光散射方法表征聚对苯二甲酰对苯二胺薄膜的结构特征

采用光散射方法研究了聚对苯二甲酰对苯二胺(PPTA)浓硫酸溶液于不同凝固条件下成膜时得到的球晶和草席晶等结构。PPTA的球晶由一些各向异性棒状微晶呈辐射型有序排列聚集而成的。红外二向色性的研究证明,PPTA草席晶中分子链沿“草席方向”高度取向。基于光栅衍射效应的角度依赖性认为,草席结构中条带的亮暗主要是由于它们取向方向上稍有差异引起的。以光栅效应计算了PPTA草席晶结构的长周期数据值及条带的取向状况,得到了较好的结果。根据在切应力作用下液晶的光散射图象认为,草席状结构是在切应力作用下于各向异性液业已形成,快速凝聚的方法可以把该种结构的特征保留在所获得的薄膜之中。

CHARACTERIZATION OF THE STRUCTURAL FEATURES OF THE POLY-p-PHENYLENE TEREPHTHALAMIDE (PPTA) FILMS BY LIGHT SCATTERING METHOD

The morphology of spherulite and mat-crystal structure in PPTA films coagulated from pure sulfuric acid solutions under different conditions has been studied by light scattering method.Unlike flexible chain polymers, the molecules of PPTA may aggregate not only to form the spherulites, but also some anisotropic rod-like domains at the same coagulation conditions.The results of infrared dichroism indicate that molecules within mat-crystal structure are highly oriented in the shearing direction (i. e. direction perpendicular to the band). According to the angular (angle between shearing direction and polarization direction of the analyzer) dependence of grating diffraction effect we suggest that the alternate change of brightness of parallelly arranged bands in the mat-crystal structure is primarily due to the slight difference in orientation direction of molecules within these bands. A method for calculating the number average long period (Pn) of the mat-crystal structure and the orientation of the bands from the diffraction patterns is proposed, and has been used successfully in characterization of PPTA films.Based on the light scattering studies of thin layers of the PPTA pure sulfuric acid solutions we have found that the mat-crystal structure is formed originally in the anisotropic PPTA solutions under shearing. After rapid coagulation of these layers the mat-crystal structure may be retained in the films obtained.