Condensation phase transitions in bidisperse colloids

Condensation phase transitions in polydisperse colloids are studied theoretically. For maximal simplification of calculations, a bidisperse model of the system, consisting of relatively big and small particles, is considered. Direct van der Waals interactions between big particles as well as depletion forces between them due to small particles are taken into account. The diagrams of "gas-liquid", "gas-solid" and "liquid-solid" phase transitions in an ensemble of the big particles are constructed. The influence of size and concentration of small particles on the phase transitions is studied. Our results show that increase in concentration of small particles leads to increase in the initial temperature of the phase transition, i.e., the presence of small particles stimulates the separation of the colloidal system into two phases with different concentration of the big particles. On the other hand, concentration of big particles, needed for the phase transition, increases with the total concentration of small particles. This factor makes realization of this phenomenon more difficult. (C) 2004 Published by Elsevier B.V.