Assembly of colloidal crystals with well-characterized pair interaction potentials

The study of colloidal particles is of particular interest because of their applicability in photonic band-gap and sensing materials, food, and cosmetic products. The behavior of colloidal particles is difficult to predict and their phase (crystalline or amorphous) depends highly on the system. This dissertation experimentally explores the behavior of colloidal particles to understand their tunability for self-assembly applications. Using confocal laser scanning microscopy (CLSM), a direct visualization technique, we were able to understand how these colloidal particles interact with one another and self assemble crystal structures composed of oppositely-charged particles.;We developed a methodology to directly measure the pair interaction potential of colloidal particles. Working with dilute (&phis; < 0.02) colloidal suspensions, we measured the radial distribution functions using CLSM and image processing code. In conjunction with computer simulations, criteria for determining the dilute regime based on linear extrapolation of the potential of mean force to the limit of infinite dilution was developed. From this analysis, we were able to construct the pair interaction potential. Simulations were also used to understand the effect, if any, polydispersity in the experimental system would have on the proposed methodology. We found that our methodology held for polydispersities of less than 10% in the particle size.;We examined the role of sedimentation in the assembly of colloidal particles of opposite charge. Ionic colloidal crystals were successfully reproduced following the methods of Leunissen et al. The range of crystallization achievable under sedimentation was examined by varying the initial volume fraction and the density difference between the particles and solvent. We found that crystallization was achievable for medium to high initial volume fractions (&phis;i ≤ 0.12) and across all density differences studied. We compared the Peclet number as a function of the initial volume fraction to similar results for hard-sphere crystallization as reported by Davis et al. We found the trend in ionic crystallization to be opposite to that of the Davis results. We hypothesize the mechanism for ionic colloidal crystallization to not simply depend on the rate at which the particles sediment but also on the charge interactions within the system.