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Colloidal suspensions transform between fluid and disordered solid states when parameters such as the colloid volume fraction and the strength and nature of the colloidal interactions are varied. Seemingly subtle changes in the characteristics of the colloids can markedly alter the mechanical rigidity and flow behavior of these soft composite materials. This sensitivity creates both a scientific challenge and an opportunity for designing suspensions for specific applications. In this work, we investigate how the mechanical properties of thermo-reversible gels composed of octadecyl silica particles in decalin (sizes varying between 18 nm and 185 nm), at moderate particle concentrations change as a function of strength of attraction and particle loading. We further test the limits of applicability of scaling criteria developed within the framework of percolation theories and the more recently developed mode coupling theories. By using the experimentally measured gel boundaries and elastic moduli, the strength and range of attraction between the particles were obtained by comparison with the naïve mode coupling theory (NMCT) assuming a Yukawa interaction potential. We find reasonable agreement between theory and experiment when the data are scaled according to the relations proposed by percolation models for individual particle sizes, however these models fail to collapse the elastic moduli and yield stress data onto universal scaling curves for the entire range of particle sizes studied. The naïve mode coupling theory framework however does a remarkable job at predicting the gel boundaries, elastic moduli and the yield stresses. Finally, scaling relations are developed that collapse the elastic moduli and yield stress data onto master curves for all particle sizes and particle concentrations examined in this study.
A Thesis submitted to the Department of Chemical and Biomedical Engineering in partial fulfillment of the requirements for the degree of Master of Science.
Includes bibliographical references.
Subramanian Ramakrishnan, Professor Directing Thesis; John C. Telotte, Committee Member; Sachin Shanbagh, Committee Member.
Florida State University
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