聚乙烯醇(PVA)溶液凝胶化过程中的动力学和结构演化规律

Polarizing films, as indispensable components for display,play a decisive role in image quality, whereas the polarizing films utilized in China relies entirely on imports.The key technology to be broken through in the PVA films industry is to suppress fluctuation of the film thickness during processing, thereby ensuring the structural and optical uniformity of the base films. Whether uniform films can be obtained mainly depends on two aspects, the thixotropic properties, as well as the interplay between crystallization and phase separation during the gelation of PVA. A lot of studies have been placed on the rheological properties of the PVA solution under the steady shear.However, it remains unclear how to achieve significant thixotropic properties, as well as the regulation and control of the microstructure during the gelation of PVA. In this project, we propose to investigate the thixotropic properties of PVA solution and explore the essential mechanism of thixotropy by means of rheological, rheological optical microscope and diffusion wave spectrum (DWS), In addition, we will explore the interplay between crystallization and phase separation in the gelation process, and establish the correlation between kinetics of the phase separation, crystal growth and the evolution of linear viscoelasticity, which is expected to provide knowledge for fabricating PVA films with well-tailored structure, thereby improving properties of the final optical films.

偏光膜（聚乙烯醇（PVA）膜）是决定显示质量的关键材料，我国的偏光膜材料完全依赖于进口，在PVA膜生产制造中，如何抑制膜厚波动，保证基膜结构及光学均匀性是我国独立自主生产PVA膜急需突破的关键技术。能否实现均匀成膜， 一方面由溶液的触变行为控制；另一方面，由于PVA是一种结晶高分子，成膜结构由凝胶化过程中结晶与微相分离二者的相互作用控制。目前，对于PVA体系的研究侧重于稳态剪切流场下PVA溶液的流变行为，对于如何实现显著的触变性和如何调控凝胶化过程中微相结构仍缺乏清楚的了解。本项目拟通过流变学，流变-光学显微镜连用以及扩散波谱（DWS）等方法，探索引起触变行为的机理，探究PVA溶液凝胶化过程中的相分离结构、结晶结构与线性粘弹性之间关联性，发展适用于调控结晶和相分离二者相互作用的相关物理参数，进而为偏光膜加工参数的选择提供理论依据。

聚乙烯醇（PVA）水溶液体系在纤维纺丝、水凝胶及PVA薄膜成形方面有较多应用。PVA水溶液凝胶化过程是一个复杂的动力学和结构演化过程，对此过程的研究可以为溶液加工过程提供理论参考。本项目针对PVA溶液凝胶化过程中结晶，微相分离和逾渗网络等不同尺度的结构形成及机制等核心问题，研究了无流场条件下，PVA溶液凝胶过程中的相分离结构、晶体结构与线性粘弹性之间关联性，构建PVA溶液凝胶化的浓度-温度二维相图；通过对PVA溶液施加剪切速率大于分子链拉伸所需的临界剪切速率（Rouse松弛时间的倒数）的剪切流场作用，诱导溶液中结晶预有序体的形成，同时阐明了结晶预有序体具有可逆物理交联网络结构特征；在此基础上，通过溶液剪切结合冷冻技术实现诱导溶液体系中晶体的直接形成；为有效控制PVA溶液凝胶化过程中结晶和相分离二者相互作用相关物理参数的选择提供指导。