Diffusion kinetics of molecular probe in thin polyvinyl alcohol-based films
Researchers found that the diffusion of a molecular sample substance such as rhodamine B in polyvinyl alcohol films is significantly influenced by the type of plasticisers and surfactants added, with steric effects and intermolecular interactions playing decisive roles.
Researchers investigated the diffusion characteristics of a molecular probe in organic films of poly(vinyl alcohol) (PVA) that replicate formulations used as packaging materials. Diffusion kinetics of Rhodamine B (RhB) was measured in thin films of PVA containing glycerol and surfactants of various headgroup chemistry (cationic/nonionic/anionic) using fluorescence recovery after photobleaching and atomic force microscopy. Here we show how diffusion is determined by both molecular arrangement within the film and the nature/magnitude of intermolecular interactions.
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Addition of glycerol could improve the flexibility of PVA chains initially but imposed steric inhibition once the concentration exceeded the threshold of 44 wt%. In all investigated formulations, RhB exhibited diffusion-coupled mechanism. The presence of surfactants (at 6 wt%) reduced the diffusivity of RhB in PVA matrix for all types of surfactants used (by 30 %, 61 %, and 88 % for cationic, nonionic, and anionic surfactant addition compared to control sample, respectively). The research concludes that steric inhibition effects underpin the diffusion of RhB in PVA thin films doped with nonionic surfactant. However, for PVA films with the addition of cationic or anionic surfactant, interactions between surfactant and fluorophore are likely responsible for the change in diffusivity of the molecular probe.
Source: Progress in Organic Coatings, Volume 185, December 2023, 107833
