Cohesive properties of thin films of liquids adhering to a solid surface

Abstract

The process of forming and rupturing a thin liquid film at a solid surface is described thermodynamically for both high and low energy solid surfaces. In part 1 the build-up of thin films on high-energy surfaces from the first monolayer is considered and reviewed. Components of the surface free energy of formation of the thin film (disjoining pressure) are defined. For curved surfaces the disjoining forces should be combined with the Laplace capillary pressure to give a correct form of the Kelvin equation. It is suggested from the early work of Bangham and Deryaguin that thin liquid layers have anomalous physical properties. These studies are discussed in relation to the thickness of the liquid films.

Experimental study of substrate roughness and surfactant effects on the Landau-Levich law

“…56 It is obvious that these electrical in origin forces should reveal themselves not only in the thickness of a coated film but also in its stability characteristics. Indeed, their strong effect on the film stability was found experimentally at very great thicknesses, 10 −2 cm, by the experiments of Padday 57 on film rupture and theoretically confirmed by Mitlin, 58 who described the dewetting theory in analogy with the Cahn theory of spinodal decomposition. The effect of the inclusion of aqueous salt and surfactants 57 suggests that the responsible long-range forces are electrical in origin.…”

“…Indeed, their strong effect on the film stability was found experimentally at very great thicknesses, 10 −2 cm, by the experiments of Padday 57 on film rupture and theoretically confirmed by Mitlin, 58 who described the dewetting theory in analogy with the Cahn theory of spinodal decomposition. The effect of the inclusion of aqueous salt and surfactants 57 suggests that the responsible long-range forces are electrical in origin. However, the dynamic effect on thickness of a coating film has not been studied.…”

Dip coating in the presence of a substrate-liquid interaction potential

“…9 As noted, the range of the London-van der Waals forces is typically ϳ0.03 m, whereas the interaction distance of double layers is the Debye length, l D ϳ 0.3 m. However, their strong effect on the film stability was found experimentally at very great thicknesses, 10 −2 cm, in the experiments of Padday 10 on film rupture and theoretically confirmed by Mitlin, 11 who described the de-wetting theory in analogy with the Cahn theory of spinodal decomposition. The effect of the inclusion of aqueous salt and surfactants 10 suggests that the electric double layer is the origin of the long range forces. In addition, a number of experiments indicate a strong dependence of the film thickness on the presence of a charge on a substrate: introduction of electrostatic charge on a clean glass rod by rubbing with rabbit fur 12 led to substantial deviations from theoretical predictions of Landau-Levich: the higher the charge the lower the thickness.…”

'De‐watering' capabilities of surfactants in human amniotic fluid.

“…The second stage was directed at detecting any tendency for adsorbed phospholipid monolayers to cause spontaneous rupture of a continuous supernatant fluid layer. This has been investigated using the standard method which Padday (1970) used for such surfaces as Teflon and consists of immersing the horizontal glass slide in fluid, monolayer upwards, and siphoning out the fluid until spontaneous rupture occurs or the wetted slide can be seen to emerge and distort reflexions on the liquid surface.…”

“…The critical thickness for rupture of a liquid layer adjacent to a phospholipid monolayer was determined by following the method of Padday (1970) used in the physical sciences for such purposes as studying the behaviour of fluid films covering photographic film during its development. The coated microscope slide was placed in a clean trough, levelled until perfectly horizontal, and then the trough was filled with Ringer solution to cover the slide to a depth of about 1 cm.…”