Stability of colloidal teflon dispersions in the presence of surfactants, electrolytes, and macromolecules

Abstract

A comprehensive study of the stability of colloidal polytetrafluoroethylene hydrosols in the presence of various electrolytes and macromolecular compounds is reported. Two Teflon dispersions, one containing a nonionic surfactant (Triton X-100) and the other without the surfactant, were used. Sols with small amounts of surfactant or without it behaved as typical lyophobic colloids in the presence of simple or hydrolyzed counterions. Larger amounts of Triton X-100 had a considerable stabilizing effect on these systems, which then acted as hydrophilic sols. Nonionic dextrans, dextran sulfate, and a gelatin at pH value above its isoelectric point (i.e.p.) could not flocculate either of the two Teflon dispersions. Cationic dextran (DEAE), as well as a gelatin at pH below its i.e.p., readily destabilized the sols over a narrow concentration range of the added polymers. The latter depended on the sol concentration. Positively charged macromolecules in higher concentrations exercised protective action. Finally, when gelatin was added in amounts somewhat higher or lower than the flocculation concentration at a given pH, sensitization towards the neutral electrolytes was observed.