Date of Award

10-2017

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Chemical and Biomolecular Engineering

Committee Member

Dr. Sapna Sarupria, Committee Chair

Committee Member

Dr. David Bruce

Committee Member

Dr. Rachel Getman

Committee Member

Dr. Mark Roberts

Committee Member

Dr. Steve Stuart

Abstract

Heterogeneous ice nucleation is the primary pathway for ice formation. However, the detailed molecular mechanisms by which surfaces promote or hinder ice nucleation are not well understood. We present results from extensive molecular dynamics and forward flux sampling (FFS) simulations of ice nucleation near modified surfaces. The surfaces are modified to investigate the effects of different surface factors on the rate and mechanism of ice nucleation. We find that the surface charge distribution has significant effects on ice nucleation. We also investigate the interplay of surface lattice and hydrogen bonding properties in affecting ice nucleation. We find that lattice matching and hydrogen bonding are necessary but not sufficient conditions for observing ice nucleation at these surfaces. We correlate this behavior to the orientations sampled by the metastable supercooled water in contact with the surfaces. We find that ice is observed in cases where water molecules not only sample orientations favorable for bilayer formation but also do not sample unfavorable orientations. This distribution depends on both surface-water and water-water interactions and can change with subtle modifications to the surface properties. Our results provide insights into the diverse behavior of ice nucleation observed at different surfaces and highlights the complexity in elucidating heterogeneous ice nucleation. We also find that while the classical reaction coordinate of largest cluster size is a good measure of the transition between liquid water to ice, the addition of the neighboring liquid structure of the ice gives a better picture. We also have discovered that the structure of the second hydration layer gives a good representation of the reaction coordinate also.

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