Wetting Phenomena on the Nanometer Scale

Nanoscale Liquid interfaces Wetting, Patterning, and Force Microscopy at the Molecular Scale 

Edited by Thierry Ondarguhu and Jean-Pierre Aime 

Macroscopically, the wetting properties of homogeneous surfaces are encoded in the equilibrium contact angle 6 a small droplet has the shape of a spherical cap, and the contact angle between the droplet surface and the substrate is independent of the droplet size (see Fig. 3.1). Young s law for this contact angle is given by the surface tensions between the fluid or and the substrate y, CTafi between the two fluids a and p, and a y between the fluid p and the substrate  

Young s law is obtained by minimizing the total free energy of the system however, more commonly it is interpreted as a statement about the mechanical equilibrium of forces of magnitudes Oay, crpy, and cTa acting along the direction of the corresponding interfaces on the three-phase contact line. The phases a and p can be vapor and liquid in the case of a liquid droplet, two liquid phases, or a liquid and a gas in the case of a gas bubble. The surface tensions depend on the combination of materials, the temperature, and the pressure. 

On the nanoscale one observes more subtle phenomena. A solid surface in contact with vapor breaks the translational invariance in the direction normal to the surface and can therefore lead to the formation of a wetting film. The thickness of such wetting 

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S. Dietrich, M. Rauscher, and M. Napiorkowski, "Wetting phenomena on the nanometer scale," in Nanoscale Liquid Interfaces Wetting, Patterning and Force Microscopy at the Molecular Scale (this issue]. 

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