title: Amorphous supramolecular structure of carboxymethyl cellulose in aqueous solution at different pH values as determined by rheology, small angle X-ray and light scattering.
abstract: 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.
authors.affiliation: Biotechnical Faculty of Ljubljana University, Chair of Microbiology, Večna pot 111, 1000 Ljubljana, Slovenia.
authors.forename: Iztok
authors.initials: I
authors.lastname: Dogsa
authors.affiliation: Faculty of Chemistry and Chemical Technology, University of Ljubljana, Chair of Physical Chemistry, Aškerčeva 5, 1000 Ljubljana, Slovenia.
authors.forename: Matija
authors.initials: M
authors.lastname: Tomšič
authors.affiliation: JUB-H d. d., Dol pri Ljubljani 28, 1262 Dol pri Ljubljani, Slovenia.
authors.forename: Janez
authors.initials: J
authors.lastname: Orehek
authors.affiliation: Faculty of Chemistry and Chemical Technology, University of Ljubljana, Chair of Physical Chemistry, Aškerčeva 5, 1000 Ljubljana, Slovenia.
authors.forename: Elizabeta
authors.initials: E
authors.lastname: Benigar
authors.affiliation: Faculty of Chemistry and Chemical Technology, University of Ljubljana, Chair of Physical Chemistry, Aškerčeva 5, 1000 Ljubljana, Slovenia.
authors.forename: Andrej
authors.initials: A
authors.lastname: Jamnik
authors.affiliation: Biotechnical Faculty of Ljubljana University, Chair of Microbiology, Večna pot 111, 1000 Ljubljana, Slovenia. Electronic address: david.stopar@bf.uni-lj.si.
authors.forename: David
authors.initials: D
authors.lastname: Stopar
mesh_terms: D002266:Carboxymethylcellulose Sodium / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D008027:Light; D012212:Rheology; D012542:Scattering, Radiation; D053838:Scattering, Small Angle; D014867:Water / Q000737:chemistry*; D014961:X-Ray Diffraction
chemical_list: D014867:Water; D002266:Carboxymethylcellulose Sodium
keywords: CMC; Carboxymethyl Cellulose; DLS; Macromolecular structure; SAXS; String-of-beads model; Supramolecular structure