Preliminary Studies of the Influence of Forces and Kinetics on Interfacial Colloidal Assembly

Preliminary Studies of the Influence of Forces and Kinetics on Interfacial Colloidal Assembly. (August 2004) Gregory Fernandes, B.E., Mumbai University Chair of Advisory Committee: Dr.Michael Bevan In this research we illustrate how particle-particle and particle-substrate interactions affect structure in interfacial colloidal systems. A number of tools are used to quantify characteristics of deposited structures. These results help understand the effects of colloidal system interactions and deposition kinetics on the degree of ordering in interfacial colloidal structures. The first set of experiments involve 2.34 μm silica colloids interacting with silica substrates in 0mM, 5mM, 10mM, and 100mM NaCl solutions. Only the 100mM NaCl solution resulted in rapid deposition driven by van der Waals attraction, while residual electrostatic repulsion produced levitation at lower ionic strengths. This allowed direct observation of the effects of varying magnitudes of attractive interactions on interfacial colloidal structures. Rapid deposition of positively charged 1μm latex colloids on negatively charged silica substrates driven by Coulombic and van der Waals attraction produced surface structures similar to those obtained with only van der Waals attraction. Experiments on 2.34 μm silica colloids interacting with silica substrates in 10mM NaCl/pH 5.5 and 10mM NaCl/pH 10 conditions resulted in slower deposition rates. It was also found that slower deposition rates produced more compact structures displaying a higher degree of order. Another set of experiments was aimed at understanding interactions and structures formed in systems of polymerically levitated particles. Total internal reflection microscopy (TIRM) experiments revealed the influence of underlying