Adsorption of chain molecules into a thin film structure and solvation interaction versus molecular flexibility

The influence of molecular flexibility on the properties of thin fluid film s formed by linear chain molecules is studied by means of a singlet level o f inhomogeneous integral equation theory. The considered m-mer chain molecu les are formed through the polymerization of m hard-sphere beads with two s ticky bonds randomly placed inside each bead core. Different molecular flex ibility, from totally flexible up to almost completely rigid is reached by varying the interbead bonding length. The homogeneous properties of the sam e model that is necessary input to the singlet approach are extracted from the Wertheim's theory of polymerization. The adsorption, local density dist ribution, disjoining pressure and solvation force of the chain molecule fil ms confined by attractive and repulsive surfaces are analyzed. The obtained results indicate significant influence of the molecular flexibility on the film layering that is the origin of oscillations of solvation interaction arising between film surfaces. The oscillations of solvation pressure and f orce become more pronounced with restriction of molecular flexibility and w ith increase of bulk volume fraction of chain molecules. The decay of the o scillations across the film depends on the chain length and on the physical nature of the film surfaces, i.e. whether they are lyophilic or :lyophobic . The partitioning of chain molecules from the bulk into the film strongly depends on the chain flexibility and this effect is more pronounced for the lyophilic surfaces. (C) 2000 Elsevier Science B.V. All rights reserved.