Energy requirements for stable spreading

Energy requirements for stable spreading. When a drop of a liquid is placed on the surface either of another immiscible liquid, or of a solid, it may spread to a film, or may remain as a drop without spreading. The surface tensions of the two liquids, and the interfacial tension between them, determine whether or no the liquid spreads and the same holds if the lower phase is a solid. 

Coghill and Anderson found that the angles, and probably the surface tensions, of various liquids resting on water changed with time, so that the experimental verification of Neumann s triangle was not very accurate. 

If now the surface tension of the lower liquid B increases, the angle 0A will gradually diminish until it becomes zero. At this point 

These conditions of spreading were formulated by Dupr 1 and Hardy 2 Harkins has called the difference or WiB—2yAi the spread- 

The actual form of lenses of non-spreading liquids on the surface of another immiscible liquid has been recently studied by Lyons3 and Langmuir.4 Langmuir shows that, in addition to the surface tension, if the lens is not of very large size, the linear tension / at the curved line of contact between the two liquids makes an appreciable difference to the thickness of the lens. The actual shape of the lenses is dependent on a rather complicated balance between the spreading coefficient the densities of the liquids, and the linear tension / round the perimeter of the lens, whose radius is R. If Dlt Z 2 are the densities of the lower and the upper liquids, respectively, the thickness t of a lens so large that its upper surface may be taken as flat, in the centre, is 

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