Crystallized surfactants are important for structured fluids, especially in consumer products such as soaps and creams. When present in sufficient concentration, surfactant crystals can interact to yield rheologically complex materials, often termed pastes. Pastes demonstrate both solid and liquid-like properties. Pastes form isotropic, space-filling networks capable of supporting their own weight. While small molecule crystallization is generally understood, crystallization of complex macromolecules requires further study. Surfactants are sufficiently complex to contain hydrophobic and hydrophilic groups, including cationic, anionic, zwitterionic, as well as nonionic head groups. Single and double tailed surfactants are common, with systematic variation in the chain length, number of double bonds, and side groups possible. The vast taxonomy of possible combinations of groups that can be assembled to form a surfactant provides a broad range of molecular interactions that can be studied with relative ease and high fidelity. A library encompassing the molecular interactions of surfactants can be systematically synthesized and the crystallization studied. A deeper understanding of the problem of surfactant crystallization can provide a database for understanding how specific intermolecular interactions affect crystallization, crystal growth, and crystal habit.

One aim of this research is to study the crystallization of a relatively unexplored, but model surfactant system. Phase diagrams will be constructed, and crystal growth rates will be measured, along with crystal habit, which will be utilized to connect crystal habit to molecular structure.

A second aim of this research is to explore the properties of dense solutions of crystallized surfactants. We propose to provide the first comprehensive understanding of the time-dependent structure-property relations underlying the thixotropic rheology of pastes comprised of crystallizing surfactants.