Ion pairing controls rheological properties of "processionary" polyelectrolyte hydrogelsElectronic supplementary information (ESI) available: GPC chromatogram and 1H NMR of POH, HRMS spectra before and after metathesis, frequency-dependent rheology. See DOI: 10.1039/c6sm02022d

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. Short chains of anion-terminated poly(cationic) polymers self assemble in processions. We vary cationic moieties and counterion, to tune rheological properties of the resulting hydrogels over 3 orders of magnitude.