Collapsed States of a Macromolecule Interacting with an Amphiphilic Substance

摘要

We analyze in theory the conformations of macromolecules in a poor solvent focusing on the structure of collapsed states formed in the presence of an amphiphilic substance. Strongly amphiphilic molecules are described as dimers with hydrophobic and hydrophilic parts that can be similar to asymmetric liquid crystals or surfactant molecules. The hydrophobic parts of dimer molecules at the globule surface are embedded in the globule, leading to a decrease in the surface free energy and thus facilitating the formation of nonspherical shapes. For very long macromolecules, we predict the formation of only a spherical globule or a necklace-like structure (beads). For shorter macromolecules, an intermediate rodlike structure can be formed as well. The morphology diagrams are presented in the coordinates of the amphiphilic substance volume fraction in solution and the amphiphilicity parameter of dimer molecules. All transitions between the structure types upon a temperature change (related to a change in the amphiphilicity parameter) are of the first order. The polymer density in a collapsed state can be considerably larger in the presence of an amphiphilic substance than without it. The region of stability of spherical globules widens with an increase in the solvent quality or in the volume of the polar part of a dimer molecule and with a decrease in its length.