Determination of the mass transport parameters in thin membranes by phase-sensitive photoacoustics in the optically transparent and mixed regimes

The research complements and extends the scope of the work reported in “LED-based multibeam photoacoustics combined with electrical circuit-based modelling for the analysis of multispecies mass transport through thin membranes” (arXiv:2602.20902). In particular, this work investigates the impact of the sample’s absorption properties on the ability to quantify slow mass transport processes in thin membranes under optically transparent and semi-opaque conditions. The theoretical framework is based on Green’s function approach as formalized by Mandelis. Owing to the separation of photoacoustic and mass transport timescales, the heat distributions are assumed to follow the temporal mass concentration profiles predicted by a Fickian diffusion process. The approach is further examined and validated using experimental data on pigment transport into a thin porous membrane. Detailed experimental results are provided in the referenced paper.