  Over the past decade or two, the concept has emerged of using multiple types
of weak interactions simultaneously to enhance the mechanical properties of
elastomers. These weak interactions include physical entanglements, hydrogen
bonds, metal-coordination bonds, dynamic covalent bonds, and ionic bonds. The
combination of entanglements and ionic bonding has been minimally explored and
is particularly exciting because of the broad application space for
polyelectrolytes. In this work, a constitutive model framework is developed to
describe the response of elastomers with both ionic bonds and entanglements. We
formulate a micromechanical model that couples together chain stretching, ionic
bond slipping, and entanglement evolution. The ionic bonds provide toughness by
enabling plastic deformation in comparison to covalently crosslinked material
and add strength compared to a linear polymer. Evolution of the entanglement
density is taken as a key mechanism that can govern stiffness, toughness, and
self-recovery in elastomers. The model is used to match bulk polyelectrolytes
with different fractions of ionic components under a variety of loading
histories. The variations in material parameters are then used to help
understand the relative importance of different governing mechanisms in the
bulk polymers. We show that the theoretical framework can explain our
experimental uniaxial tensile experimental results for polyelectrolytes. This
model can help to design better material with high stiffness and toughness. We
expect that our model can be extended to explain the mechanical behavior of
other polyelectrolytes and other soft materials with a wide range of dynamic
bonds.
