Phase equilibria and clustering in size-asymmetric primitive model electrolytes

The low-temperature phase coexistence of size-asymmetric primitive model el ectrolyte solutions has been investigated by means of Monte Carlo simulatio ns. A multidimensional parallel tempering method is employed and results ar e analyzed by means of histogram reweighting. Coexistence curves and critic al constants are determined as a function of size asymmetry, lambda = sigma (+)/sigma (-), from 0.05 to 1. It is found that the critical temperature a nd the critical density decrease as lambda decreases. These trends appear t o contradict available integral-equation theoretical predictions. For highl y asymmetric systems, we report the formation of large chain-like and ring- like structures. These clusters are much larger than those observed in symm etric electrolytes, and they are shown to give rise to considerable finite- size effects. (C) 2001 American Institute of Physics.