Rheological and dielectric behavior of sodium carboxymethyl cellulose (NaCMC)/Ca²⁺ and esterified NaCMC/Ca²⁺...

Polyelectrolyte-based conductive hydrogels are being extensively explored for applications in energy storage and as electrode materials for batteries. We synthesized ionically crosslinked sodium carboxymethyl cellulose (NaCMC), esterified NaCMC, and Ca²⁺ doped esterified NaCMC hydrogels. This work aims to understand the effect of Ca²⁺ ions on the NaCMC and esterified NaCMC. FTIR, SEM, Rheology and EIS studies were performed to understand the structure and dynamics of hydrogels. Results confirmed that Ca²⁺ ions have an important role in determining the rheological and dielectric response of hydrogels. Power law behavior was observed in their rheological response with exponent (n) of 0.81 for G' and 0.76 for G″ of ionically crosslinked NaCMC, 5.38 for G' and 4.70 for G″ of esterified NaCMC, whereas, negative exponents -1.44 for G' and -1.10 for G″ of Ca²⁺ ion doped esterified NaCMC. Ionically crosslinked NaCMC hydrogels have relaxation times (τ) in the range of 8.9 × 10^-5 s-2.8 × 10^-5 s may be due to the formation of temporary dipoles by electrostatic bridge formations with dc conductivity of (0.1 S/cm-5 S/cm), whereas, esterified NaCMC showed relaxation times (10^-3 s-8.9 × 10^-5 s) with increasing ester crosslinks and dc conductivity of (0.05 S/cm-0.8 S/cm). Interestingly, Ca²⁺ ion doped esterified hydrogels showed multiple dielectric relaxations on Ca²⁺ ion addition with different relaxation times may be due to change in ionic environment. The understanding obtained from this work may be useful for designing tuneable hydrogels with optimum electrical and mechanical properties.