Concentration-Dependent Ionic and Macromolecular Reorganization in Sodium Carboxymethyl Cellulose/Curcumin Systems

Sodium carboxymethyl cellulose (NaCMC) is a water-soluble anionic polyelectrolyte whose macromolecular organization is highly sensitive to solvent composition, ionic environment, and interactions with low-molecular-weight compounds. In this study, concentration-dependent physicochemical reorganization of NaCMC/curcumin (CUR) systems was investigated using solvent-controlled conductometry and viscometry. Curcumin was introduced into aqueous NaCMC as a DMSO solution, and an independently measured NaCMC/DMSO system was used to discriminate CUR-associated effects from dilution and mixed-solvent effects. Progressive addition of DMSO alone produced a smooth nonlinear decrease in conductivity, whereas the CUR-containing system exhibited a pronounced discontinuity between 22.5 and 23.0 mL of CUR/DMSO addition, where conductivity decreased from 600.1 to 264.7 μS cm^-1 (-55.9%), followed by a reversal of the conductivity trend. The absence of an analogous transition in the DMSO control indicates that the discontinuity cannot be explained by solvent dilution alone and is consistent with the onset of a CUR-associated cooperative ionic/supramolecular reorganization within the coupled NaCMC/water/DMSO environment. Viscometric measurements further demonstrated a composition-dependent decrease in the hydrodynamic response of NaCMC upon CUR incorporation, indicating reorganization at the macromolecular level. Importantly, the observed conductivity and viscosity changes are interpreted as multicomponent responses involving solvent reorganization, ion solvation and counterion mobility, polymer hydration, macromolecular rearrangement, and CUR-dependent association rather than as evidence for a single fixed-stoichiometry NaCMC/CUR complex. These results establish a physicochemical framework in which curcumin incorporation induces coupled ionic and macromolecular reorganization of NaCMC and highlight the importance of solvent-matched controls for mechanistic interpretation of polysaccharide-polyphenol systems.