Probing Differential Hydration of Poly(vinylpyrrolidone) Thin Films Using Tracer Mobility: An Insight from Fluorescence Correlation Spectroscopy

Abstract

Dynamics of small probe molecules have been routinely used to unravel the intrinsic details of charged ion transport in polymer brushes and polyelectrolyte multilayer (PEM) thin films. However, corresponding morphological properties affected with absorption of moisture have been hardly dealt with despite numerous applications of isotropic thin films in material chemistry and medical purposes. We have explored the overall structural changes associated with plasticization of PVP thin films by probing dynamics of small reporter (rhodamine 6G, Rh6G) molecules using fluorescence correlation spectroscopy (FCS). It was observed that under lesser amounts of absorbed moisture, the rigidity of the film matrix was high enough to inhibit appreciable molecular mobility. Nonetheless, with gradual increase in the moisture level within the film, molecular movement became extremely facile, so much so that it almost attained close to a solution like state. Molecular mobility was found to be dependent on both the method of preparation and the thickness of the thin films. The diffusivities mostly followed anomalous subdiffusive behaviors, reminiscent of dynamics of tracers in crowded cellular environments. The mobility was found to be independent of any electrostatic interaction between probe and polymer thin film. Hence, the tracer dynamics was attributed most likely to the viscoelasticity of the thin film matrix.

Simplifying Molecular Transport in Polyelectrolyte Multilayer Thin Films

“…[ 81,82 ] Apart from this, there are a number of other examples where transport of various other organic and inorganic dyes across PEM has been reported which have implications ranging from dye sensitized solar cells to designing smart fabrics. [ 83–87 ] By using the metal‐distant dependent fluorescence enhancement, external molecular transport of Bovine serum albumin (BSA) and Biotin in (PAH/PAA) films was performed. [ 59 ] Here, the diffusion of external molecules such as FITC‐biotin and FITC‐BSA at different incubation times, was studied in PEM films of (PAH/PAA).…”

Variable surface transport modalities on functionalized nylon films revealed with single molecule spectroscopy

“…Adsorption/desorption of the target molecules to the functionalized surface is the most desirable property to tune, but it is affected by surface irregularities, [17][18][19] inter-molecular interactions, 20 and clustering of ligands on the functionalized surface. 21,22 The surface mobility of adsorbate molecules also contributes to the heterogeneity of surface interactions and affects membrane performance.…”

Probing Bio-Molecules across Polyelectrolyte Multilayers

“…To investigate out-of-plane transport in thin polyelectrolyte multilayers, other optical techniques such as the Fluorescence Resonance Energy Transfer (FRET) and Fluorescence Correlation Spectroscopy (FCS) are better alternatives [12][13][14][15][16]. For example, out-of-plane transport of chitosan (CH) has been observed in films of CH and heparin (HEP) by using FRET [12].…”

“…Fluorescence Correlation Spectroscopy is also among the optical technique, which provides valuable information on the diffusive polymeric exchange in solution surrounding PEM stack [14][15][16]. FCS is also known as Single Molecule Confocal Microscopy as it is very sensitive to very small molecular interactions within the PEM.…”