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Thesis (Ph.D.)--University of Delaware, 2006. / Principal faculty advisor: Mary J. Wirth, Dept. of Chemistry and Biochemistry. Includes bibliographical references.

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 ?m 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 1?m 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 ?m 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 substrate chemistry on interaction profiles in these systems. Basic experiments were also performed on the effects of varying amounts of specific ions on the dispersion stability in these systems. At conditions producing instability in polymeric systems, a similar degree of order was observed in comparison to experiments involving rapid deposition via salt addition in electrostatically stabilized systems. The results of this research clearly indicate that particle-particle and particle-substrate interactions are critical in determining structure formation by deposition. While the principal focus of this research is to study structures formed in various kinetic regimes, it also provides a basis for future studies aimed at tuning attractive interactions to produce equilibrium colloidal crystals on substrates.

The work outlined in this thesis describes how rheological techniques can be used to gain insight into the behaviour of complex hydrating systems. These techniques are currently used to elucidate interparticle interactions of concentrated colloidal dispersions. Those used here were stress relaxation, pulse shearometry and oscillation. These enabled parameters such as the dynamic moduli, relaxation moduli, relaxation spectrum and limiting moduli to be obtained. These all give a measure of the strength of interaction of the colloidal system under different conditions, without reducing these interactions by inducing flow. Calorimetric data was obtained for a hydrating cement paste. The particle and floc size of this cement was also measured. The data were found to be in accord with one another, and with current theories of the hydration processes of cement. In combination with the rheological parameters measured this enabled the extent and strength of attraction between the particles of a cement paste to be determined, as a function of the age of the paste. The adsorption characteristics of surfactant on cement were measured, as was the effect of surfactant on the particle and floc size of hydrating cement. Coupled with a measure of the rheological parameters of the cement-surfactant system, an understanding of the effect of surfactant on a hydrating cement paste was obtained. Similarly the effect of the addition of styrene-butadiene polymer latex particles, with and without excess added surfactant, was able to be determined. This information was obtained for hydrating cement pastes, both in the presence and absence of added polymer, at both ambient and non-ambient temperatures.

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