Viscosimetric Determination of Latex Coagulation

Sa？etak The viscosity of latices was investigated in dependence upon the pH value of suspensions, their aging and the concentration of added electrolyte. The systems used were well-defined monodisperse polystyrene latices within the concentration range from 0.1 to 10/o, and with a high negative charge oh the latex particle surface. It was found that viscosity measurement in a dispersion at a certain concentration of the dispersed phase could be used for latex coagulation determination. On the basis of this finding an attempt was made to determine the critical coagulation concentration. The values obtained were concordant with those determined by t4rbidity measurements. In order to determine the exact pH region in which a decrease in the pH value leads to a sudden change of stability, viscosity measurements were performed in relation to the pH value of latex suspensions. The limiting pH value was independent of the time of measuring, latex concentration, and the ionic strength of the added electrolyte. In our opinion this value is characteristic of a given system and it points to the dependence of the destabilization of a dispersion on the pH value. Therefore, it can be called ？critical pH value？ by analogy to the term ？critical coagulation concen tra ti on？