Structure of cellulose in cuoxam

Abstract

AbstractCuoxam ([CuII(NH3)4](OH)2) is a well known solvent for cellulose. Because of its deep blue colour, it has been used so far only for viscosity measurements. Direct light scattering measurements have not yet been reported in the literature.We carried out static and dynamic light scattering measurements in cuoxam using the blue wavelength of λ0 = 457.9 nm from an Argon ion laser. The measurements were involved with some difficulties mainly caused by colloidal particles of CuO and Cu(OH)2 which could be removed by direct centrifugation of the cells. Furthermore, the scattering intensity had to be corrected for extinction. The refractive index increment was taken from the literature.12 samples of different molecular weight and different origin were measured, and common power law behavior was found in a region up to about DPw = 1000 for both, the radius of gyration Rg and the hydrodynamic radius Rh, derived from the diffusion coefficient Dz. At higher degrees of polymerization characteristic deviations to lower radii occurred.These deviations are not caused by aggregation since the DPw's agreed with those from the cellulose tricarbanilates. The quantitative analysis of the radii and the angular dependence of the scattered light allowed determination of the chain stiffness. A Kuhn segment length of Ik = 25.6 (±6.2) nm and a characteristic ratio C∞ = 49.6 (±12.0) were derived. These values are close to those for cellulose‐tri‐carbanilate in dioxane.The reason for the increased stiffening is discussed on the basis of a special H‐bond model.