Observation of the dynamics of clusters in d-glucose with the use of dielectric spectroscopy

Abstract

Dielectric and FTIR measurements were performed on D-glucose in its supercooled liquid phase. The data obtained revealed that apart from the structural relaxation. a much slower relaxation mode exists in the liquid phase of D-glucose. Analysis of the dielectric data showed that this new mode exhibits features characteristic of the cluster relaxation process, i.e. the exponential relaxation function, as well as the equilibration time which is much longer than the relaxation time. Therefore we attributed this process to the long range correlation of density fluctuations (LRCDF). We also show that above T = 370 K the dielectric strength of the cluster relaxation starts to decrease rapidly. However FTIR measurements indicated that at T = 366 K reorganization of the liquid structure occurs. Combined dielectric and FTIR data showed that above T = 366 K clusters become less stable and probably disintegrate. Moreover the splitting temperature T_s = 387 K was determined from the dielectric data. Its value corresponds to the temperature T = 385 K at which the change of dynamics of the hydroxyl group (hydrogen bonds) is observed. It can be assumed that the change of dynamics of the D-glucose (at T_s) is related to the temperature at which LRCDF vanishes. It should be added that to the best of our knowledge this is the first dielectric study on dynamics of clusters in carbohydrates. Moreover, due to our studies the relaxation map of monosaccharides seems now to be complete.