Universality in the dependence of the drop contact angle on liquid-solid interactions and temperature obtained by the density functional theory

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A nonlocal density functional theory is employed to calculate the contact angles of nano- and macrodrops on smooth solid surfaces in wide ranges of temperature and parameters of the Lennard-Jones potentials representing the fluid-fluid and fluid-solid interactions. For both types of drops, simple linear dependencies of the contact angle on the fluid-solid energy parameter ∊ fs was found for various temperatures and hard core fluid-solid parameters σ fs . Expressions are suggested that relate the contact angle θ to the parameters of the interaction potentials and temperature. The most intriguing feature was that for each considered σ fs there is a value ∊ 0 of ∊ fs for which the contact angle θ = θ 0 becomes independent of temperature and of σ fs . It is shown that ∊ fs = ∊ 0 divides the materials for which θ increases from those for which θ decreases with increasing temperature.