Equilibrium configurations of liquid droplets on solid surfaces under the influence of thin-film forces Part I. Thermodynamics

We present a rigorous thermodynamic analysis of single-component, two-dimen sional (cylindrical) and three-dimensional (axisymmetric) drops and bubbles on an ideal solid substrate when the drop or bubble is subject to thin-fil m forces. Minimization of the system isothermal Helmholtz free energy yield s the classic augmented Young-Laplace differential equation describing drop let shape. Attendant boundary conditions emerge naturally including a new a ugmented Young relation when the solid surface is bare or a smooth transiti on to a uniform him encircling the droplet. Both adsorbed and wetting films are considered, depending on the detailed behavior of the disjoining-press ure isotherm. (C) 1999 Elsevier Science B.V. All rights reserved.