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Lattice Monte Carlo simulations describe the adsorption of protein-like heteropolymer chains at an oil/water interface. The heteropolymers are designed sequences of 27 and 64 amino acid-type lattice sites taken from a 20-letter alphabet. We use our recently suggested energy scale to model oil and water. We investigate the effect of the oil parameters on adsorption properties of a single chain and on the aggregation of adsorbed chains while keeping the water parameters fixed to their optimum values found previously. By varying the oil parameters, we can cause a large range of adsorption behavior: from no adsorption to reversible adsorption to irreversible adsorption. We compare adsorption at a liquid/ solid interface to that at a liquid/liquid interface. A liquid interface leads to stronger adsorption and denaturation than a solid interface with the same water and oil interaction parameters. We propose "optimal" oil parameters and use them to study multichain adsorption at a liquid interface.

Lattice Monte Carlo simulations have been employed to calculate depletion interaction of excluded volume chains in a weakly attractive slit, particularly in the region around the critical point of adsorption. The simulations were performed under full equilibrium conditions where a dilute solution in a slit was in contact with the reservoir. The free energy of confinement deltaA, the force f, and the relative pressurepI/pE on the slit walls were calculated as a function of slit width D and the attraction strength epsilon. The depletion region in the pressure profile pI/pE vs D is reduced by an increase in the attraction potential epsilon in a manner resembling the influence of polymer concentration. At the critical point of adsorption epsilonc the depletion interaction vanishes both in the pressure pI/pE and in the intraslit concentration profile phiI(x). The parameters used to assess the stability of colloidal dispersions such as the depletion potential W(D) (an integral of the net pressure deltap) reach a unique value at the critical condition. A monotonic repulsive profilepI vs D was found for chains trapped in the slit at restricted equilibrium. The mean dimensions (R2) of chains compressed in attractive slits feature a distinct minimum at intermediate slit widths.

The adsorption of a metal monolayer or submonolayer for the systems Ag/Au(100), Au/Ag(100), Ag/Pt(100), PUAg(100), Au/Pt(100), Pt/Au(100), Au/Pd(100), and Pd/Au(100) was studied by means of lattice Monte Carlo simulations. It was found that, taking into account some general trends, such systems can be classified into two big groups. The first one comprises Ag/Au(100), Ag/Pt(100), Au/Pt(100), and Au/Pd(100), which have favorable binding energies as compared with the homoepitaxial growth of adsorbate-type atoms. When the simulations are performed in the presence of substrate-type islands in order to emulate surface defects, the islands remain almost unchanged, and the adsorbate atoms successively occupy kink sites, step sites, and the complete monolayer. The second group is composed ofAu/Ag(100), Pt/Ag(100), Pt/Au(100), and Pd/Au(100), for which monolayer adsorption is more favorable on substrates of the same nature than on the considered substrates. When simulations are carried out in the presence of islands of substrate-type atoms, these tend to disintegrate in order to form 2D alloys with adsorbate atoms.

Three-dimensional lattice-based Monte Carlo simulations of mixed amphiphile systems are investigated, and the simulated critical micelle concentrations (cmc's) are compared with the predictions of both a molecular thermodynamic theory and a regular solution theory. The head−head interactions between identical surfactant species are varied to mimic nonideal mixing and to manipulate the net attraction (or repulsion) between surfactant species. The simulations indicate that the head−head interaction affects not only the cmc but also aggregate size and structure. The simulated cmc as a function of overall surfactant composition is in reasonable agreement with the theoretical models when a fitted value for the interaction parameter, β, is used. The fitted value is in good agreement with a value estimated a priori from the lattice model for the surfactants with attractive headgroups, but there are large discrepancies for the case of repulsive headgroups. The discrepancies in the latter are caused by nonrandom m...