Thermodynamische Modellierung des Quellverhaltens von stimuli-responsiven Gelen in Mehrkomponentensystemen mit PC-SAFT

Abstract

Despite being versatile materials of major interest, stimuli-responsive gels have few actual application examples, due to missing insights in the thermodynamics of the response behaviour. For this reason, various experimental and theoretical investigations of the swelling behavior of poly (N-isopropylacrylamide) (PNIPAAm) gels in different solvents were carried out during this work to improve the understanding of the polymer solvent interactions. Within the experimental investigations, swelling behavior of PNIPAAm was measured in binary gel-solvent systems. Positive swelling behavior of PNIPAAm in the solvents water, butanol and acetic acid was shown. In contrast only low degrees of swelling were determined in the hydrophobic solvents hexane and butyl acetate. The reason was found in the different occurring interactions between gel and solvent. While hydrophilic solvents can form strong hydrophilic interactions with the amide groups of the gel, the weak hydrophobic interactions predominate in hydrophobic solvents. These experiments were supplemented by theoretical studies using the equation of state PC-SAFT, which was implemented and validated in Python during this work. Within these studies, a predictive utilization of the model could only be obtained for the solvents acetic acid and butanol. The swelling degree of PNIPAAm in the hydrophilic solvents generally showed very good agreement to the experimental data by adapting the binary interaction parameter. In contrast, modeling of the poor swelling behavior in the hydrophobic solvents results in greater deviations. The final application of the model to multi-component systems showed a general applicability but also the complexity of modelling polymer systems. During these investigations, the negative response behaviour of the gel with increasing hexane content of experimental data can be obtained in the simulation. Contrary to that, the model showed a trend opposite to the experimental data for increasing butyl acetate content.