Lubrication analysis of thermocapillary-induced nonwetting

Abstract

Recent interest in the phenomenon of thermocapillary-induced noncoalescence and nonwetting has produced experimental evidence of the existence of a film of lubricating gas that prevents the two surfaces in question (liquid–liquid for noncoalescence; liquid–solid for nonwetting) from coming into contact with one another. Measurements further indicate that the pressure distribution in this film creates a dimpled liquid free-surface. Lubrication theory is employed to investigate the coupled effects of liquid and gas flows for a two-dimensional nonwetting case of a hot droplet pressed toward a cold wall. The analysis focuses on the respective roles of viscous and inertial forces on droplet deformation. Resultant droplet shapes show an influence of gas viscosity maintaining nonwetting and of inertia contributing to a dimple. Previous analyses of thermocapillary-driven flow in liquid layers and droplets model the gas as purely passive which cannot be the case in the present application.

Multiscale modelling in the numerical computation of isothermal non-wetting

“…Previous simulations of the thermocapillary non-wetting problem employ simplistic models of the film region, use assumptions regarding the drop that are not relevant to proposed applications, or are unable to obtain solutions for realistic configurations. For example, the numerical simulations of and assumed a liquid free-surface shape determined by the static Young-Laplace relation to compute thermocapillary flow within the drop; the surface speed thusly obtained was used to compute the gas flow in an axisymmetric channel of constant height, as opposed to the dimpled surface measured by Dell'Aversana et al Sumner, Wood & Neitzel (2003) performed a lubrication analysis of the flows in both the liquid and gas phases, necessarily assuming a 'flat' drop instead of using a shape more relevant to the experimental work, in which the initial shape is closer to hemispherical. Chen, Kuo & Neitzel (2006) used the commercial code FIDAP to compute liquid and gas flows associated with thermocapillary non-wetting of a two-dimensional drop.…”

“…Although a two-phase lubrication analysis of the type performed by Sumner et al (2003) is also possible for this system, the present work will seek a solution that does not require a flat drop through the use of a hybrid lubrication-theory/computationalfluid-dynamics (CFD) approach. Kuo, Chen & Neitzel (2005) used their FIDAP model to compute full CFD solutions for this case, but could not obtain solutions for extremely thin lubricating films, just as in the thermocapillary non-wetting problem discussed above.…”

Thermally induced van der Waals rupture of thin viscous fluid sheets

“…For example, Schatz and Neitzel 14 reviewed experimental investigations of problems with axial temperature gradients in liquid bridges, and for driven thermocapillary waves in slots. Temperature profiles have also been utilized in the investigation of thermocapillary-induced nonwetting, 15 the fingering instability found in thin films coating a substrate, 16 and the manipulation of drops within a viscous fluid. 17 In terms of applications, ink-jet printers have become a common and economical standard for producing high-quality printed text and graphics.…”

Insights into the influence of additives on the thermal gradient induced migration of lubricant

“…9 Over the past decade, abundant correlational researches are carried out to investigate the migration mechanism and effective means to prevent the migration. [10][11][12] By painting low surface energy fluorocarbon compounds around the rubbing area, chemical gradients will be generated on the surface and the lubricant films can be confined at the desired location. 13 Surface roughness and surface topography also strongly influence on the liquid migration.…”