Investigations Of Colloidal Interactions

We had built up the total internal reflection microscopy (TIRM) to measure the colloidal interactions and used it to investigate the ion specificity effect shown in the colloidal interactions in low ionic concentrations. Besides, we studied the assembly and stabilization of colloidal particles at the oil-water interface, and developed a facile method to fabricate stable microcapsules based on solid particle stabilized emulsions.First, we built up the total internal reflection microscopy and wrote the signal acquisition and processing programs. This sensitive method utilizing the exponential decayed evanescent wave generated by laser total reflection at the glass-water interface. The distance of the colloid particle and the glass slide can then be deduce from the light intensity scattered in the evanescent wave field. Following the statistical thermodynamic method, we can calculate the interaction potential between the colloid particle and the surface.Then we investigated the ion specificity effect in low ionic concentrations by TIRM. We found that the interactions could be altered by the added ions in the solution. In the case of cation specificity, a V-shaped cation series is observed in terms of hm, which is attributed to the difference in the direct interactions between the cations and the sulfate groups on the particle surface, on the basis of Collins'law of matching water affinities. The cation specificity of Debye length indicates that the effective double layer thickness increases with the effective size of hydrated counterions. In the case of anion specificity, the anion sequence in terms of hm also exhibits a V-shaped series due to the accumulation or exclusion of anions near the particle surface. Moreover, the anion specificity ofκ-1 is more complex than the cation specificity because the distribution of anions in the electrical double layer is influenced by both the anion-surface and anion-cation interactions.Also we developed a simple and facile method to fabrication microcapsules template on the particle stabilized emulsion. By adjusting the composition of the phases and controlling the solution pH value, we produced stable Pickering emulsions. Then we use the solvent diffusion method to extract ethyl acetate out from the dispersed oil phase by adding water or other organic solvents. The diffusion of ethyl acetate caused the deposition of PLGA, originally dissolved in ethyl acetate, on to the interfacial adsorbed polystyrene particles. Thus the interpenetration polymer network strengthened the particle layer and stabilized the resultant microcapsules. We then studied the effect of different diffusion conditions on the structure of microcapsules by laser confocal scanning microscope and scanning electron microscope.