Configurational state of adsorbed chain molecules. Behaviour of terminally anchored chains

Abstract

The configurational behaviour of an isolated terminally “anchored” chain molecule interacting with a surface has been investigated using a computational statistical technique. The technique involves the simulation of the canonical ensemble of the system by a method analogous to that of Metropolis et al. The present study assumes a lattice model with a square-well potential function for the segment/segment and segment/surface interactions. The solvent effect is incorporated in the model through the segment/segment interactions: it is assumed that good solvents produce repulsions between the segments, while bad solvents lead to attraction. The bonds in the chain assume three conformational states, viz. trans, gauche⁺ and gauche^–, with the trans/gauche conformational energy difference equal to 1 kT. It was found that in a good solvent the molecule exists in an extended state. The outstanding feature of the configuration is long “tail” protruding into the solution phase, and there is a lower tendency for the formation of “loops”. A bad solvent, on the other hand, renders the molecule coiled and promotes the formation of “loops”.