Department of Materials Science and Engineering, POSTECH, Pohang-city, Gyeongbuk, South Korea.
Langmuir. 2010 Dec 7;26(23):18483-90. doi: 10.1021/la1035085. Epub 2010 Nov 10.
The diffusion processes of water molecules into polymer films (PMMA/PS homopolymers and random copolymers) in contact with liquid water were investigated using gravimetric methods and X-ray reflectivity (XRR) analysis. Methods of water contact and XRR measurement were designed for studying the systems in the nonequilibrium state of diffusion. Gravimetric measurements confirmed the Fickian diffusion behavior of films in contact with water. Vertical density distributions in PMMA and methylmethacrylate-rich copolymer films demonstrate the existence of a water-rich layer at the interface. However, with further absorption of water into the film, the overall density increased throughout the film. The results suggest that the diffusion of water into the polymer film occurs to recover density uniformity with a high concentration of water molecules at the surface. Some XRR data for the PS- and styrene-rich copolymer films could not be fit and converted to a vertical density distribution because of their huge diffusion coefficients. However, the reflectivity curves for these films and the vertical density distribution after sufficient water contact suggested that the surfaces of these films were commonly diffused after water contact. Atomic force microscopy (AFM) analysis demonstrated that the surface roughness of these films actually increased with water content.
采用重量法和 X 射线反射（XRR）分析研究了与液态水接触的聚合物膜（PMMA/PS 均聚物和无规共聚物）中水分子的扩散过程。设计了水接触和 XRR 测量方法来研究扩散非平衡状态下的体系。重量法测量结果证实了膜与水接触时的菲克扩散行为。PMMA 和甲基丙烯酸甲酯富共聚物膜的垂直密度分布表明在界面处存在富水层。然而，随着水进一步吸收到膜中，整个膜的整体密度增加。结果表明，水向聚合物膜的扩散是为了恢复密度均匀性，在表面处具有高浓度的水分子。由于 PS 和苯乙烯富共聚物膜的一些 XRR 数据的扩散系数非常大，因此无法拟合和转换为垂直密度分布。然而，这些膜的反射率曲线以及充分水接触后的垂直密度分布表明，这些膜的表面在水接触后通常会发生扩散。原子力显微镜（AFM）分析表明，这些膜的表面粗糙度实际上随含水量的增加而增加。
