Binding potential and wetting behavior of binary liquid mixtures on surfaces

Abstract

We present a theory for the interfacial wetting phase behavior of binary liquid mixtures on rigid solid substrates, applicable to both miscible and immiscible mixtures. In particular, we calculate the binding potential as a function of the adsorptions, i.e., the excess amounts of each of the two liquids at the substrate. The binding potential fully describes the corresponding interfacial thermodynamics. Our approach is based on classical density functional theory. Binary liquid mixtures can exhibit complex bulk phase behavior, including both liquid-liquid and vapor-liquid phase separation, depending on the nature of the interactions among all the particles of the two different liquids, the temperature, and the chemical potentials. Here we show that the interplay between the bulk phase behavior of the mixture and the properties of the interactions with the substrate gives rise to a wide variety of interfacial phase behaviors, including mixing and demixing situations. We find situations where the final state is a coexistence of up to three different phases. We determine how the liquid density profiles close to the substrate change as the interaction parameters are varied and how these determine the form of the binding potential, which in certain cases can be a multivalued function of the adsorptions. We also present profiles for sessile droplets of both miscible and immiscible binary liquids. Published by the American Physical Society 2024

Experimental and theoretical bulk phase diagram and interfacial tension of ouzo

“…This feature is discussed further below. With much trial and error and also drawing experience from previous work 18,21,30,31,37,48 we find the following values give surprisingly good agreement with the experimental phase diagram: βε ww = 0.96, βε wa = 0.84, βε aa = 0.78, βε ao = 0.63, βε oo = 0.78, βε wo = 0.30.…”

“…The behaviour of liquids in contact with surfaces is a particularly important aspect worth investigating, due to its every-day relevance. As mentioned in the introduction, lattice DFTs of the type used here have already been used successfully in studies of the wetting behaviour of one-component liquids on surfaces 18,21,22 adsorption studies, 23–25 binary liquid mixtures on surfaces, 26–32 and various other applications. 33–36 The work presented here now paves the way e.g.…”

“…30,37,47 In other words, when we use the model to calculate the shape of liquid droplets on surfaces, the droplet interfaces are almost perfectly hemispherical, as expected. 31,36…”

“…The lattice DFT that we use may be viewed as being based on classical DFT for continuum fluids 19,20 and as being a coarse-grained (discretized) approximation to a continuum DFT. Lattice DFT has been used to describe one-component liquids on surfaces, 21,22 adsorption in porous media, 23–25 binary liquid mixtures on surfaces, 26–32 colloid aggregation behaviour 33–35 and to determine the stability of nanoparticle laden aerosol droplets. 36 Here, we extend the model to describe ternary mixtures, with the interaction parameters chosen carefully to mimic the ouzo system.…”

“…ref. 31) and also in non-equilibrium studies by using the free energy we develop here together with dynamical DFT. 20,37,38…”