Structural Evolution of Thin Polystyrene Films after solvent/non-solvent treatment

本论文以聚苯乙烯薄膜为研究对象,研究应用溶剂/非溶剂连续处理而改变聚苯乙烯薄膜结构的方法。首先采用旋转涂膜法制备聚苯乙烯薄膜，利用谱学椭圆偏振仪、同步辐射掠入射超小角X射线散射与X射线反射方法来联合测定薄膜性质，进行了以下实验： 一． 离线实验：聚苯乙烯的四氢呋喃溶液在经亲水性预处理的硅片基底上旋转涂膜，退火后，聚苯乙烯薄膜连续浸入其溶剂N,N-二甲基甲酰胺与非溶剂乙醇，经过溶胀和沉淀过程，彻底改变了原来薄膜的表面结构，原子力显微镜和掠入射小角X射线散射在薄膜表面实验结果清晰显示，薄膜表面形成了不同尺度的聚苯乙烯聚集体，。结果表明同步辐射掠入射小角X射线散射是一种新颖，简单易行的观察薄膜表面结构的强有力的手段。溶剂/非溶剂处理聚苯乙烯表面的方法简便易行，是一种非常有潜力的改善聚苯乙烯表面结构的方法。 二． 在线实验：根据离线实验结果，自行设计制造了一个椭圆偏振仪样品池，用椭圆偏振仪上在线跟踪气态溶剂/非溶剂处理聚苯乙烯薄膜，努力追踪溶剂/非溶剂处理聚苯乙烯薄膜过程中，薄膜结构的动态变化规律。结果显示，气态溶剂/非溶剂处理薄膜表面的结果与用液态溶剂/非溶剂处理的结果不同，处理后的薄膜表面性质没有明显改变，而且加入非溶剂后椭偏参数随时间的一级指数衰减与膜厚成线性关系。原因可能是样品池内为混合气体，非溶剂蒸汽压不够，不足以引起聚苯乙烯分子链的沉淀，溶胀的薄膜又回复原态。In this thesis, we studied a new method to improve the surface structure of polystyrene films. The polystyrene films were treated with solvent/nonsolvent sequence. The films were made by spin-coating and studied by ellipsometry, grazing incidence ultra-small-angle X-ray scattering (GIUSAXS), X-ray reflectivity and atomic force microscopy (AFM): The films were treated with liquids of solvent/non-solvent sequence resulting in a process of swollen and precipitation of the polystyrene film. Such a treatment destroyed completely the original surface structure of the film. Aggregates of polystyrene of different size were observed both in atomic force microscopy and synchrotron grazing incidence ultra-small angle X-ray scattering measurements. The results demonstrate that synchrotron grazing incidence ultra-small angle X-ray scattering is a unique, easy to use and powerful means to investigate the structural features of thin films supported onto smooth surfaces. The method of treating polystyrene film with solvent/non-solvent is easy and has the potential to be used in industry. Furthermore, we designed and constructed an ellipsometric sample cell to trace the kinetic process of structural evolution of polystyrene films after solvent/nonsolvent treatment. The results showed that treating with vapor of solvent/non-solvent is different from treating with liquids. The character of polystyrene films after the solvent/non-solvent vapor treatment hardly changed compared with the initial film. From a swollen state, these polystyrene films were able to recover to their initial state after treated by the non-solvent vapor. During such a shrinking process, one observed an exponential decay of the ellipsometric parameter (Is,Ic). The characteristic decay time is propotional to the thickness of the films. This is due to that the gas in the cell is a mixture and the pressure of the nonsolvent is not high enough to induce the precipitation of the polystyrene chains. The swollen films therefore reverted to the initial state after treatment