COMBINATORIAL ENTROPY AND THE STATISTICAL-MECHANICS OF POLYDISPERSITY

A new method to treat statistical mechanics in a polydisperse system i s described, applicable when the nonideal part of the free energy depe nds only on a few moments of a size distribution. A simple entropic co ntribution to the free energy is identified from combinatorial conside rations. Although approximate in the general case, the method obtains the exact spinodal curve, critical points, cloud curve, and shadow cur ve. Polydisperse Flory-Huggins theory is treated as an example.