Mechanics and Computation / View source

for Fundamental Atomistic Mechanisms of Capillary Flow
=Edmund Webb III, Ph.D.=
===May 24, 2012===

Fundamental Atomistic Mechanisms of Capillary Flow

Elucidating thermodynamic and kinetic properties of non-equilibrium systems remains an outstanding challenge to the science and engineering community. To pursue this challenge, our group studies canonical non-equilibrium systems: the flowing of a liquid front across a solid surface, or capillary driven wetting and spreading. Such phenomena are ubiquitous in nature as well as human technology; they can be broadly distinguished based on whether some form of chemical reaction occurs between liquid and solid during wetting. Even in cases of inert, or non-reactive, wetting, debate persists as to fundamental mechanisms by which the contact line between solid, liquid, and vapor advances; such uncertainty limits the accuracy of thermodynamic and kinetic descriptions in these non-equilibrium systems. When chemical reactions manifest along with capillary flow phenomena, the challenge to describe these systems increases, as does the opportunity to reveal intimate descriptions of complex, non-equilibrium material processes. 

In this talk, results will be presented from atomic scale simulations of what are typically called high temperature capillary systems: liquid metals flowing across solid metals. Such systems manifest throughout the materials joining realm: soldering, brazing, and welding are three processes which impact microelectronics, package sealing, and construction technological sectors, to name just a few. High temperature capillary processes also impact Earth mantle phenomena, where relevant solid/liquid interfaces are typically ceramic or metal/ceramic in composition. Data will be shown from molecular dynamics (MD) simulations of two high temperature capillary systems: one in which reactions between liquid and solid are relatively negligible and one in which they are pronounced. In the former, we examine existing theoretical descriptions for contact line advancement in non-reactive systems and determine how well observed atomistic mechanisms corroborate theory. It will be advanced that a refined constitutive description may be produced from a proper statistical interpretation of atomistic contact line behavior, obtainable from simulations. From molecular dynamics simulations of reactive wetting, we advance a rigorous thermodynamic and kinetic investigation to distinguish capillary driving forces of contact line advancement from those due to reactions between liquid and solid. It will be shown that atomic scale investigations into such systems permit quantitative distinction of the relative role of fundamental mechanisms of wetting and spreading.
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