Abstract

We consider the theoretical model of an amphiphilic macromolecule with a complexstructure of hydrophobic/hydrophilic monomer units. Each unit consists of a hydrophobicgroup (H) in the backbone and a side hydrophilic group (P). The units are able to orient inthe density gradient at the surface layer of a globule. First, we use the densityfunctional method to obtain the surface tension at a flat surface. We obtain that theeffect of orientation decreases the surface tension of an amphiphilic globule incomparison with the surface tension of a homopolymer globule of the same density.Therefore, the amphiphilic globule is more stable with respect to the transition toa coil conformation. Then, macromolecules with strong orientational ability ofamphiphilic units are considered. The free energy of spherical, bead-like, disc-like andtorus-like globules is analysed for flexible and rigid macromolecules. For verylong macromolecules in poor solvent, it is predicted that a disc-like globule forflexible chains should be formed. It is shown that the coil–globule transition inamphiphilic macromolecules is in most cases accompanied by a disintegration of theinitially formed globule into several ‘bead globules’. Upon further increase of theattraction of hydrophobic units, these beads merge with each other with theformation of a disc-like or torus-like globule, depending on the chain stiffness.

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