AGGREGATION STABILITY AND ELECTROSURFACE PROPERTIES OF A UREA-MODIFIED SILICA

The introduction of urea increases the aggregation stability of the si lica hydrosol over a wide pH range. Additional lyophilization of the s ol in the acid region is observed in spite of the neutralization of th e surface charge and in the alklaine region there are simultaneous inc reases in the surface charge density and electrophoretic mobility. The aggregation stability of sols modified with urea has been shown to in crease as the electrolyte is added. The lyophilization effect of urea is explained in terms of the formation of a boundary liquid layer on t he silica particles that is unable to dissolve electrolytes. When cons idering the aggregation stability of modified silica sols the structur al component of the disjoining pressure must be taken into account bot h in the acid and alkaline pH regions.