偏振光学显微成像技术在高分子结晶结构表征中的应用

Polarized Optical Imaging and Its Application in Characterization of Polymer Crystalline Structures

光学成像技术是最为直观的一种表征手段,借助光学显微镜,根据物质、材料和光的相互作用,能够直接观察肉眼难以获得的微观结构信息.借助偏振光,又能看到在普通显微镜明场下无法观察到的晶体双折射等光学性质.本文主要介绍几种光学显微镜在高分子结晶表征方面的应用,从光通过偏振器件及样品的角度出发,介绍偏光显微镜、PolScope系统以及Müller矩阵显微镜的基本工作原理和在高分子结晶方面的应用研究,结合具体案例,阐述这些技术如何揭示高分子晶体的微观结构,并简述一些基础的操作要点及注意事项.依据晶体的双折射特点,偏光显微镜提供了晶体厚薄、取向等结构信息和晶体生长速率等动力学信息.但是偏光显微镜的透射光强是晶体双折射和主折射率方向的方位角两者耦合的结果,而拥有可变偏振方向的PolScope系统则可以进一步精确测得双折射的光程差及晶体主折射率方向的方位角.Müller矩阵显微镜则通过检测经过样品前后的圆偏振光变化来获得样品更为丰富的光学信息,如线性双折射、圆双折射、线性二色性和圆二色性等.

Optical imaging is the simplest characterization method for observing the microscopic structures of materials in real space.Since the first one invented by Antoni van Leeuwenhoek in the 17th century,optical microscopes have found wide applications in every corner of material,chemistry and biology.Via optical microscope,we can capture micro structures invisible to naked eyes.Through polarized light,we can obtain optical properties of crystals invisible in bright field imaging.This review briefly summarizes the application of polarized optical microscopes in the characterization of polymer crystalline structures.Based on the birefringence,polarized optical microscope can reveal the structure information such as orientation of optical axes.However,polarized optical microscope only gives a coupled information of birefringence and the orientation of slow optical axis.To solve the problem,PolScope system equipped with variable direction of polarized light can determine both the optical retardance of birefringence and the azimuth of slow axis precisely.The more advanced optical microscope,Müller matrix microscope employs rotating polarization generator and analyzer to characterize more optical properties,such as linear dichroism,linear birefringence,circular dichroism and circular birefringence.Some typical applications of polarized optical microscope,PolScope system and Müller matrix microscope to characterize polymer spherulites are summarized together with the fundamentals and some using tips.