Surface tension and contact angle of a liquid–solid interface

Abstract

The contact angle between a liquid film and a solid substrate is treated in the van der Waals model used previously by the author to discuss gas adsorption on solid surfaces. The model accounts for the occurrence of three types of wetting behavior, i.e., complete wetting, partial wetting, and nonwetting, as well as for transitions between these different regimes. According to this model, the contact angle depends on two parameters, namely the reduced temperature T/Tc, where Tc is the critical temperature of the liquid, and εw/kTc, where εw is the minimum in the liquid–solid interaction potential. For high-energy surfaces, corresponding to large εw/kTc, the contact angle decreases on increasing temperature; the opposite behavior is predicted to occur on sufficiently low-energy surfaces. With some hypotheses on how εw depends on the nature of the solid and liquid phases present, one can calculate the variation in contact angle with liquid species for a given solid at fixed temperature. The theory is compared with contact-angle results for n-alkanes on teflon surfaces; qualitative agreement is found. The contrasts between the present model and previous theories for the contact angle, in particular those of Good and Girafalco, Navascués and Berry, and Cahn, are discussed. Whereas Cahn predicts that the transition between different wetting classes is first-order in nature, we find that it is actually of second order.

Pool Boiling Performance Comparison of Smooth and Sintered Copper Surfaces with and Without Carbon Nanotubes

“…Values of  must be assumed, since no information is available in the literature for contact angles on CNT 18 walls at elevated temperature. Based upon the work of Wang et al [42] and Sullivan [43], we estimate the contact angles to be, to first order, 20° and 120° for HFE-7300 and DI water, respectively, at the saturation temperature.…”

Density-functional theory of the crystallization of hard polymeric chains

“…For the description of the melt phase they used a polymer reference interaction site model or PRISM, [10][11][12] whilst the crystal phase was described in a local-density type of approximation. 13,14 The agreement of the theory with experimental data on the densities at which the polymers polyethylene and polytetrafluoroethylene crys-tallize was quite remarkable. Somewhat less good was the predicted phase gap, which was overestimated by a factor of about 3, as well the temperature dependence of the density.…”

Wetting and drying scenarios of ionic solutions

“…Following the pioneering work of Cahn [18], phenomenological theories are based on generalisations of van der Waals classic "square gradient" theory of the liquid/vapour interface [12,23,24]. Microscopic theories, starting from a molecular description of the fluid, were pioneered by Ebner and Saam [19], and by Sullivan [25,26], and culminated in the decisive work of Evans and collaborators [21,[27][28][29]. Following van der Waals, Cahn assumes the density profile ρ(z) to vary slowly near contact.…”

“…Microscopic density functional theories are based on a molecular model of the fluid, which specifies the Hamiltonian of the system, i. e. the interactions between the molecules [19,21,[25][26][27][28][29]. Following van der Waals, the pair potential is split into a short-range repulsion and long-range (LR) contributions (dispersion and Coulombic interactions).…”

“…Following the work of Sullivan [25,26] and of Evans and coworkers [21,[27][28][29], Yukawa-like attractions between all species are assumed. The pair potentials are hence chosen of the generic form (α, β = 0, +, −):…”