Diffusion coefficients in polymer solutions are strongly dependent on composition and temperature. In many cases sufficient data are not available due to time-consuming measurements and a high number of material systems of interest. In this work a new method is proposed that allows determination of concentration-dependent diffusion coefficients directly from spectroscopic data of single film drying experiments. The quantitative data of concentration profiles in the sample are used to calculate diffusion coefficients by Fick's law. The results are independent of boundary conditions in the gas phase. Two polymer solutions of poly(vinyl acetate) (PVAc) and the solvents methanol and toluene are investigated. The results are compared to diffusion data from the literature. Experimental proof of the independence from boundary conditions is provided. Diffusion coefficients down to values of approximately 10 −14 m 2 s −1 are accessible. The diffusion data are in good agreement with literature data and suitable for modeling purposes.

Multicomponent diffusion of solvents in polymeric systems is not completely understood, despite many scientific contributions to the topic. Literature scarcely offers measurement data on diffusion for model validation in such systems. In this work, the ternary systems consisting of poly(vinyl acetate) and the solvents toluene and methanol was investigated experimentally and numerically. By means of inverse micro Raman spectroscopy (IMRS) concentration gradients in drying thin films have been measured. Initial composition of the samples has been varied systematically in order to detect mutual influence of the solvents' diffusive behavior. It was shown that the mobility of the different species is increased in the presence of other solvents as predicted by theory. This experimental data is provided for model validation. A new expression to calculate the diffusion coefficients in ternary mixtures is proposed which only requires binary data. This expression is tested by means of a model-based simulation to predict the drying of ternary polymer solutions in terms of concentration profiles and residual solvent content. The results are in very good agreement with the experiments. Cross terms diffusion coefficients and thermodynamic factors were not found to be necessary for a satisfying prediction.

Interdiffusion is likely to occur if two miscible polymeric films are in contact with each other in the presence of a solvent. This is e.g. relevant for the production of organic light-emitting diodes (OLEDs). Interdiffusion in OLED multilayer stacks has a great influence on the device performance. Yet, there is no study monitoring these interdiffusion processes. This is essential to gain fundamental knowledge about the predominant parameters influencing mass transfer between the present solids. In this work we demonstrate the application of inverse micro-Raman spectroscopy (IMRS) for in situ measurement of interdiffusion in polymeric multilayer systems. Interdiffusion only occurs in miscible systems, whereas no intermixing of the polymers occurs in immiscible systems. Given a miscible system, the average solvent content was found to be more important than the molecular weight of the polymers for the interdiffusion kinetics.

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Film-forming latex dispersions are an important class of material systems for a variety of applications, for example, pressure-sensitive adhesives, which are used for the manufacturing of adhesive tapes and labels. The mechanisms occurring during drying have been under intense investigations in a number of literature works. Of special interest is the distribution of surfactants during the film formation. However, most of the studies are performed at experimental conditions very different from those usually encountered in industrial processes. This leaves the impact of the drying conditions and the resulting influence on the film properties unclear. In this work, two different 2-ethylhexyl-acrylate (EHA)-based adhesives with varying characteristics regarding glass transition temperature, surfactants, and particle size distribution were investigated on two different substrates. The drying conditions, defined by film temperature and mass transfer in the gas phase, were varied to emulate typical conditions encountered in the laboratory and industrial processes. Extreme conditions equivalent to air temperatures up to 250 °C in a belt dryer and drying rates of 12 g/(m(2)·s) were realized. The surfactant distributions were measured by means of 3D confocal Raman spectroscopy in the dry film. The surfactant distributions were found to differ significantly with drying conditions at moderate film temperatures. At elevated film temperatures the surfactant distributions are independent of the investigated gas side transport coefficients: the heat and mass transfer coefficient. Coating on substrates with significantly different surface energies has a large impact on surfactant concentration gradients, as the equilibrium between surface and bulk concentration changes. Dispersions with higher colloidal stability showed more homogeneous lateral surfactant distributions. These results indicate that the choice of the drying conditions, colloidal stability, and substrates is crucial to control the surfactant distribution. Results obtained under lab-scale drying conditions cannot be transferred directly to the industrial application. The results were similar for both tested adhesive material systems, despite their different properties. This indicates that other properties, such as the particle size distribution and glass transition temperature, have surprisingly little effect on the development of the surfactant distribution.