We present a systematic numerical study of the phase behavior of square-well fluids with a ''patchy'' short-ranged attraction. In particular, we study the effect of the size and number of attractive patches on the fluid-fluid coexistence. The model that we use is a generalization of the hard sphere square well model. The systems that we study have a stronger tendency to form gels than the isotropic square-well system. For this reason, we had to combine Gibbs ensemble simulations of the fluidfluid coexistence with a parallel tempering scheme. For moderate directionality, changes of the critical density and the width of coexistence curves are small. For strong directionality, however, we find clear deviations from the extended law of corresponding states: in contrast to isotropic attractions, the critical point is not characterized by a universal value of the reduced second virial coefficient. Furthermore, as the directionality increases, multiparticle bonding affects the critical temperature. We discuss implications for the phase behavior, and possibly crystallization, of globular proteins.
The two-dimensional viscous froth model is a simple tractable model for foam rheology and coarsening. It includes, but is not confined to, the quasistatic regime. Here we present a detailed analysis and implementation of the model, illustrated with various examples. With certain simplifying assumptions, it provides significant insight into strain-rate-dependent effects in foam rheology and elsewhere, particularly in relation to recent experiments.
Europhysics Letter was launched more than fifteen years ago by the European Physical Society, the Société Française de Physique, the Società Italiana di Fisica and the Institute of Physics (UK) and owned now by 17 National Physical Societies/Institutes. Europhysics Letters aims to publish short papers containing non-trivial new results, ideas, concepts, experimental methods, theoretical treatments, etc. which are of broad interest and importance to one or several sections of the physics community. Europhysics letters provides a platform for scientists from all over the world to offer their results to an international readership.
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