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Various relaxation procedure in the supercooled state of D-xylose have been investigated using dielectric spectroscopy over a wide frequency (1 mHz – 10 MHz) and temperature range (140-350 K). The main relaxation process (α) that is accountable for the glass transition phenomena, another secondary relaxation process is also visible below glass transition temperature. The attached hydroxymethyl (-CH2OH) side group to the sugar ring might be responsible for this process. In addition, we have applied Coupling model to find the location of intermolecular relaxation below the glass transition temperature (Tg). The dependence of various dielectric parameters viz. τα, τβ, τγ and τβ cm on temperature have been critically examined. The current experimental result shows that, log10 σdc vs. log10 τα dependence is nonlinear and hence can be described with the fractional Stokes-Einstein-Debye relation.

High frequency dielectric spectroscopy has been used to investigate the dielectric behavior of the pure as well as the aqueous solutions of 2-ethyl-1-hexanol at 270 and 300 K. It was found that the strength of Debye peak decreases systematically with increasing concentration of water. This behavior has been explained on the basis of the fact that alcohol favors more reduced structure in presence of water. This result is consistent with the simulation work as well as low frequency dielectric results on alcohol-water system.

Using broadband dielectric spectroscopy, we have studied different types of relaxation processes, namely, primary (α), secondary (β), and another sub-Tg process called γ-process, in the supercooled state of d-lyxose, over a wide frequency (10-2-109Hz) and temperature range (120-340 K). In addition, the same sample was analyzed by differential scanning calorimeter. The temperature dependence of the relaxation times as well as the dielectric strength of different processes has been critically examined. It has been observed that the slower secondary relaxation (designated as β-) process shifts to lower frequencies with increasing applied pressure, but not the faster one. This pressure dependence indicates that the observed slower secondary relaxation (β-) is Johari-Goldstein relaxation process and faster one (γ-process) is probably the rotation of hydroxymethyl (-CH2OH) side group attached to the sugar ring, that is, of intramolecular origin. © 2011 Elsevier Ltd. All rights reserved.

Binary water mixtures usually display a water relaxation (process II) which can be studied by broadband dielectric spectroscopy (BDS) at subzero temperatures. In a large collection of binary water mixtures, a slight increase of the relaxation strength is observed for low water concentration, whereas a faster increase is seen above a critical concentration. The assumption behind this result is that at high water concentration self-associations of water molecules are present in the solutions. In this work, we have studied poly(propylene glycol) water solutions by means of broadband dielectric spectroscopy and Fourier transform infrared spectroscopy (FTIR) using the attenuated total reflectance method (ATR) in the temperature range of 120-300 K. By combining both techniques, we found a critical water concentration x w = 0.20 above which the relaxation strength of the water relaxation (process II) increases more rapidly than at low water concentration indicating the self-association of water molecules. © 2011 American Chemical Society.

The dielectric relaxation behavior of D-arabinose aqueous solutions at different water concentrations is examined by broadband dielectric spectroscopy in the frequency range of 10-2-107 Hz and in the temperature range of 120-300 K. Differential scanning calorimetry is also performed to find the glass transition temperatures (Tg). In addition, the same solutions are analyzed by Fourier transform infrared (FTIR) spectroscopy using the attenuated total reflectance (ATR) method at the same temperature interval and in the frequency range of 3800-2800 cm-1. The temperature dependence of the relaxation times is examined for the different weight fractions (xw) of water along with the temperature dependence of dielectric strength. Two relaxation processes are observed in the aqueous solutions for all concentrations of water. The slower process, the so-called primary relaxation process (process-I), is responsible for the Tg whereas the faster one (designated as process-II) is due to the reorientational motion of the water molecules. As for other hydrophilic water solutions, dielectric data for process-II indicate the existence of a critical water concentration above which water mobility is less restricted. Accordingly, FTIR-ATR measurements on aqueous solutions show an increment in the intensity (area) of the O-H stretching sub-band close to 3200 cm-1 as the water concentration increases., Funded by: Spanish Ministry of Education. Grant Number: MAT-2007-63681; European Union. Grant Number: 502235-2; SOFTCOMP and Basque Government. Grant Number: IT-436-07.

A two-channel impedance technique has been used to study the relaxation behavior of 2-ethyl-1-hexanol with polar and non-polar dopants at the few percent concentration level over a wide temperature and frequency range. The non-polar dopants shift both the Debye and the primary structural relaxation time in the same direction, to shorter times for 3-methylpentane and to longer times for squalane, consistent with the relative glass transition temperatures (Tg) of the components. By contrast, polar dopants such as water or methanol modify the α-process towards slower dynamics and increased amplitude, while the Debye process is accelerated and with a decreased amplitude. This effect of adding water to alcohol is explained by water promoting more compact structures with reduced Kirkwood correlation factors. This picture is consistent with a shift in the neutron scattering pre-peak to lower scattering vectors and with simulation work on alcohol-water systems.