Lattice model of water iBA mixtures

To gain an understanding of the experimental findings, we adopt a lattice model of a binary fluid mixture similar to the one introduced in Section 4.6.1. As in Section 4.6.1, we consider a simple cubic lattice with lattice constant t. However, unlike in Section 4.6.1, we now assume molecules to occupy the cubic cells of volume formed by the surrounrUng lattice ates rather than occupying the sites thems es. This approach allows us to account for the different sizes of water and iBA molecules (see below). 

Each cell may be occ ipied by either D2O (W) or iBA (A), or it may be empty. The attractive interactions between the molecules are accounted for by a square-well potential where the width of the attractive well is f as before, which is to say that only molecules located in nearest-nei bor cells on the lattice interact directly with each other. The depths of the attractive wells are eww, WA and aa for water water, water iBA, and iBA iBA interactions, respectively. Because iBA molecules are about five times larger than water 

In the model of the pore, the mixture is confined between two planar, homogenous substrates perpendicular to the z-axis. Thus the two substrates are at 2 = 0 and z = 2 + 1, where z is the munber of lattice layers of the mixture parallel with the x-y plane. The width of the slit-pore is z . Molecules do not occupy lattice cells at = 0 and 2 = 2 + 1, which reflects the hard-core repulsion of the substrates. In the experimental system the water molecules are favored b - the pore wall. This preferential interaction with the substrate is modeled by a potential [107] 

E)quilibrium states of the water-iBA model mixture are characterized ly minima of the grand-potential density 

On the other hand, the incremental chemical potential in Exj. (4.146) defined 

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