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The equilibrium structure of an interpolyelectrolyte complex (IPEC) coacervate consisting of weakly charged flexible polyanions and polycations with equal degree of ionization is considered. We study effects of salt concentration cs and solvent quality defined by second virial coefficient v on polymer density, surface tension, salt absorption, and correlations of charges and monomer units in equilibrium IPEC. Five different scaling regimes of IPEC are revealed, and a salt-solvent quality (cs-v) diagram of coacervate states is constructed. Boundaries between different regimes correspond to crossovers between low/high salt concentrations and poor/Θ-/good solvent conditions. Derived scaling laws for coacervate physical properties in each of regimes are in agreement with analysis based on the random phase approximation (RPA). This study summarizes and complements current theoretical comprehension of symmetrical IPEC of weakly charged polyions. [ABSTRACT FROM AUTHOR]

We develop a scaling model relating the friction forces between two polyelectrolyte brushes sliding over each other to the separation between grafted surfaces, number of monomers and charges per chain, grafting density of chains, and solvent quality. We demonstrate that the lateral force between brushes increases upon compression, but to a lesser extent than the normal force. The shear stress at larger separations is due to solvent slip layer friction. The thickness of this slip layer sharply decreases at distances on the order of undeformed brush thickness. The corresponding effective viscosity of the layer sharply increases from the solvent viscosity to a much higher value, but this increase is smaller than the jump of the normal force resulting in the drop of the friction coefficient. At stronger compression we predict the second sharp increase of the shear stress corresponding to interpenetration of the chains from the opposite brushes. In this regime the velocity-dependent friction coefficient between two partially interpenetrating polyelectrolyte brushes does not depend on the distance between substrates because both normal and shear forces are reciprocally proportional to the plate separation. Although lateral forces between polyelectrolyte brushes are larger than between bare surfaces, the enhancement of normal forces between opposing polyelectrolyte brushes with respect to normal forces between bare charged surfaces is much stronger resulting in lower friction coefficient. The model quantitatively demonstrates how polyelectrolyte brushes provide more effective lubrication than bare charged surfaces or neutral brushes. [ABSTRACT FROM AUTHOR]

The self-assembly of synthetic diblockcopolymers has been extensivelystudied experimentally and theoretically. In contrast, self-assemblyof polypeptide diblock copolymers has so far been mostly studied experimentally.We discovered that the theory developed for synthetic diblock copolymerdoes not fully explain the self-assembly of elastin-like polypeptidediblock copolymers, leading us to generalize the theory to make itapplicable for these polypeptides. We demonstrated that elastin-likepolypeptide diblocks self-assemble into weak micelles with dense coresand almost unstretched coronas, a state not previously observed forsynthetic diblock copolymers. Weak micelles form if the surface tensionat the core–corona interface is low compared to that expectedof a micelle with a dense core. The predictions of the theory of weakmicelles for the critical micelle temperature, hydrodynamic radius,and aggregation number of elastin-like polypeptide diblocks are inreasonable agreement with the experimentally measured values. Theunique and unprecedented control of amphiphilicity in these recombinantpeptide polymers reveals a new micellar state that has not been previouslyobserved in synthetic diblock copolymer systems. [ABSTRACT FROM AUTHOR]