Lattice model simulation of adsorption of linear, multisegmented molecules onto CaF2 out of organic solvents II. Adsorption ofn-alkyl amines out ofn-hexane,n-dodecane, cyclohexane, adn benzene, and alkyl diamines out of benzene

Abstract

Abstract The results of theoretical calculations using a lattice model for the adsorption of linear, multi-segmented molecules are compared with the experimental data ofn-alkyl aminse adsorbing out of hexane, dodecane, cyclohexane, and benzene onto CaF2, as well as the alkyl diamines adsorbing out of benzene onto CaF2. Good agreement or good consistency between experiment and theory is achieved using energies of interaction determined a priori when each methyl, methylene, and amine group is assigned one segment. The segment-to-segment interaction energies are obtained using a group interaction (lattice) model, as in Part I of this series. The experimental adsorption curves are simulated using the computer programs described in Part I, as well as a program for the symmetrical tetramer (ABBA/C). Whne a one-site model is assumed, the segment-to-segment interaction energies are the same at the surface as they are in the bulk of the solution, with the exception of the amine-amine interaction energy, which must then be smaller in magnitude at the surface. Hence, the five adjustable parameters are: the adsorption strength of group out of solvents with 6 or 12 carbon atoms per molecule (XA) and the adsorption strength of the benzene with the CaF2 surface (XCφ; the amine-aromatic carbon interaction energy parameter. φij (which determines EAC, where EAC = EAC1); and the amine-amine interaction energy at the surface (EAA1). When a two-site (patchwise heterogeneity) model is postulated, six adjustable parameters are required; however, all the segment-to-segment interaction energies-including the amine-amine interaction energy—are the same at the surface as they are in the bulk of the solution. As in Part I, from the lattice model analysis of the experimental data, we infer a solvent chain length effect on the adsorption.