侧链型偶氮聚合物液晶在不同温度条件下的光致取向

PHOTOINDUCED ORIENTATION OF AZOBENZENE LIQUID CRYSTAL POLYMER UNDER IRRADIATION AT DIFFERENT TEMPERATURE

在高于和低于玻璃化转变温度 (Tg)的温度范围内 ,研究了聚甲基丙烯酸 ( 6 [4 ( 4 氰基偶氮苯 )苯氧基 ]己酯 ) (Poly( 6 [4 ( 4 cyanophenylazo)phenoxy]hexylmethacrylate) (PM6ABCN) )聚合物膜的光致取向行为 .实验结果表明 ,在温度低于Tg 时 ,实验温度对取向速率没有影响 ;高于Tg 温度时 ,取向的速率随温度升高而变大 ,取向过程的表观活化能为 3 2 76kJ mol.通过对Tg 温度以下的光致取向进行分析 ,对光致取向过程提出了一个新的微相模型 ,微相内的温度能够达到Tg 以上 ,而实验中控制的样品宏观温度不变 ;高于Tg 温度时的光致取向过程受到宏观温度的控制 ,其表观活化能远远小于热致的各向同性相I(Isotropicphase,I)到向列相N(Nematicphase,N)相转变表观活化能 ( 3 40 2kJ mol) 。

A simple casting film of Poly (6-[4-(4-cyanophenylazo) phenoxy] hexyl metbacrylate) (PM6ABCN) was made on an untreated surface of a glass substrate and adopted as a typical sample to study photoinduced orientation of azobenzene liquid crystalline side chain homopolymers. Photoinduced orientation process of the sample was examined. A novel domain model was proposed to give a qualitative analysis of the photoinduced orientation below T-g. It was found that the experimental temperature had no effect on the rate of orientation, and within the domain the temperature higher than T-g was resulted from radiationless decay of absorbed light energy, and the orientation behavior of microscopic domains was identical with that of the macroscopic sample above T-g. An apparent activation energy of the orientation above T-g was found to be 32.76 kJ/mol. It means that this orientation process has a lower temperature dependence than that of the thermal I-N phase transition (340.2 kJ/mol).