Abstract

Adhesion and dissipation during surface interactions are important phenomena with wide applications in materials science, including cold-spray technology for additive manufacturing and stiction in MEMS (Mircro ElectroMechanical Systems). In planet formation theories, energy dissipation in collisions between mineral grains is important to the formation of dust-grain aggregates and planetesimals. Early contact mechanics theories such as Hertz and Johnson-Kendall-Roberts have laid theoretical foundations for understanding these phenomena. Recently, there are breakthroughs in using non-equilibrium thermodynamics methods to elucidate dissipation. For example, the Green-Kubo method can calculate transport coefficients based on the Fluctuation-Dissipation theorem, and Jarzynski equality can be used to determine reversible free energy curves and dissipative work. This work develops simulation methods and applies molecular-dynamics, based on empirical potentials, to address adhesion and dissipation. It will be shown here that in collisions between amorphous wustite nanoparticles, strong dissipation occurs with large deformation, structural reordering, and changes in atomic coordination numbers. It will also be demonstrated here that passivation by dissociated water molecules on silica surfaces strongly decreases dissipation and adhesion. Green-Kubo methods used to calculate dissipation in forsterite slabs' interactions is found to suffer from extremely long correlation times. By contrast, an approach previously employed to model atomic-force-microscopy, when used with the Jarzynski equality, demonstrates that transitions of ions between metastable states, especially in defective surfaces, are responsible for dissipation in a manner similar to stick-slip behavior in friction studies. Finally, as this work shows the role of chemical modifications to surfaces, there is a need to go beyond empirical potentials to Density-Functional-Theory models with chemical accuracy, and this work outlines, tests and verifies such a multiscale modeling approach.

Notes

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Graduation Date

2021

Semester

Fall

Advisor

Schelling, Patrick

Degree

Doctor of Philosophy (Ph.D.)

College

College of Engineering and Computer Science

Department

Materials Science and Engineering

Degree Program

Materials Science and Engineering

Format

application/pdf

Identifier

CFE0008825; DP0026104

URL

https://purls.library.ucf.edu/go/DP0026104

Language

English

Release Date

December 2022

Length of Campus-only Access

1 year

Access Status

Doctoral Dissertation (Campus-only Access)

Restricted to the UCF community until December 2022; it will then be open access.

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