Prediction of the wetting condition from the Zeta adsorption isotherm

Abstract

We use the Zeta adsorption isotherm and propose a method for determining the conditions at which an adsorbed vapour becomes an adsorbed liquid. This isotherm does not have a singularity when vapour phase pressure, P(V), is equal to the saturation-vapour pressure, Ps, and is empirically supported by earlier studies for P(V) < Ps. We illustrate the method using water and three hydrocarbon vapours adsorbing on silica. When the Zeta isotherm is combined with Gibbsian thermodynamics, an expression for γ(SV), the surface tension of the solid-vapour interface as a function of x(V)(≡P(V)/Ps) is obtained, and it is predicted that adsorption lowers γ(SV) from the surface tension of the substrate in the absence of adsorption, γ(S0), to that at the wetting condition. The wetting hypothesis indicates that γ(SV) at wetting, x, is equal γ(LV), the surface tension of the liquid-vapour interface. For water vapour adsorbing on silica, adsorption lowers γ(SV) to γ(LV) at xVW equal unity, but for the hydrocarbons heptane, octane and toluene adsorbing on silica xVW is found to be 1.40, 1.30 and 1.32 respectively.

Nucleation and growth of condensate in nanoporous materials

“…Historically, y has been assumed to be independent of the pressure in the liquid at the three-phase line, 17 but this assumption is not supported by recent experiments. 10,[18][19][20][21][22] Adsorption at this interface is indicated to increase the contact angle as the pressure is increased.…”

Modeling of type IV and V sigmoidal adsorption isotherms

“…The isotherm can display a sigmoidal course for z 4 1. 41 A general multilayer isotherm, which maps also the course of type IV and V, has been published by Brunauer et al 42 after their pioneering work in 1938 39 as an extension of the BET equation by assuming that increasing the number of multilayers n is coupled with an enhanced probability to be adsorbed on both sides of the capillary walls. The following equation, also known as BDDT isotherm, has been derived:…”

Synthesis and Characterization of Modified Sepiolite for the Adsorptive Removal of Rhodamine B from Wastewater

“…1/n<1 also showed the adsorption process is chemical adsorption in Table 6. The correlation coefficients R 1 2 was positively correlated to n(when the n<1, R 1 2 nearly equal to 1) which also indicated adsorption is a monolayer adsorption [24][25][26][27].…”