THICKENING OF ELECTROSTATICALLY STABILIZED LATICES BY ETHYL ACRYLATE METHACRYLIC-ACID COPOLYMERS WITH VARIOUS MOLECULAR-WEIGHTS

Electrostatically stabilized latices having various particle sizes wer e used to study the thickening effect of alkali-soluble ethyl acrylate - methacrylic acid copolymer (50 wt.% of the acid; <(M)over bar (W)> = 0.78 x 10(5), 4.36 x 10(5) and 11.6 x 10(5)). It was found that the effect increases with the molecular weight of the copolymers and with decreasing size of the latex particles. The pronounced tendency toward s non-bridging flocculation and phase separation suggests that the thi ckening effect of the materials results from depletion (volume restric tion) flocculation rather than depletion stabilization. The role of th e effective volume fraction of the dissolved copolymer as a variable w hich controls the rheological properties of the thickened latices was tested experimentally.