Continuous swelling pressure equilibria of the systemκ-carrageenan/water

Abstract

The deformation of κ-carrageenan/water gels in a centrifugal field leading to a continuous equilibrium is described. These gels form three-dimensional physical networks. The concentration gradient and the movement of the meniscus gel/solvent during the change of the concentration in the gel phase is measured with a Schlieren optical system of an analytical ultracentrifuge. The gel is considered to be a binary elastic mixture of crosslinked polymer and solvent and is assumed to remain isotropic during the deformation. The concentration dependence of the swelling pressure in the concentration range between the maximum swollen gel and that at the cell bottom can be obtained in a single equilibrium experiment. For the avaluation of the experiments, the weight fraction of the polymer in the maximum swollen gel has been determined separately by a gravimetric method.

By means of the swelling pressure-concentration curves the thermodynamic properties of the investigated κ-carrageenan/water gels can be calculated. The system can be described semi-empirically with a slightly modified Flory-Huggins equation with an interaction parameterχ _w in the weight fraction scale, which depends linearly on the concentration. The dependence of the static shear modulusG on the polymer concentration follows the scalling theory of De Gennes.