Water Diffusion in Polymer Composites Probed by Impedance Spectroscopy and Time-Resolved Chemical Imaging

The ability to probe water diffusion in polymer composites is of significant importance for materials characterization and performance evaluation. Here, we investigate water diffusion in polymer composites using coherent anti-Stokes Raman scattering microscopy and impedance spectroscopy. Coherent anti-Stokes Raman scattering microscopy provides real-time information about evolution in the polymer composite structure during water uptake, which supports a method for evaluation of impedance data obtained in a water penetration process. The method extracts the water diffusion kinetics from the relative change in the temporal capacitance, which includes contributions from changing dielectric properties and thickness. Specifically, the method is used for investigating two model composites relevant for medical adhesives consisting of a hydrophobic and rigid polymer matrix mixed with either poly(acrylic acid) or cetyl hydroxyethyl cellulose particles. Based on our analysis, these two composites exhibit anomalous diffusion and case II sorption, respectively, corresponding to faster relaxation processes in the poly(acrylic acid) containing composites compared to the cetyl hydroxyethyl cellulose containing composites during the water uptake process. Furthermore, the cetyl hydroxyethyl cellulose containing composites demonstrate characteristic penetration and saturation times almost an order of magnitude higher than the poly(acrylic acid) containing composites. In agreement with known chemical properties of these materials, this implies a lower water affinity for cetyl hydroxyethyl cellulose compared to poly(acrylic acid).