Rapid coagulation of polystyrene latex in a stopped-flow spectrophotometer

Abstract

With a stopped-flow method the rapid coagulation by electrolyte of several polystyrene latices is measured. By extrapolating back to zero time the initial process of two single particles forming a doublet is observed. We find an average rate constant ifk11 = 6.0 × 10−12 p−1 cm3 sec su−1 at 20°C, where p is the number of particles; this constant is lowered to 4.9 × 10−12 p−1 cm3 sec−1 when we assume that the particle diameters are 5% lower than the Dow values. These values are equal to 56 and 46%, respectively, of the von Smoluchowski values. Using the theory of hydrodynamic interaction, this gives Hamaker constants A = 7.0 × 10−21J or 1.5 × 10−21 J, respectively, in good agreement with theoretical predictions.