Polyelectrolyte hydrogel thickeners can be classified as rheological modifiers. They are used extensively in pharmaceutical and cosmetic applications without detailed knowledge of the microstructure and microviscosity. As these two properties relate heavily to their rheological and absorption behaviors, it is essential to gain a greater understanding. Crosslinked polymer hydrogels often exhibit wall slippage when using conventional rheometry, leading to an underestimation of rheological properties. Therefore, a more accurate form of characterization is needed. The use of a unicellular, flagellated protist, <i>Euglena</i>, as a probe provides a facile method to simultaneously examine the microviscosity and microstructure of these hydrogel systems. The heavily crosslinked nature and “fuzzball” structure of Polycarbophil, Carbomer, and Sodium Acrylate Crosspolymer hydrogels likely makes it impossible to define their concentration regimes using previously established regimes for polymers in solution. Through the use of optical microscopy, the <i>Euglena</i>’s ability to traverse through the hydrogel is used to characterize and define both the concentration regimes and critical transitions in the system. This method was effective in estimating the dilute and semi-dilute regimes, along with the critical overlap concentration, C*, defined as the transition between these two regimes. Further testing must be done to determine the existence of a concentrated regime, and whether any such regime is due to polymer chain entanglement or a closely packed system.

Probing the microstructure: Determination of the concentration regimes of polyelectrolyte thickeners via the immersion of microorganisms

ACS Spring Meeting 2021

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