Coagulation studies of polystyrene latexe

The Joyce Loebl disc centrifuge was successfully developed as a means to monitor the coagulation phenomena of 233 nm polystyrene latex. Using light scattering corrections based on Rayleigh-Gans-Debye theory, the peak areas were converted to particle number concentrations. The particle number concentrations were monitored as a function of time. Singlet-singlet, singlet-doublet, and singlet-triplet binary rate constants were derived from particle number concentration-time data using a three parameter kinetic model. The singlet-singlet and singlet-doublet Brownian coagulation binary rate constants were measured for conditions of rapid coagulation and thin double layer repulsion. The binary rate constants measured under rapid coagulation conditions are smaller than the von Smoluchowski theoretical rate constant. The discrepancy between the theoretical and experimental rate constants is attributed to viscous interactions between the colliding particles. The rate constants measured under thin double layer conditions are smaller than the rate constants obtained for rapid coagulation conditions due to the repulsive interactions of the particle double layers. Selectivity ratios based on the singlet-doublet and singlet-singlet binary rate constants suggest that hetero-coagulation is favored over homo-coagulation of the smaller particles for both rapid coagulation and coagulation in the presence of thin double layers. DLVO calculations using a spherical equivalent model for doublet particle predict a much lower selectivity ratio in the presence of the thin double layers that the experimentally observed selectivity ratio. Singlet-singlet, singlet-doublet and singlet-triplet shear coagulation binary rate constants were measured under conditions of thick double layer repulsion. The three parameter kinetic model was found to be incapable of representing the coagulation phenomena under these conditions. Particle breakup, which is not included in the three parameter kinetic model, may be responsible for the model failure. The singlet-singlet capture efficiencies showed negligible change over the range of experimental shear rates. Singlet-singlet shear coagulation binary rate constants were measured under conditions of thin double layer repulsion. Under these conditions the particles experience the coupling of Brownian and shear coagulation mechanisms. The decline of the singlet-singlet capture efficiencies with increasing Peclet numbers suggest that the coupling of the Brownian and shear coagulation mechanisms may be antagonistic at intermediate Peclet numbers.