Ion pairing controls rheological properties of "processionary"   polyelectrolyte hydrogels
  We demonstrated recently that polyelectrolytes with cationic moieties along the chain and a single anionic head are able to form physical hydrogels due to the reversible nature of the head-to-body ionic bond. Here we generate a variety of such polyelectrolytes with various cationic moieties and counterion combinations starting from a common polymeric platform. We show that the rheological properties (shear modulus, critical strain) of the final hydrogels can be modulated over three orders of magnitude depending on the cation/anion pair. Our data fit remarkably well within a scaling model involving a supramolecular head-to-tail single file between cross-links, akin to the behaviour of pine-processionary caterpillar. This model allows the quantitative measure of the amount of counterion condensation from standard rheology procedure. 
Hassan Srour, Martien Duvall Deffo Ayagou, Thi Thanh-Tam Nguyen,   Nicolas Taberlet, S\'ebastien Manneville, Chantal Andraud...
cond-mat.soft cond-mat.mtrl-sci