UC Santa Barbara

Most fundamental theories on interfacial interactions consist of equilibrium phenomena, yet many processes and interactions in practice occur outside of these equilibria in a dynamic state. This thesis explores how biological and biologically-inspired surfaces and interfaces interact with each other under dynamic conditions during adhesion, friction, and lubrication. Using a surface forces apparatus, new methodologies and analyses have been designed to study such dynamic interactions. This thesis takes a tour from fully dry systems, to humidified, lubricated, and finally fully submerged systems underwater.

The chapters are divided into unique systems including gecko-inspired adhesives (Chapter 2), complex moisturizing fluids (skin creams) (Chapter 3), and lipid membranes (Chapter 4). Chapter 2 investigates the frictional adhesion characteristics of microfibrillar gecko-mimetic adhesives in diverse environments. The discovery of the underlying mechanisms for attaining grip against rough surfaces and in humid conditions has led to new design principles for future gecko-mimetic adhesives.

Chapter 3 explores how to test for and quantify high frequency dynamic friction force components in a complex lubricating film of skin cream. The instrumentation and analysis methods can be applied to any such high-speed friction experiment to uncover and unambiguously differentiate stick-slip and oscillatory friction behavior in a diverse range of systems.

Lastly, Chapter 4 discusses the discovery of dynamic lipid membrane domain rearrangements during hemifusion. New instrumentation (Fluorescence Surface Forces Apparatus – FL-SFA) was developed to simultaneously measure the interfacial forces between apposing membranes and visualize in situ morphological changes occurring at the interface. This study discovered lipid rearrangements that occur in cell-cell interactions including cellular transport. The thesis concludes with the future potential of the newly developed FL-SFA device and technique.