片晶折叠表面成核机制与结晶温度的相关性研究

THE STUDY OF RELATIONSHIP BETWEEN NUCLEATION MECHANISM ON FOLDING SURFACE AND CRYSTALLIZAION TEMPERATURE

利用自晶种方法,在邻二氯苯稀溶液中培养聚丁二酸丁二醇酯(PBS)晶体,系统研究了结晶温度对其晶体形貌的影响.使用PBS单晶作为研究对象,有效避免小尺寸观察不具有统计意义的缺点.在结晶过程中,通过改变结晶温度和自晶种温度,可有效调控稀溶液中生长的PBS晶体尺寸大小和晶体中缺陷的数量,得到了单层无缺陷的单晶、双层晶体和多层晶体等一系列PBS片晶.基于对不同实验条件下得到片晶的形貌和表面粗糙度的统计结果,提出晶体中可容忍的缺陷数量与结晶温度和晶种温度密切相关这一结论,通过建立热力学模型,定性分析了晶体中缺陷数量和结晶温度的依赖关系,从片晶表面粗糙度统计结果出发,提出高分子片晶折叠表面成核机制,较好地解释了实验中观察到的不同PBS晶体的形貌.

The influence of temperature on the morphology of polybutylene succinate （PBS） lamellae, obtained by self-seeding crystallization in dilute dichloride benzene solution, was systematically studied. The morphologies of the PBS single crystals obtained by this method all have a similar size and shape. The atomic force microscopy measurements,such as the average surface roughness,were summarized over tens of the PBS crystals. It was found that the nucleation and the surface roughness of the folding surface of PBS lamellae were significantly influenced by the isothermal crystallization temperatures and the seeding temperatures. The higher the crystallization temperature,the larger the surface roughness can be found and it preferred to grow the single layer PBS crystals. It is suggested that the defects are mainly distributed on the folding surface. However, during crystallization at a relatively lower temperature,the smooth folding surface and multi-layers PBS crystals can be observed. We postulated that the defects may be trapped in the PBS crystal and to induce the screw dislocation growth to form the multi-layer morphology. Based on our experimental results, a simple model is proposed to qualitatively describe the relationship between the probability of defects in the lamellae and the supercooling degrees during the isothermal crystallization. Moreover, an inducing nucleation mechanism on folding surface of a crystal is also proposed,it can be used to explain our experimental observations.