Date of Award

2004

Document Type

Thesis

Degree Name

Master of Science in Materials Science and Engineering (MSMSE)

Department

Materials Science

First Advisor

Dr. Abdullatif Alteraifi

Second Advisor

Dr. Kamal M.S. Khalil

Third Advisor

Dr. Daniel Y. Kwok

Abstract

Classic hydrodynamic wetting theory leads to a linear relationship between spreading speed and the capillary force, being determined only by the surface tension of the liquid and its viscosity.

The theory appears in good agreement with results generated from experiments conducted on the spreading of Polydimethylsiloxanes (PDMS) on soda-lime glass substrate and fails to account for the behavior of other liquids. This thesis examines the role played by the solid substrate on the spreading kinetics of liquid droplets. The set of experiments whose results are presented below used different types of liquids with various properties of surface tension and viscosity tested on three different solid substrates (glass, polymethylmethacrylate (PMMA) and polystyrene (PS)).

The results are summed up in two themes; equilibrial spreading and kinetics. PDMS is found to exhibit complete spreading on all three different solids at similar rate for glass and PS, but at much lower rate on PMMA. Alkanes group, low surface energy liquids, was noted to exhibit equilibrial wetting that is proportional to the critical wetting energy of the solid substrate. Alcohols group, high surface energy liquids, was noted to exhibit equilibrial wetting that is inversely proportional to the wetting energy of the solids. The equilibrial spreading was found explicable on the basis of the axiom "like wets like". Contributions of the solid substrate to the spreading kinetics are attributed to specific solid-liquid interactions, of dissipative nature, which manifest itself only at the interface. The term "interfacial viscosity" is coined to account for this phenomenon.

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