Theses and Dissertations

Amir Afshar

Issuing Body

Mississippi State University

Advisor

Meng, Dong

Committee Member

Elmore, Bill

Committee Member

Rai, Neeraj

Committee Member

Kundu, Santanu

Date of Degree

11-25-2020

Original embargo terms

Visible to MSU only for 2 years

Document Type

Dissertation - Open Access

Major

Chemical Engineering

Degree Name

Doctor of Philosophy

Degree Name

Doctor of Philosophy (Ph.D)

College

James Worth Bagley College of Engineering

College

James Worth Bagley College of Engineering

Department

Dave C. Swalm School of Chemical Engineering

Department

Dave C. Swalm School of Chemical Engineering

Abstract

In the atmosphere in the height of 18000ft to 25000ft, there are some metastable droplets called supercooled liquid water in the temperature range of 0◦C to 40◦C. When these droplets impinge on the wings of an airplane, a very thin layer of ice is formed on the surface. This natural phenomenon calls “impact icing”. In this research, I studied the nanoscale impact icing on structured graphite surfaces, as the substrates at the atomistic scale using Molecular Dynamics (MD) simulations. This research focuses on the first steps of the development of a predictive multiscale strategy for molecular simulations of impact ice adhesion on nanostructured substrates. Through the simulations, the molecular level physics such as molecular interactions, interfacial energy, and nanoscale surface roughness are processed into a “microscopic ice adhesion strength” that describes the energy cost for breaking the nanoscale interfacial layer. In this work, the simulation strategy is designed based on the postulate that at the nanoscale the fracture strength of impact ice on a given substrate is controlled by the extent of the ice interdigitating the substrate. The interdigitating interfacial structure is then determined by the process of wetting the substrate by a supercooled impinged water droplet and the process of penetrating of supercooled water crystallizing into ice crystals under graphene nanoconfinement. Following this line of reasoning, I divided my impact icing simulations into three separate sections including (1) simulations of dynamic wetting of supercooled water on nanostructured graphene substrate, (2) simulations of water crystallization under nano-confinement, and (3) simulations of fracture of prescribed ice-substrate interfacial structure. Based on the results, it is concluded that the degree of surface hydrophobicity, depth of penetrated water, the order of interlocked water molecules, size of surface roughness, texture structure of the surface, and ice temperature are the key roles that dominate the investigation of fracture strength of impact ice at the solid interface. Furthermore, MD simulation results demonstrate that the surface roughness lower than 3.0nm is enabled to stop water from crystallization, a piece of useful information to design anti-icing surfaces.

URI

https://hdl.handle.net/11668/20863

Sponsorship

NASA Glenn Research Center through the Advanced Aircraft Icing Subproject of the Advanced Air Transport Technology (AATT) Project (Cooperative Agreement NNX16AN20A, Richard E. Kreeger Technical Monitor)

Comments

Ice||Graphene||Fracture strength of ice||Ice crystallization||Dynamic wetting of water nanodroplet||Molecular dynamics simulation

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