Poly(vinyl alcohol)film formation process using single-sided low-field NMR relaxometry: effect of initial concentration

Abstract

The film formation of Poly(vinyl alcohol) (PVOH) from water solutions of different concentrations has been studied using a low-field, single-sided nuclear magnetic resonance (NMR) scanner. The film formation takes place during the drying of a cast polymer solution under controlled environmental conditions. The NMR scanner allows a vertical (depth) resolution of 50μm up to the formation of the final film of typically 300μm thickness. A depth-dependence of the relaxation time T2 was found as a signature of dynamic heterogeneities in the drying process under which the film is gradually forming. The difference in the dynamics at different heights suggest an increase of local molecular order which is more pronounced towards the air/film interface, for all initial concentrations of the polymer solutions. The relaxation profiles indicate that the onset of dynamical heterogeneity appears at PVOH concentration larger than 25% in all samples.