Micellesation vs aggregation in dilute solutions of amphiphilic heteropolymers

In recent experiments involving PNIPAM copolymers it has been observed that stable spherical nanoparticles are being formed by association of several chains in poor aqueous solution instead of aggregation. This type of mesosc opic structures called mesoglobules has an extremely monodispersed size dis tribution. Previously we have studied theoretically formation of clusters c onsisting of several chains in dilute solutions of amphiphilic heteropolyme rs. We have seen that the mesoglobules often possess an essentially micella r structure. In the current work we argue that formation of mesoglobules is strongly sequence and concentration dependent. In particular, by means of lattice Monte Carlo simulation we consider structures formed by a number of tri-block sequences and their certain mutations. For sequences consisting of two hydrophilic ends with a hydrophobic middle the size distribution of the resulting particles is rather narrow, i.e. mesoglobules are being forme d. However, in the case of sequences with two hydrophobic ends and a hydrop hilic middle a new type of structures seems to be prevalent. These consist of small mesoglobules interconnected by hydrophilic bridges. Clearly, on in creasing the concentration these networked structures would play an importa nt role resulting in a rapid onset of a gel-like behaviour. (C) 2001 Elsevi er Science BN. All rights reserved.