Author: Ciera Wentworth

Publisher:

Published: 2023

Total Pages: 0

ISBN-13:

Active droplets provide a rich platform for examining non-equilibrium processes of complex fluids due to simplicity of design, tunable compositions, and straightforward fabrication; and thus are suitable candidates to build upon in order to engineer responsive life-like liquid materials that can self-organize and exhibit emergent collective behaviors. Current work has focused inclusively on single droplet behaviors, pairwise interactions, and molecular solute gradients- but introducing new components or structural changes introduces new challenges creating a complex matrix of variables making it difficult to elucidate and engineering new types of active behavior. Thus, scaling to many droplets with specific organization and complex functionalities is currently out of reach. This dissertation addresses gaps in our understanding of oil-solubilization processes at the molecular level and the connection to changes in interfacial tension that govern motility at the droplet scale; elucidating such relationships will aid future research in engineering sophisticated complex fluid materials. In the work presented here, we demonstrate how non-equilibrium mass transport processes in oil-solubilizing emulsions can lead to chemorepulsive interactions--that is, droplets that are repelled by high concentrations of a chemical, as well as chemoattractive interactions--that is, droplets that are attracted by high concentrations of a chemical. The discovery of chemoattractive emulsion systems is tremendously significant as current theories surrounding active emulsions and the mechanisms of droplet propulsion cannot explain or account for attractive chemical gradients, suggesting an incomplete understanding of the molecular forces at play and necessitating a revaluation of current theories of droplet motion. The discovery of attractive droplet interactions and chemoattractive gradients creates new and exciting ways to program and tune system properties and functionalities. To gain further insight into the micellar gradients responsible for droplet motility via oil-solubilization processes, we utilize Raman MCR to characterize hydrophobic hydration changes of empty and solublilzate-filled micelles. Current solubilization-driven droplet theories focus on the mass transport process itself, but in light of chemoattractive gradients, we hypothesized solubilizate-filled micelles may provide insight into the differing interfacial tension gradients and Marangoni flows; as the hydrophobic effect plays a key role in micelle formation and oil solubilization processes. A novel Raman MCR experimental method was developed in order to investigate the changes in hydrophobic hydration of nonionic micelles before and after oil-solubilization. We find the chemical structure of the oil solubilized into the micelle has the most impact on the hydrophobic hydration, micelle size, and physical properties of the micellar solution.