The role of particle size and shape in highly size-asymmetric mixtures

It has long been known that entropy alone can be powerful enough to drive a phase transition. A binary mixture of differently sized hard spheres can exhibit many complicated crystalline phases. At large size ratios the small particles can essentially be used to tune the interaction between large particles. This is exploited to great effect in the control of colloidal dispersions and in some cases can drive fluid-fluid separation. Numerically, large size ratios are very difficult to deal with due to the small particles effectively jamming in the larger ones. Through the application of specialised Monte Carlo algorithms we have been able to circumvent the principal bottle neck allowing us to calculate effective potentials and even full phase behaviour for a range of model systems. The same techniques have also allowed us to explore the effect of particle shape. In particular I will show preliminary results for a lock-and-key system that is a model for protein binding that exhibits depletion driven self assembly.