### Research

Title: Multiscale Structured Surfaces And Their Effect On Drag & Fluid Flow

Abstract:

In this thesis, we examine surface modification as a method for reducing fluid drag on a surface. Reducing drag is of great interest for many applications, including in ship construction, fluid pipelines, self-cleaning surfaces, and for use in MicroElectroMechanical Systems. Multiscale structured hydrophobic surfaces can reduce fluid drag, depending on surface chemistry and structure geometry. We examine the properties of artificial version of bio-inspired hydrophobic surfaces with multiple wetting states, including some not previously tested or known to exist.

Multiscale surfaces have structure on a small and a large scale. We evaluate the effect of changes in the large scale features on drag properties. We also vary the fluid state on the surfaces by application or removal of a passively retained secondary liquid. We examine the fluid properties in a number of ways, including torque and shear rate measurement in a custom made Cone \& Plate Rheometer.

Conventional shear rate measurements in a Cone \& Plate Rheometer depend on knowledge of the interface; since we are measuring unknown surfaces, we must develop an alternative method. We measure the components of the shear rate tensor $\mathcal{S}$ directly using Photon Correlation Spectroscopy, where we develop a general theoretical treatment for measuring 3-D flows with this technique. Previous work on Photon Correlation Spectroscopy has involved only approximate solutions, requiring free parameters to be scaled by a known case, or special cases, such as 2-D flow.

### Dissertation

### Major

Physics

### Degree

PhD