Globules of amphiphilic macromolecules

Abstract

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

Non-ionic Thermoresponsive Polymers in Water

“…Also, the possibility that electrostatic effects contribute to the stabilization of PiPAAm mesoglobules cannot be excluded [55,193]. Since our previous review [55], some new fascinating and important evidence has appeared, including experimental [54,[194][195][196][197][198][199][200][201][202][203] and theoretical [204][205][206] aspects of the mesoglobular phase.…”

Microstructuring of a polymer globule in solution in the presence of an amphiphilic substance

“…In general, the shape of the curves of the transition to a microstructured state is convex. In expression for free energy (21), the terms depending on the orientation ability of the surfactant molecules contain product , where the values of depend on volume fraction of the surfactant in the solution,…”

“…For this macromolecule, the possibility of formation of both a disklike globule and a globule in the form of a sequence of beads has been previously predicted in computer simulations [20] and theoretically [21]. The surface tension coefficient of the globule decreases owing to the orientation of amphiphilic units on the surface and the difference in the interaction energies of the parts of the unit with their environment, and the spherical shape of the globule ceases to be the most favorable.…”

“…(22)-(24) for fluctuation into the expression for respective free energy variation (21), we can write the bulk density of free energy vari ation Δf = ΔF/V, which corresponds to the discussed microstructure type, as follows:…”

“…Through generalization of the mean field theory methods developed in [21] to take into account the effect of the orientation of bonds that link together the hydrophobic and polar parts of the amphiphilic unit, in [22], we calculated the surface tension and the change in the coil-globule transition temperature for a homopolymer macromolecule in a surfactant solution and determined the size of the globule and the selective sorption of the surfactant as a function of its concentration and the degree of amphiphilicity of the molecules. In addition, it was predicted that microstructuring in the bulk of the globule can occur in the case of a fairly large difference in interaction energies of polymer units and parts of the surfactant.…”