Pressure Dependence of the Contact Angle

Abstract

When a liquid and its vapor contact a smooth, homogeneous surface, Gibbsian thermodynamics indicates that the contact angle depends on the pressure at the three-phase line of an isothermal system. When a recently proposed adsorption isotherm for a solid-vapor interface is combined with the equilibrium conditions and the system is assumed to be in a cylinder where the liquid-vapor interface can be approximated as spherical, the contact-angle-pressure relation can be made explicit. It indicates that a range of contact angles can be observed on a smooth homogeneous surface by changing the pressure at the three-phase line, but it also indicates that the adsorption at the solid-liquid interface is negative, and leads to the prediction that the contact angle increases with pressure. The predicted dependence of the contact angle on pressure is investigated experimentally in a system that has an independent mechanism for determining when thermodynamic equilibrium is reached. The predictions are in agreement with the measurements. The results provide a possible explanation for contact angle hysteresis.

Thermo-responsive stick-slip behavior of advancing water contact angle on the surfaces of poly(N-isopropylacrylamide)-grafted polypropylene membranes

“…Wettability is one of the most important properties of a solid surface, which is often assessed by the contact angle (CA) of a liquid droplet placed on the surface [1][2][3][4][5]. CA is highly sensitive and can be affected by both surface chemistry and surface roughness.…”

Adsorption at the solid–liquid interface as the source of contact angle dependence on the curvature of the three-phase line

“…The system can come to equilibrium in the configuration shown in Fig. 2 [22,23,28,35]. We refer to this as the two-interface configuration.…”

“…Although the effect of n SL on the contact angle has been neglected, with few exceptions [20,22,29,31,35], a recent study found that n SL is negative [33]. Although a negative value of n SL is consistent with the Gibbs method of defining the position of the interface [8,21,25], the prediction that follows is that, independently of any line tension, for a given curvature of the three-phase line, the contact angle increases as the pressure in the liquid at the three-phase line, P 3 L , is increased [35], but that, for a given value of P 3 L , the contact angle decreases as C cl increases [32]. In other words, the contact angle does depend on the curvature of the three-phase line, not because of line tension, but because of adsorption at the solid-liquid interface.…”

Sessile drop evaporation on (super)hydrophobic surfaces: Effect of low pressure on the contact line dynamics

“…Previous experimental [27][28][29][30] and numerical [31,32] studies dealing with the pressure dependence of both the interfacial energies and the contact angle showed that an increase of pressure, at constant temperature, induces a decrease of the surface tension. The referred experiments require however the presence of a second component as an inert gas, which modifies the pressure sensitivity of the system [27].…”