Lattice model simulation of adsorption of linear, multisegmented molecules onto CaF2 out of organic solvents. I. Adsorption ofn-alkyl alcohols out ofn-hexane andn-dodecane

Abstract

Theoretical adsorption curves have been calculated using a lattice model for the adsorption of linear, multisegmented molecules. The results have been compared with the experimental data of n-alkyl alcohols adsorbing out of hexane and dodecane onto CaF 2 . Good agreement or good consistency between experiment and theory is achieved by using energies of interaction determined a priori when each methyl, methylene, and hydroxyl group is assigned one segment. The segment-to-segment interaction energies are obtained using a group interaction (lattice) model which adjusts them to get the best simulation of the bulk thermodynamic data of the pure components and their binary mixtures. The segment-to-segment interaction energies at the surface are assumed to be the same as they are in the bulk. The methyl- and methylene-surface interaction energies are assumed to be negligible compared to the hydroxyl-surface interaction energy (XA); hence, the only adjustable parameter is XA. The experimental adsorption curves are simulated using computer programs for the dimer (AB), trimer (ABB), tetramer (ABBB), and hexamer (ABBBBB) in a solvent monomer, C, wherein the A segment is a hydroxyl group, the B segment is a methyl or methylene group, and the C segment is one of the methyl or methylene groups comprising the n-alkane solvent. The optimum values for XA are calculated to be −4.77 in hexane and −5.53 in dodecane with units of kilocalories per mole of hydroxyl contacts with the CaF 2 surface. In addition, a solvent chain length effect has been inferred from the lattice model analysis of the experimental data.