TY - JOUR
T1 - Detailed Structural Study on the Poly(vinyl alcohol) Adsorption Layers on a Si Substrate with Solvent Vapor-Induced Swelling
AU - Miyazaki, Tsukasa
AU - Miyata, Noboru
AU - Yoshida, Tessei
AU - Arima, Hiroshi
AU - Tsumura, Yoshihiro
AU - Torikai, Naoya
AU - Aoki, Hiroyuki
AU - Yamamoto, Katsuhiro
AU - Kanaya, Toshiji
AU - Kawaguchi, Daisuke
AU - Tanaka, Keiji
N1 - Funding Information:
Neutron reflectivity measurements were performed on BL17 at the Material and Life Science Experimental Facility of J-PARC (Japan) under Program Nos. 2018C0006 and 2019C0003. This work was supported by the JST-Mirai program (Japan) under Grant No. JPMJMI18A2.
Publisher Copyright:
Copyright © 2020 American Chemical Society.
PY - 2020/4/7
Y1 - 2020/4/7
N2 - We investigated in detail the structures in the poly(vinyl alcohol) (PVA) adsorption layers on a Si substrate, which remained on the substrate after immersing the relatively thick 30-50 nm films in hot water, by neutron reflectometry under humid conditions. For the PVA with a degree of saponification exceeding 98 mol %, the adsorption layer exhibits a three-layered structure in the thickness direction. The bottom layer is considered to be the so-called inner adsorption layer that is not fully swollen with water vapor. This may be because the polymer chains in the inner adsorption layer are strongly constrained onto the substrate, which inhibits water vapor penetration. The polymer chains in this layer have many contact points to the substrate via the hydrogen bonding between the hydroxyl groups in the polymer chain and the silanol groups on the surface of the Si substrate and consequently exhibit extremely slow dynamics. Therefore, it is inferred that the bottom layer is fully amorphous. Furthermore, we consider the middle layer to be somewhat amorphous because parts of the molecular chains are pinned below the interface between the middle and bottom layers. The molecular chains in the top layer become more mobile and ordered, owing to the large distance from the strongly constrained bottom layer; therefore, they exhibit a much lower degree of swelling compared to the middle amorphous layer. Meanwhile, for the PVA with a much lower degree of saponification, the adsorption layer structure consists of the two-layers. The bottom layer forms the inner adsorption layer that moderately swells with water vapor because the polymer chains have few contact points to the substrate. The molecular chains in the middle layer, therefore, are somewhat crystallizable because of this weak constraint.
AB - We investigated in detail the structures in the poly(vinyl alcohol) (PVA) adsorption layers on a Si substrate, which remained on the substrate after immersing the relatively thick 30-50 nm films in hot water, by neutron reflectometry under humid conditions. For the PVA with a degree of saponification exceeding 98 mol %, the adsorption layer exhibits a three-layered structure in the thickness direction. The bottom layer is considered to be the so-called inner adsorption layer that is not fully swollen with water vapor. This may be because the polymer chains in the inner adsorption layer are strongly constrained onto the substrate, which inhibits water vapor penetration. The polymer chains in this layer have many contact points to the substrate via the hydrogen bonding between the hydroxyl groups in the polymer chain and the silanol groups on the surface of the Si substrate and consequently exhibit extremely slow dynamics. Therefore, it is inferred that the bottom layer is fully amorphous. Furthermore, we consider the middle layer to be somewhat amorphous because parts of the molecular chains are pinned below the interface between the middle and bottom layers. The molecular chains in the top layer become more mobile and ordered, owing to the large distance from the strongly constrained bottom layer; therefore, they exhibit a much lower degree of swelling compared to the middle amorphous layer. Meanwhile, for the PVA with a much lower degree of saponification, the adsorption layer structure consists of the two-layers. The bottom layer forms the inner adsorption layer that moderately swells with water vapor because the polymer chains have few contact points to the substrate. The molecular chains in the middle layer, therefore, are somewhat crystallizable because of this weak constraint.
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U2 - 10.1021/acs.langmuir.9b03964
DO - 10.1021/acs.langmuir.9b03964
M3 - Article
C2 - 32176499
AN - SCOPUS:85083041400
VL - 36
SP - 3415
EP - 3424
JO - Langmuir
JF - Langmuir
SN - 0743-7463
IS - 13
ER -