Study of mesoglobules in solutions of amphiphilic heteropolymers

Abstract

We study the conformational states in solutions of amphiphilic copolymers by means of the Gaussian variational theory and lattice Monte Carlo simulation. We find that due to a delicate balance of microphase separation and entropic effects under the connectivity constraints macromolecular clusters consisting of a few distinct chains may become thermodynamically stable in some narrow regions of the phase diagram within the conventional two-phase coexistence region. These are characterised by a relatively monodispersed size distribution, with the mean size of these mesoscopic globules related to a characteristic scale of the microphase separation. Thus, in contrast to the homopolymer case, here collapse and aggregation can compete with each other, producing thermodynamically stable particles with a predominantly hydrophobic core and a hydrophilic shell. These were recently observed experimentally as, at least, rather long lived final states in the kinetics after quenching beyond the spinodal in aqueous solutions of poly(N-isopropylacrylamide) with some of the monomers hydrophobically modified.