Rheology and Microfluidic flows of a cationic surfactant and hydrotropic salt mixture

Thesis (Ph.D.)--University of Washington, 2016-08

The widespread use of wormlike micellar solutions is commonly found in household items such as cosmetic products, industrial fluids used in enhanced oil recovery and as drag reducing agents, and in biological applications such as drug delivery and biosensors. Despite their extensive use, there are still many details about the microscopic micellar structure and the mechanisms by which wormlike micelles form under flow that are not clearly understood. We focused on studying an aqueous micellar solutions of cationic surfactant cetyltrimethylammonium bromide (CTAB) and organic hydrotropic salt 3-hydroxy naphthalene-2-carboxylate (SHNC), including linear and nonlinear rheological characterizations, flow instabilities of CTAB/SHNC solution around microfluidic cylinders. The strong hydrophobicity and naphthalene structure present in the SHNC induces significant growth of CTAB wormlike micelles and promotes stable micellar network formation. We correlated its rich rheological behavior with structural transitions of the micelle network under different deformation histories and temperature variations. Since microfluidic devices provide a versatile platform to study wormlike micellar solutions under various flow conditions and confined geometry, we are able to showcase that the influence of spatial confinement and moderate hydrodynamic forces present in the microfluidic device can give rise to a host of possibilities of microstructural rearrangements and interesting flow phenomena.