The atomistic mechanism of high temperature contact line advancement: results from molecular dynamics simulations

Y Sun and EB Webb, JOURNAL OF PHYSICS-CONDENSED MATTER, 21, 464135 (2009).

DOI: 10.1088/0953-8984/21/46/464135

Atomic scale phenomena driving contact line advancement during the wetting of a solid by a liquid are investigated via molecular dynamics simulations of Ag(1) drops spreading on Ni substrates. For the homologous temperature similar to 5% above melting for Ag, essentially non-reactive wetting is observed with relatively high spreading velocity. Analyzing atomic positions with time, including computing flow fields, permits investigation of atomic scale transport mechanisms associated with advancement of the contact line. Delivery of material to the contact line occurs preferentially along the liquid/vapor interface. Ag(1) atoms transported along the liquid/vapor interface become new droplet edge material, effectively displacing existing edge material. Evidence is also shown of a prominent transport and flow mechanism more typically associated with the molecular kinetic theory of spreading: some portion of Ag(1) atoms move along the solid/liquid interface to eventually occupy the contact line region. Selected atomic trajectories are shown to illustrate atoms moving with the contact line, detaching and re-attaching at sites along the solid/liquid interface. However, this latter solid/liquid interface transport mechanism contributed a lower percentage of new material to the advancing contact line compared to the liquid/vapor interface transport mechanism. Features of the AgNi system that may contribute to the dominance of a liquid/vapor interface transport mechanism are highlighted, including a relatively low liquid/vapor surface tension.

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