Chain molecules at high densities at interfaces

We have reviewed the general principles of interfacial constraint on highly concentrated polymers near sharp interfaces. First, chains are constrained by their inability to penetrate the boundary. Second, at high concentration, polymers are also constrained by interactions with neighboring chains. Third, one additional constraint depends on the chain length: (a) for long chains, a symmetry condition arises from the indistinguishability of segments k and k + 1, whereas (b) for shorter molecules, wherein the segments are distinguishable, the length of the chains is fixed. Subject to these restraints, chains at equilibrium will be configured to maximize their entropy, and hence their configurational disorder. The physical properties of chains at interfaces are often quite different from those of bulk polymers. In most such systems, the conformational ordering is dissipated within only 5-10 A from the interface, but some physical properties depend on effects that are propagated over much longer distances. The currently available theory is found to be in quite good general agreement with a large number of conformational and mixing properties of polymers at interfaces, in semicrystalline polymers, in alkane crystals, in stationary phases used in reversed-phase liquid chromatography, and in amphiphilic aggregates including bilayer membranes and micelles.