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Scaling down for a broader understanding of underwater adhesion
Nyarko, Alex

2018, Doctor of Philosophy, University of Akron, Polymer Science.
The design of synthetic adhesives that function efficiently in the presence of water is one of the challenging ventures in the field of adhesion. In underwater conditions, water is persistently present at the adhesive-adherend interface leading to a reduction in interfacial strength and consequent adhesive failure. The Caulobacter crescentus bacterium is known to attach irreversibly to surfaces underwater by utilizing an adhesive structure called the holdfast, which exhibits the highest adhesive energy known for any organism. Despite the impressive characteristics of the holdfast, its chemical properties still remain poorly understood.

In the first work, I employ spectroscopic techniques, including attenuated total reflection infrared spectroscopy (ATR-IR), X-ray photoelectron spectroscopy (XPS) and sum frequency generation spectroscopy (SFG) to identify the presence of a proteinaceous component of the holdfast chemistry in addition to possible surface molecules responsible for mediating adhesion at the interface. By comparing
the IR spectra of the holdfast to peptidoglycan extracts from other species, I demonstrate the similarity of the holdfast chemistry to the peptidoglycan. Knowledge
of the holdfast chemistry will provide ideas for designing synthetic underwater
adhesives, which are needed in medicine and engineering.

Even though our understanding of the holdfast chemistry has improved with these fndings, the fundamental role of water in adhesion and friction remains unclear. My work therefore investigates the effect of water on friction and adhesion at contacts between surfaces having opposite surface energies, using substrates with a gradient of wettability. We bridge macroscopic measurements with surface sensitive investigations to provide a better understanding of the effect of water on adhesion and friction. This study can serve as a guide for making surfaces which exhibit specific friction and adhesion characteristics underwater.

The final study examines the chemistry of the tree frog mucus used in wet
adhesion. Employing ATR-IR analysis, we indicate the presence of a proteinaceous
content with a close similarity in spectral profile of the toe pad and ventral skin mucus. Surface sensitive investigation shows the presence of surfactant-like molecules at the interface as well as evidence of additional moieties in the toe pad mucus as indicated by its strong surface interaction. Together, my work provides insights for the fabrication of adhesives and surfaces which are effective in underwater conditions.
Ali Dhinojwala (Advisor)
Abraham Joy (Committee Chair)
Hazel Barton (Committee Member)
Henry Astley (Committee Member)
Hunter King (Committee Member)
162 p.

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Nyarko, A. (2018). Scaling down for a broader understanding of underwater adhesion. (Electronic Thesis or Dissertation). Retrieved from https://etd.ohiolink.edu/

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Nyarko, Alex. "Scaling down for a broader understanding of underwater adhesion." Electronic Thesis or Dissertation. University of Akron, 2018. OhioLINK Electronic Theses and Dissertations Center. 18 Nov 2018.

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Nyarko, Alex "Scaling down for a broader understanding of underwater adhesion." Electronic Thesis or Dissertation. University of Akron, 2018. https://etd.ohiolink.edu/

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Full text release has been delayed at the author's request until June 01, 2023