Molecular migration in poly(vinyl alcohol) mixtures

Fluorescence techniques, both Fluorescence Recovery After Photobleaching and Fluorescence Correlation Spectroscopy were used to investigate the migration characteristics of small molecules in thin films composed of poly(vinyl alcohol) (PVA), glycerol and surfactants of various heasdgroup chemistry. We found that the diffusion kinetics of a molecular probe, Rhodamine B, is determined by both molecular arrangement within the film and the magnitude of charged intermolecular interactions. Addition of glycerol initially increases PVA chain flexibility, but inhibits probe movement once its concentration exceeds 44 wt% due to onset of noncompatibility between the two components. The presence of surfactants in the system was found to reduce the diffusivity of RhB in PVA matrix, which is consistent with that in bulk solutions. The reduced diffusion is likely due to steric inhibition for nonionic surfactants. However, the fine balance between inter-molecular interactions and steric inhibition governs the diffusivity of RhB when cationic or anionic surfactants are present in the matrix.