Layered Structure in the Crystalline Adsorption Layer and the Leaching Process of Poly(vinyl alcohol) Revealed by Neutron Reflectivity

Abstract

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.

Investigation of Interfacial Water Accumulation between Polypropylene Thin Film and Si Substrate by Neutron Reflectivity

“…The adsorption layer is strongly constrained on a substrate and remains on the substrate even after immersion in a good solvent. Many studies have been performed on the structures and growth kinetics of adsorption layers for various amorphous polymers. − The adsorption layers of crystalline polymers could grow on solid substrates in the same manner as that of amorphous polymers. − In this study, it is considered that a PP adsorption layer was grown on a Si substrate when a hot p -xylene solution of PP was deposited on the substrate heated at 200 °C prior to spinning of the substrate in the spin-coating procedure or during drying after the deposition. The growth of the adsorption layer indicates that the polymer chains of PP are physically in close contact with the substrate, and there are no distinct water-includable spaces at the interface between the PP film and substrate.…”

“…The structural parameters are also listed in Table S1 as the fitting results. The thickness, SLD, and interfacial roughness of the native oxide layer are determined to be 1.0 nm, 3.3 × 10 –4 nm –2 , and 0.5 nm, respectively, as shown in Table S1. ,,− These parameters of the Si substrate were fixed in the subsequent best fitting procedures of the NR profiles for PP thin films in vacuum and at the saturated vapor pressure of water. These parameters were also used to determine the concentration profiles of deuterated water at the interfaces between the PP films and the substrate.…”

Neutron Reflectivity Study on the Suppression of Interfacial Water Accumulation between a Polypropylene Thin Film and Si Substrate Using a Silane-Coupling Agent

“…Figure S2 in the Supporting Information shows the XRR measurements for the untreated Si wafer, which had a thin, native oxide layer on the surface. In our previous study, the Si substrate employed in this study was structurally characterized using NR, and the SLD and thickness were determined to be 3.3 × 10 –4 nm –2 and 1.0 nm, respectively. ,− XRR can also be used to characterize the native oxide layer, although the thickness and density are much less accurate than those determined using NR owing to the low contrast between the native oxide layer and bare Si underneath. The solid line in Figure S2 indicates the best-fitted result obtained using a single-layer model to describe the native oxide layer on Si.…”

A Model for the Structure of Adsorbed Layers at Solid/Liquid Interfaces

“…Many techniques such as small-angle neutron scattering (SANS), − neutron reflectivity (NR), − ellipsometry (EM), atomic force microscopy (AFM), dual polarization interferometry (DPI), ultracentrifugation (UC), and photon correlation spectroscopy (PCS) − have been used to estimate the structure of adsorbed layers at solid/liquid interfaces. Interestingly, Nagy suggested a “sorbent mass variation” (SMV) method for determining the composition and thickness of adsorbed layers, only from the isotherm data obtained by simple adsorption measurements. − We previously studied the adsorption of benzyldimethyldodecylammonium bromide (BDDABr) at SiO 2 /H 2 O interfaces using the SMV method, affording information about the structure of adsorbed layers .…”