Amorphous supramolecular structure of carboxymethyl cellulose in aqueous solution at different pH values as determined by rheology, small angle X-ray and light scattering

•The supramolecular structure of CMC was represented as a set of subspaces with different densities.•CMC is most expanded, has the largest Rg, persistence length, and size of heterogeneous regions at pKa.•Most CMC molecules reside in a few high density subspaces below pKa.•Above the pKa the CMC molecules are approximately uniformly distributed.•SAXS, SLS, DLS, microscopy and viscosimetry give coherent view of CMC structure from 1nm to 100μm scale. Carboxymethyl cellulose (CMC) is one of the most widely used thickening agents in industry. The combination of small-angle X-ray scattering (SAXS), static and dynamic light scattering, as well as viscosity measurements and microscopy at different pH values was utilized to explore the physicochemical properties of CMC on a scale ranging from individual macromolecules to supramolecular assemblies. The supramolecular structure of CMC was represented as a set of characteristic sample subspaces based on SAXS data utilizing the string-of-beads model. The results indicate that at pH 7.0 individual CMC molecules are approximately uniformly distributed in a supramolecular structure owing to strong intra- and intermolecular repulsive interactions. The structure of CMC is most expanded at the value of pKa, where it has the largest radius of gyration, persistence length, and size of heterogeneous regions. Below pKa the majority of the CMC sample volume belongs to the low density subspaces. Most of CMC molecules, however, reside in a few high density subspaces. Dynamically, supramolecular structure of CMC is composed of fast diffusive relaxation processes embedded in a background of non-diffusive slow relaxation process at high pH and mostly slow relaxation processes at low pH. The rheological properties of CMC at different pH values were directly related to the CMC supramolecular structure in the aqueous environment.