Analysis of stability of macromolecular clusters in dilute heteropolymer solutions

We study the formation of clusters consisting of several chains in dilute s olutions of amphiphilic heteropolymers. By means of the Gaussian variationa l theory we show that in a region of the phase diagram within the conventio nal two-phase coexistence region mesoglobules of equal size possess the low est free energy. Monte Carlo simulation confirms that the mesoglobules are stabilized due to microphase separation, which introduces a preferred lengt h scale. The very existence of such mesoscopic structures is related to a d elicate balance of the energetic and entropic terms under the connectivity constraints. The issue of size monodispersity and fluctuations for mesoglob ules is investigated. (C) 2000 American Institute of Physics. [S0021-9606(0 0)51018-6].