Miyazaki Tsukasa, Miyata Noboru, Arima-Osonoi Hiroshi, Kira Hiroshi, Ohuchi Keiichi, Kasai Satoshi, Tsumura Yoshihiro, Aoki Hiroyuki
Neutron Science and Technology Center, Comprehensive Research Organization for Science and Society, 162-1 Shirakata, Tokai, Ibaraki 319-1106, Japan.
Kurashiki Research Center, Kuraray Co., Ltd., 2045-1, Sakazu, Kurashiki, Okayama 710-0801, Japan.
Langmuir. 2021 Aug 17;37(32):9873-9882. doi: 10.1021/acs.langmuir.1c01563. Epub 2021 Aug 4.
We investigated the structure of the crystalline adsorption layer of poly(vinyl alcohol) (PVA) in hot water by neutron reflectivity in two cases: when the adsorption layer is exposed on the substrate by leaching the upper bulk layer and when it is deeply embedded between a relatively thick PVA film and substrate. In both cases, the PVA adsorption layer consists of three layers on the Si substrate. The bottom layer, consisting of amorphous chains that are strongly constrained on the substrate, is not swollen even in hot water at 90 °C. The middle layer, consisting of amorphous chains that are much more mobile compared with those in the bottom layer, has no freedom to assume a crystalline form. Only the molecular chains in the top layer are crystallizable in the adsorption layer, leading to a heterogeneous layered structure in the film thickness direction. This layered structure is attributed to the crystallizable chains of PVA during the formation of the adsorption layer driven by hydrogen bonding. However, the structure and dynamics in the adsorption layer may differ in both cases because the molecular chains in the vicinity of the surface seem to be affected by surface effects even in the adsorption layer.
我们通过中子反射率研究了热水中聚乙烯醇（PVA）晶体吸附层的结构，研究了两种情况：一种是通过浸出上层本体层使吸附层暴露在基底上，另一种是将其深埋在相对较厚的PVA薄膜和基底之间。在这两种情况下，PVA吸附层在硅基底上均由三层组成。底层由在基底上受到强烈约束的无定形链组成，即使在90℃的热水中也不会溶胀。中间层由比底层的链更具流动性的无定形链组成，没有形成晶体形态的自由度。只有顶层中的分子链在吸附层中可结晶，从而在膜厚方向上形成异质层状结构。这种层状结构归因于在氢键驱动的吸附层形成过程中PVA的可结晶链。然而，这两种情况下吸附层的结构和动力学可能不同，因为即使在吸附层中，表面附近的分子链似乎也受到表面效应的影响。
