Monte Carlo simulations of the adsorption of amphiphilic oligomers at hydrophobic interfaces

The adsorption of amphiphilic oligomers from solution to different interfaces has been studied using a lattice model. The oligomers consist of one hydrophobic and one hydrophilic block and can form micellar aggregates in solution at sufficiently high concentrations. We have investigated the relationships among the amphiphile bulk concentration, its chemical potential, and adsorbed amount. Below the critical micellization concentration (cmc) the amphiphile chemical potential is a logarithmic function of the concentration, above the cmc it becomes constant. When the amphiphile solution is in contact with a hydrophobic surface, the hydrophobic blocks adsorb to the surface and the hydrophilic blocks protrude into the solution. As the adsorbed amount increases, the adsorbed molecules become laterally more confined and stretch away from the interface. The adsorption isotherm shows a plateau at high bulk concentration, which is due to the constant chemical potential above the cmc. The influence on the adsorption of both the interaction between the amphiphile and the solvent, and between the amphiphile and the interface are investigated. Finally, the adsorption at a hard hydrophobic surface is compared with the adsorption at a fluid interface.