A dielectric study of a carboxymethylcellulose in aqueous solution

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Abstract
A carboxymethylcellulose sodium salt (CMC) with about 50% of the glucose units substituted, has been studied dielectrically by the “ellipsoid method” at various wave lengths. Aqueous solutions containing 0.1–0.0025 g./100 ml. were investigated. Dielectric increments of 2–9 dielectric constant units were obtained for these solutions. The calculated increment per gram per liter was not constant but increased considerably at the lowest concentrations, indicating the prevalence of polar molecules or aggregates at the lowest concentrations, whereas less polar aggregates dominate at higher concentrations (more than 0.01% solutions). At the lowest concentration studied, 0.0023%, the increment per gram per liter was about 120, corresponding to a molar increment of about 55,000,000. Dielectric dispersion curves were obtained which approached theoretical Debye dispersions, indicating that the CMC molecules are rather rigid. The dispersion curves were displaced toward shorter wave lengths with increasing concentration, probably due to the strong molecular interaction. At the lowest concentration a relaxation time of 4.6 × 10−7 sec. was calculated for the CMC molecule. This corresponds to a rotation of the molecules about their long axes in the electric field. An average molecular weight of about 460,000 was calculated for the CMC molecules, or polar aggregates, in very dilute aqueous solution. The electric moment of CMC was estimated to be about 1000 Debye units. In contrast to CMC, the uncharged polysaccharides dextran and ethyloxyethylcellulose did not show any deviation of the dielectric constant values from that of the pure solvent, when investigated in 0.5% aqueous solutions at various wave lengths. It was concluded that the dielectric properties of CMC are very similar to those of other polyelectrolytes studied–such as desoxyribonucleic acid, nucleohistone, and hyaluronic acid.

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