Solvation force between surfaces modified by tethered chains: A densityfunctional approach

摘要

The behavior of Lennard-Jones fluid in slitlike pores with walls modified by tethered chainmolecules is studied using density functional theory. The effects of confinement and chemicalmodification of pore walls on the solvation force are investigated. Two models of the pore walls are considered. According to the first model, the chain molecules are chemically bonded by their endsegments to opposite walls of the pore, forming flexible pillars. In the second model the chains build up a brush at each wall due to bonding of the first segment at one wall. The nonbonded terminating segment of a molecule is strongly attracted via a short-range potential to any wall of the pore. Thena pillarlike or looplike structure of chains can be formed. In the first model the solvation force at the wall-to-wall is repulsive for narrow pores and strongly attractive for wider pores of the order of thenominal chain length. Oscillations of the solvation force are induced by adsorbed fluid structure and by ordered structure of segments on the fragment of entirely attractive force curve. In the secondmodel, however, the solvation force decays to zero as the pore width increases. Attractive force can be induced at intermediate separation between walls due to modification of the pore walls.