Momentum-dependent interfacial tension in polymer solutions

A model for the interface between a concentrated and a very dilute polymer solution is studied by Monte Carlo simulations at temperatures below the Theta temperature (in bad solvent conditions). The wave-number dependent interfacial tension gamma(q) is extracted from an analysis of the capillary wave amplitudes. It is shown that gamma(q) decreases monotonically with q(2), while no evidence is found for the predicted increase gamma(q) proportional to kq(2) with a positive bending rigidity k of the interface at large q. Consequences for the interpretations of simulations and experiments on interfacial widths are briefly discussed.