Mesoscale morphology and dissociation equilibrium in pH-sensitive block copolymer gels

Molecular thermodynamic model of a mesoscopic diblock copolymer gel is extended to ionomer gels that contain weak polyelectrolyte chains. The dissociation equilibrium of polyelectrolyte is taken into account. Chain elasticity is described in the strong-stretching limit. The electrostatic interactions are treated using the approximation of local electroneutrality that leads to a local version of the Donnan rule. Studied in this work are weakly acidic ionomer gels in equilibrium with an external solution of varying pH and salinity. For gels of spherical, cylindrical, bicontinuous and lamellar morphologies, we predict swelling and dissociation equilibria and illustrate the effect of nanoscale morphology on the shift of dissociation equilibrium in the swollen gel. (c) 2007 Elsevier B.V. All rights reserved.