Miyazaki Tsukasa, Miyata Noboru, Asada Mitsunori, Tsumura Yoshihiro, Torikai Naoya, Aoki Hiroyuki, Yamamoto Katsuhiro, Kanaya Toshiji, Kawaguchi Daisuke, Tanaka Keiji
Neutron Science and Technology Center , Comprehensive Research Organization for Science and Society , 162-1 Shirakata, Tokai , Naka , Ibaraki 319-1106 , Japan.
Kurashiki Research Center , Kuraray Company, Limited , 2045-1, Sakazu , Kurashiki , Okayama 710-0801 , Japan.
Langmuir. 2019 Aug 27;35(34):11099-11107. doi: 10.1021/acs.langmuir.9b01665. Epub 2019 Aug 12.
We investigated the swelling behaviors of poly(vinyl alcohol) (PVA) films deposited on Si wafers with water vapor, which is a good solvent for PVA for elucidating structural and dynamical heterogeneities in the film thickness direction. Using deuterated water vapor, structural and dynamical differences in the thickness direction can be detected easily as different degrees of swelling in the thickness direction by neutron reflectivity. Consequently, the PVA film with a degree of saponification exceeding 98 mol % exhibits a three-layered structure in the thickness direction. It is considered that an adsorption layer consisting of molecular chains that are strongly adsorbed onto the solid substrate is formed at the interface with the substrate, which is not swollen with water vapor compared with the bulk-like layer above it. The adsorption layer is considered to exhibit significantly slower dynamics than the bulk. Furthermore, a surface layer that swells excessively compared with the underneath bulk-like layer is found. This excess swelling of the surface layer may be related to a higher mobility of the molecular chains or lower crystallinity at the surface region compared to the underneath bulk-like layer. Meanwhile, for the PVA film with a much lower degree of saponification, a thin layer with a slightly lower degree of swelling than the bulk-like layer above it can be detected at the interface between the film and substrate only under a high humidity condition. This layer is considered to be the adsorption layer composed of molecular chains loosely adsorbed onto the Si substrate.
我们研究了沉积在硅片上的聚乙烯醇（PVA）薄膜在水蒸气中的溶胀行为，水蒸气是PVA的良溶剂，用于阐明薄膜厚度方向上的结构和动力学不均匀性。使用重水蒸汽，通过中子反射率可以很容易地检测到厚度方向上的结构和动力学差异，表现为厚度方向上不同程度的溶胀。因此，皂化度超过98 mol%的PVA薄膜在厚度方向上呈现出三层结构。据认为，在与固体基板的界面处形成了一个由强烈吸附在固体基板上的分子链组成的吸附层，与上方的块状层相比，该吸附层不会因水蒸气而溶胀。该吸附层的动力学被认为比块状层明显更慢。此外，还发现了一个比下方块状层溶胀过度的表面层。与下方块状层相比，表面层的这种过度溶胀可能与表面区域分子链的更高流动性或更低结晶度有关。同时，对于皂化度低得多的PVA薄膜，仅在高湿度条件下，在薄膜与基板之间的界面处可以检测到一层溶胀程度略低于上方块状层的薄层。该层被认为是由松散吸附在硅基板上的分子链组成的吸附层。
