Adsorption of Poly(Vinyl Alcohol) from Water to a Hydrophobic Surface:  Effects of Molecular Weight, Degree of Hydrolysis, Salt, and Temperature

Abstract

The adsorption of poly(vinyl alcohol) (PVOH) from aqueous solutions to a silicon-supported fluoroalkyl monolayer is described. Thickness, wettability, and roughness of adsorbed films are studied as a function of polymer molecular weight, degree of hydrolysis (from the precursor, poly(vinyl acetate)), polymer concentration, salt type and concentration, and temperature. The data suggest a two-stage process for adsorption of the polymer: physisorption due to a hydrophobic effect (decrease in interfacial free energy) and subsequent stabilization of the adsorbed layer due to crystallization of the polymer. Adsorption of lower-molecular-weight polymers results in thicker films than those prepared with a higher molecular weight; this is ascribed to better crystallization of more mobile short chains. Higher contents of unhydrolyzed acetate groups on the poly(vinyl alcohol) chain lead to thicker adsorbed films. Residual acetate groups partition to the outermost surface of the films and determine wettability. Salts, including sodium chloride and sodium sulfate, promote adsorption, which results in thicker films; at the same time, their presence over a wide concentration range leads to formation of rough coatings. Sodium thiocyanate has little effect on PVOH adsorption, only slightly reducing the thickness in a 2 M salt solution. Increased temperature promotes adsorption in the presence of salt, but has little effect on salt-free solutions. Evidently, higher temperatures favor adsorption but cause crystallization to be less thermodynamically favorable. These competing effects result in the smoothest coatings being formed in an intermediate temperature range.

Poly(Vinyl Alcohol) Physical Hydrogels: New Vista on a Long Serving Biomaterial

“…This, in turn, implies that thicker PVA coatings are less crystalline, an assumption which was verified by ATR IR spectra of the films. In a follow‐up study,126 adsorption of aqueous PVA onto silicon‐supported fluoroalkyl monolayers was investigated in detail with regard to the effects of molecular weight, degree of hydrolysis, concentration of kosmotropic salts and temperature on the thickness, wettability and roughness of the adsorbed layers. Supporting the original findings, increased polymer concentration produced polymer coatings with increased thickness, a phenomenon observed on polymer samples with molecular weights 14, 89 ÷ 98 and 124 ÷ 186 kDa, Figure 7A.…”

“…Polymer adsorption is further facilitated by increased concentrations of kosmotropic salts (C: ○: NaCl; ▪: Na 2 SO 4 ; ▵: NaSCN). Images A–C reprinted with permission,126 Copyright 2004, American Chemical Society. Adsorption of PVA is also supported by dehydrated PVA surfaces thus allowing for multiple sequential adsorption steps and a build‐up of films with controlled thickness, the latter being further controlled by the presence of sodium chloride (D: (a) 2 M ; (b) 1.5 M ; (c) 1 M ; (d) 0 M .…”

Hindered diffusion of proteins and polymethacrylates in controlled-pore glass: An experimental approach

“…The synthetic polymer does not seem to interact too much with the solid, as the low values of K show. In any case there seems to be a higher interaction when the molecule is smaller, as it has a higher surface per unit volume available of interaction with the solid surface (Kozlov and McCarthy, 2004). Proteins are known to adsorb in a variety of solids due to their complex nature and the value of this constant is usually higher than that of other polymers with weaker interactions, like PMA.…”

On the stability of the polymer brushes formed by adsorption of Ionomer Complexes on hydrophilic and hydrophobic surfaces

“…12b). The stability of this C3M layer on polysulfone may be explained by the high affinity of the poly(vinyl alcohol) to hydrophobic surfaces [44][45][46][47]. We believe that C3M-PVA 445 /P2MVPI 228 most probably does not unfold upon adsorption on a hydrophobic substrate, but rather adsorb via the PVA corona chains.…”