Molecular mechanisms during the thermoreversible gelation of gelatin-water-systems

Abstract

A dynamic viscometer is presented that enables the determination of the complex shear modulus and the optical rotation of systems during the process of thermoreversible gelation. It is demonstrated that the storage and loss modulus during an oscillating shear deformation can be obtained from the ratio of the amplitudes and the phase shift of the signals due to the driving external momentum and the response of the deformation. — Results of measurements of the optical and rheological properties of the system gelatin-water with a polymer content of 2.94% by wt. after a temperature step to the transformation range are reported. From the time dependence of the physical quantities it is deduced that the first process is followed by an increase of the viscosity and can be related to the formation of macromolecular clusters. Finally, the storage modulus develops as a function of time, indicating the formation of an infinite molecular network. Near the gel point the results agree well with the predictions of the percolation theory, whereas in the subsequent range of gelation a kinetic approach has been discussed to describe the results.

Extended version of the oral presentation at the Kolloid-Tagung in Bochum 1989.