Drying kinetic measurements of polymer nanolayers – Experimental results with a model-based validation and interpretation of solvent diffusion

This contribution presents a method to examine the drying process of thin films of polymer gravimetrically, ranging from a few micrometers to below 20nm using a quartz crystal microbalance (QCM). Polyvinyl acetate (PVAc) and toluene (tol) serve as the model system to validate the method by drying experiments, simulations and the determination of the concentration dependent solvent diffusion coefficient. The results show that even on the nanometer scale, the diffusion coefficient is not a function of film thickness, which is contrary to the observations that can be found in literature. A thin polymer film, still loaded with residual solvent, is placed into a flow channel with controlled drying conditions. The QCM gravimetrically measures the drying curve and precisely detects changes of mass fractions on the scale of a hundredth of a percent over the course of hours, which translates to changes in layer thickness as small as to 0.1nm per hour. The presented method is a general-purpose tool for measuring concentration-dependent diffusion coefficients, which is relevant to all sorts of thicknesses and coatings. Since nanolayers are employed, in a reasonable amount of time diffusion coefficients in the order of 10−18m2s−1 are accessible. [Display omitted] •Experimental drying curves of polymer nanolayers by quartz crystal microbalance.•Concentration dependent diffusion coefficient measurement of solvent in polymer.•Numerical simulation of polymer nanolayer drying.•Diffusion of toluene in polyvinyl acetate transferable from nanolayer to bulk.•Skin formation due to strong concentration dependency of diffusion coefficient.