Swelling pressure equilibrium of physical networks in the field of an analytical ultracentrifuge

Abstract

Investigations of the swelling pressure equilibria of a physical network are performed with an analytical ultracentrifuge. The advantage of this method is that in contrast to the known swelling pressure instruments, swelling pressures in a range of composition are obtained from only a single equilibrium experiment. The Schlieren optical system of the ultracentrifuge allows the observation of the concentration gradient during the process of deswelling and swelling, and furthermore, the detection of the gel concentration at every point. The system gelatin/water shows a different behavior than that expected from the theory of Flory-Huggins for a swollen random network. The measured curves of concentration vs. the swelling pressure intersect each other in case of low initial concentrations. This shows that these networks are inhomogeneous. A new method to measure and evaluate the Schlieren pattern is described.