THE SCHOOL OF MATERIALS SCIENCE AND ENGINEERING

GEORGIA INSTITUTE OF TECHNOLOGY

Under the provisions of the regulations for the degree

DOCTOR OF PHILOSOPHY

on Friday, September 27, 2019

3:00 PM

in MRDC 3403

will be held the

DISSERTATION DEFENSE

for

Andrew James Gorman

“Formation, Structure, and Reproducibility of Cerato-ulmin Hydrophobin-Coated Air Bubbles”

Committee Members:

Prof. Paul Russo, Advisor, MSE

Prof. Hamid Garmestani, MSE

Prof. Karl Jacob, MSE

Prof. Meisha Shofner, MSE

Prof. Jennifer Curtis, PHYS

Abstract:

Hydrophobins are a class of amphipathic fungal proteins with a high surface activity and high resistance to thermal and chemical degradation. These properties make hydrophobins excellent candidates for a variety of applications for coatings, drug delivery, chemical separations, and encapsulations. Cerato-ulmin (CU) is a hydrophobin produced by the two fungal species, Ophiostoma ulmi and O. novo-ulmi, known for their connection to Dutch elm disease. When an aqueous sample of CU is gently agitated, the proteins assemble into a collection of aspherical bubbles, many of them cylindrical. These large bubbles rise out of a solution due to their buoyancy but dynamic light scattering (DLS) results show remaining submicron structures remain indefinitely. These structures respond to positive and negative pressure changes both before and after initial formation suggesting that the structures are bubbles and agitating a CU solution creates a spectrum of bubbles ranging from 10-7 – 10-4 m. 

The physical characteristics of both the submicron and micron bubble films were investigated. For the submicron bubbles, small-angle x-ray scattering (SAXS) and small-angle neutron scattering (SANS) show the bubbles are cylindrical with a ~70 nm cross-sectional diameter and film thickness of 15 nm, the equivalent of 5 CU proteins. Atomic force microscopy (AFM) of collapsed microbubbles has the same film thickness suggesting that film thickness is independent of CU bubble size. To isolate singular bubble sizes during agitation, a new experimental apparatus was designed and built to agitate the CU solutions in a controlled, reproducible method. The apparatus houses a horizontal microscope for imaging CU bubbles directly after agitation and observing their motion as they rise through the solution. Results show a positive correlation with agitation frequency and bubble size, with a steady number density for all sizes up to the maximum size at that frequency value.