Effect of Polar-Nonpolar Additives on Oil Spreading on Solids, with Applications to Nonspreading Oils

Abstract

Nonspreading oils can be prepared from many lubricating oils by proper choice of an adsorbable additive, but an additive that makes one oil nonspreading may cause violent spreading of another. This anomalous spreading is produced by surface tension gradients resulting from adsorptive depletion of additive along the edge of the drop. Oily contamination of a surface may also cause spreading of an otherwise nonspreading oil. Since contamination rarely produces a critical surface tension above 30 dynes per cm., a practical nonspreading oil should have a surface tension above this value. Effective additives for nonspreading include the silicones, fluoroesters, amine-organic acid salts, high molecular weight organic acids, alcohols, or amines, and some oil-soluble soaps. A predeposited film of a polysiloxane prevents the spreading of most oils on metal surfaces.For an important group of applications the spreading characteristic of a lubricating oil may be as important as its viscosity, oxidation stability, or boundary lubricity. This has long been recognized by watchmakers, who require an oil that will not spread from jewel bearings to the hair spring, where it may alter the escapement rate. Jeweled bearings in meters for military electrical equipment require a similar lubricant. The nonspreading property of oil is also important because it minimizes evaporation; a drop of oil after spreading may expose as much as a thousand times the original surface. A drop of a good nonspreading oil will remain almost undiminished on a test plate for a year or more, whereas a spreading oil of equal volatility will be lost completely within one or two weeks. A spreading oil film is also undesirable

Confining Liquids on Silicon Surfaces to Lubricate MEMS

“…In the spreading tests of hexadecane blends on Si surfaces, four types of behaviours were observed, similar to those described by Cottington et al [41] for stainless steel surfaces:…”

“…It was suggested that a difference in surface tension may also play a role in this type of spreading (i.e. by the Marangoni effect) [41,43]; however, as outlined above, the additives used in this study have negligible effect on surface tension. Although remarkable, this reactive spreading is highly impractical in terms of lubricant containment and was not further pursued in this study.…”

“…4, where video frames from a test of 0.2 wt% ODA in hexadecane are shown. In this case as explained by Cottington et al [41], once the droplet is placed on the wafer, a ''foot'' or meniscus is present at its base. At this initial stage, the amine layer close to the expanding perimeter (being limited by mass transport of additive to surface) does not form densely or rapidly enough to reduce the critical surface tension of the surface below that of the solution.…”

Self-propelled running droplets on solid substrates driven by chemical reactions

“…we combine the evolution equations for the film thickness profile (11) and the field of adsorbate coverage (12) with the reaction term (14) and the disjoining pressure (13).…”

Vapor-Induced Motion of Liquid Droplets on an Inert Substrate

“…Such motion of evaporating droplets has conventionally been explained by the vapormediated Marangoni effect [3][4][5][6][7]. Liquid vapor evaporating from one droplet condenses in other droplets and changes the local composition of the droplet (see Fig.…”