Cellulose molecular properties in 1-alkyl-3-methylimidazolium-based ionic liquid mixtures with pyridine

A study of the viscometric and dynamooptical (flow birefringence) properties of cellulose samples in mixtures of 1-alkyl-3-methylimidazolium-based ionic liquids with pyridine was carried out. It was established that the mixtures provide stable molecular dispersed cellulose solutions which are suitable for the determination of the characteristics of the dissolved macromolecules. The viscous and dynamooptical properties of cellulose in ionic liquid/pyridine mixtures, cadoxen (CdO/ethylenediamine), and in cadoxen/water at low solute concentrations were compared, and the behavior of cellulose in these solvents was discussed. It was found that the values of the refractive index of 1-alkyl-3-methylimidazolium-based ionic liquid/pyridine mixtures are close to the refractive index of cellulose in their media. The extremely low refractive index increment (|dn/dc| = (0.004 ± 0.001) cm3 g−1) for cellulose in 1-ethyl-3-methylimidazolium diethylphosphate and pyridine ([EMIM]Et2PO4/pyridine (1:1)) allowed to confirm that the cellulose monomer unit is not optically isotropic and is characterized by a small in value and positive in sign anisotropy of polarizability (Δa = +1.0 × 10−25 cm3).