄膜,随着温度的升高,平均取向因子增大,但二次谐波信号强度先增大后减小;温度越接近聚合物玻璃转变温度,分子越容易取向,但温度过高,聚甲基丙烯酸甲酯变为粘滞态,部分偶氮分子容易在高温下蒸发掉,导致二次谐波信号强度降低,而平均取向因子增大;随着薄膜厚度的增大,针-板电极电场造成薄膜内部电场分布的不均匀性增加,极化效率降低,平均取向因子不断减小,二次谐波信号强度先增大后减小。

In order to investigate the influence of polarization conditions on azo-dye molecular orientation in films,azo-dye polymer films of guest-host system were prepared by spin-coating method.The average alignment factor of azo-dye molecules in films were investigated by UV-Vis spectra measured before and after corona poling,as well as second harmonic generation at different corona poling conditions.The experimental results show that the average alignment factor of azo-dye films becomes bigger,and second harmonic intensity first increases and then decreases with the increasing of poling temperature.The closer the poling temperature is to the polymer＇s glass transition temperature,the more likely the molecules are orientated.However,PMMA will fall into a state of viscosity at too high temperature.A part of azo-dye molecules will evaporate easily at high temperature,making the second harmonic intensity decline and the average alignment factor increase.As the film thickness increases,the inhomogeneity of electric field distribution in films increases,which is caused by point-plane corona discharges,the polarization efficiency reduces,and therefore the average alignment factor decreases and the second harmonic intensity first increases and then decreases.