Mass transfer kinetics inside bio-(aero)gels during solvent exchange and supercritical drying: On the relevance of advection, gel-porosity and a peculiarity regarding the tortuosity

Spatially and temporally resolved composition profiles were measured inside biopolymer gels during solvent exchange and supercritical (sc) drying using one-dimensional Raman spectroscopy. The effective diffusion co-efficients of solvent exchange and sc drying were obtained by fitting modelled composition profiles to the experimentally obtained ones. We considered one purely diffusional model, which excludes advection, and one convective model, which regards the superposition of diffusion and advection inside the pore system. The tor-tuosity was obtained by relating the obtained effective diffusion coefficients in porous media with the mutual diffusion coefficients. When considering the solvent exchange experiments the derived tortuosities for agar gels are about 1.1 and are in good agreement with literature data. When considering the sc drying experiments, the derived tortuosities are about 3.2, which is again in good agreement with literature data, but in contradiction to the tortuosities derived for the same agar gels from the solvent exchange experiments before.

Automated summary

In this study, composition profiles inside biopolymer gels during solvent exchange and supercritical drying were measured using one-dimensional Raman spectroscopy. The effective diffusion coefficients for solvent exchange and drying processes were obtained by fitting modelled profiles to experimental ones. The results showed that the tortuosities of gels varied under different experimental conditions.