Physico-Chemical nanomaterials science

Influence of ions on dielectric properties of nanostructured water-cellulose-NaCl systems in a wide temperature range.

D.O. Shevtsov1, M.M. Lazarenko1, О.М. Alekseev1, V.A. Barbash 2, K.S. Yablochkova1, V.I. Kovalchuk1, S.G. Nedilko1 , V.P. Scherbatskyi1, 
D.A. Andrusenko1, M.V. Lazarenko3

1 Taras Shevchenko National University of Kyiv, Faculty of Physics, Volodymyrs’ka St. 64/13, Kyiv 01601, Ukraine.
E-mail: shevadima15z@gmail.com
2 National Technical University of Ukraine “Igor Sikorsky Kyiv Polytechnic Institute”, prospect Peremogy 37, Kyiv, Ukraine 
3National University of Food Technologies, Volodymyrs’ka St. 68, Kyiv-01601, Ukraine.

The lyotropic liquid-crystalline phases in water suspensions of cellulose nanocrystals have received much attention, leading to the extensive research of their liquid state rheological, optical, and structural properties. However, few researchers have studied the properties of water-nanocellulose systems in the solid state. Moreover, existing data mainly concerns the nanocellulose films with low water concentrations.
An essential feature of the solid water-nanocellulose system structure is the spatial heterogeneity of its nanocrystals, which arises when samples are prepared by evaporation or freezing. Different types of ionic impurities  concentrate in inter-crystalline layers of ice or cellulose nanocrystals, which can significantly affect phase transitions and relaxation processes. Therefore, the study of the physical properties of water-nanocellulose systems in the temperature region near the phase transition constitutes a significant interest. 
Our present work discusses the properties of the water-nanocellulose-NaCl systems studied by dielectric spectroscopy and optical spectroscopy methods. We report that a dielectric relaxation is observed in water-nanocellulose-NaCl systems in the temperature range of [–100¸ 0] оС, and that nature of this process differs from the dielectric relaxation in water and water-nanocellulose systems. The relaxation process in water-nanocellulose-NaCl solutions can be attributed to the surface layers of cellulose nanocrystals, which are surrounded by a hydrate shell. Temperature decrease in the dielectric relaxation of the water-nanocellulose-NaCl system in comparison with the water-nanocellulose systems associated with the influence of ions on the hydrogen bonds system. The obtained data are in agreement with the results of photoluminescence and optical transmission studies.