Bridging effect from hexamethonium ions on carboxymethylcellulose solutions

Hexamethonium (HxM) is an unique divalent cation whose structure consists of two tetramethylammonium (TMA) connected by a hexyl bridge in the middle. Unlike alkaline earth metal ions, it is a) an organic ion that can interact with polymers and solvents non-ionically and b) has essentially two separated charge centres, rather than being a compact, singular charge. These properties may enhance the bridging effect in polyelectrolyte solutions; conversely, the length of the counterion may allow intrachain bridging.

Rheological and small-angle X-ray scattering (SAXS) measurements were carried to investigate the effect of hexamethonium ions on the structural and dynamic properties of carboxymethylcellulose solutions, and whether this polymer chain bridging is aided by the presence of this counterion.

Moreover, preliminary solubility tests in different solvents reveal that although HxMCMC has enhanced solubility compared to NaCMC, it is worse than TMACMC, which may be the result of some internal bridging. We have tentative viscosity data suggesting that unlike in the case of calcium, the viscosity-concentration scaling in the entangled regime is lower than that of NaCMC, possibly due to preferential intrachain bridging.