Coacervation in the System Gelatin, Gelatin Derivatives, and Anionic Thickening Agents

Paper presented at a symposium on “Photographic Gelatin” organized by the Science Committee of the Royal Photographic Society on 19-22 September 1967 in Cambridge.

Abstract

The system gelatin, gelatin derivatives, and anionic thickening agents can exhibit coacervation under certain conditions. This phenomenon is marked by the appearance of opalescence and also by the inability to get a stable viscosity measurement in a rotating cylinder viscometer. It is explained on the basis of simplex coacervation. Coacervation results when the thickening agent is added to a solution of the two gelatins. Less thickener is needed to give coacervation when a higher ratio of derivatized to underivatized gelatin is used or when the derivatized gelatin has a lower isoelectric point. The lower isoelectric point is obtained by increasing the degree of derivatization or by starting with a limed ossein rather than an acid pigskin gelatin. The particular thickening agent used affects the degree of coacervation. As with simplex coacervation, pH has little effect over a moderately wide range (6-8). The derivatized gelatins by themselves, with their low content of free amino groups, are neither appreciably thickened nor coacervated by amounts of thickening agents that have marked effects on the underivatized gelatins. Although anionic at the pH of these solutions, the derivatized gelatins without anionic thickening agents do not coacervate gelatin.

Notes

Paper presented at a symposium on “Photographic Gelatin” organized by the Science Committee of the Royal Photographic Society on 19-22 September 1967 in Cambridge.