A MEAN-FIELD DESCRIPTION OF POLYELECTROLYTE MESOGELS

Microphase separation in ABA triblock copolymers creates microdomains of A blocks that are physically cross-linked to each other by B blocks: the so-called mesogel microstructure. The B blocks can adopt two basic conformations: they can be tethered to two A domains (bridges) or to only one A domain (loops). In this study the lamellar morphology of these mesogels is considered. The B block is considered to be a polyelectrolyte with a backbone that can be hydrophobic. Swelling of such gels in aqueous media is theoretically explored-specifically two limits are explored (i) the salt dominance limit and (ii) the no salt limit. Equilibrium swelling characteristics of these gels as well as the response to external pressure, in the swollen state, are predicted. In the high salt concentration regime a continuous transition from the collapsed to swollen state is observed for changes in the backbone solvancy. The collapse transition is unaffected, in the salt dominance limit, by the fraction of loops or bridges. The elongation in salt dominance strongly depends upon the loop fraction, but the compression is independent of the loop fractions. A strong contrast is seen in the no salt limit case where the collapse transition is discontinuous with changing excluded volume (or charge fraction) and hysteresis can be observed. The collapse transition is now affected by the loop fraction-indeed critical behavior is observed with changing loop fraction. The elongation and compression are both affected by the loop fraction in the no salt limit.