Theoretical and experimental studies on heterocoagulation
Description
The purpose of this doctoral research was to pursue a better understanding of heterocoagulation When fine particles are placed in an ionic fluid medium, a two-phase system may be formed. This type of two-phase system is called colloidal dispersion. In most cases, a colloidal dispersion is thermodynamically unstable due to the tendency of the dispersed phase to minimize its surface area. Thermodynamic equilibrium between the two phases is established when the suspended particles coalesce and form a precipitate. When suspended particles are similar in surface chemical characteristics, the aggregation process is known as homocoagulation, whereas if the suspended particles are dissimilar in surface chemical nature, the process may be more accurately termed as heterocoagulation Particle encounters which may or may not result in coagulation occur due to Brownian motion and external forces. Whether coagulation takes place or not depends on the magnitude of the forces which particles exert on each other as they interact. These forces need to be understood and quantified for the purpose of explaining a macroscopic phenomenon of colloidal stability and coagulation. Since particles in a colloidal dispersion may be dissimilar in surface chemical nature, the forces of heterointeracting particles need to be understood as the forces of heterointeracting particles. Investigations were made on the forces between dissimilar particles to assess a heterocoagulation process quantitatively An algorithm to calculate the electrostatic repulsion energy between dissimilar spheres was developed. This algorithm solves the Poisson-Boltzmann equation between dissimilar plates by de-coupling the equation and estimates the spherical interaction energy using the Derjaguin method. Since a colloidal dispersion may consist of particles with different sizes, the effect of particle size distribution on the dispersion stability was investigated. The stability of polydisperse colloidal dispersion was experimentally investigated using an acoustically created n-pentadecane-in-water emulsion by a Coulter Counter. In addition, the effect of surface potential distribution was theoretically studied. Because the experimental data available on the stability of colloidal dispersion in most cases are concerned with only the onset of coagulation, viz. formation of secondary particles, an investigation was conducted on the advanced stages of coagulation of monodisperse polystyrene latices. (Abstract shortened with permission of author.)