Broadband Dielectric Spectroscopic, Calorimetric, and FTIR‐ATR Investigations of D‐Arabinose Aqueous Solutions

Abstract

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) -10(7) Hz and in the temperature range of 120-300 K. Differential scanning calorimetry is also performed to find the glass transition temperatures (T(g)). 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 (x(w)) 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 T(g) 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.

Glass transition phenomena in D-xylose aqueous solutions: A broadband dielectric spectroscopy study

“…This suggests that water molecules which are very close to D-xylose are tightly bound to the D-xylose molecules, whereas the water molecules that are far from the D-xylose molecules, called loosely bound water molecules will continue to enjoy reorientational freedom even below T g , which is identified as process-II. Similar conclusions were also drowned by various researchers in different aqueous solutions [2][3][4].…”

“…Figure 3(b) clearly indicates that D-xylose-water solutions show two-relaxation processes, the lower frequency one (process-I) which is arrested at glass transition temperature (T g ) discussed above, whereas the high frequency process designated as process-II show Arrhenius type temperature dependence below T g . Similar behavior was also observed in several other aqueous solutions [2][3][4]. These similar properties suggest that process-II in D-xylose aqueous solutions is due the reorientational motion of water molecules in these mixtures.…”

“…Representative fit results for this binary system at a fixed temperature are shown in Figure 2(b). From this figure, it is clear that the nature of the low frequency process (process-I) is similar to those observed in pure glass formers as well as hydrated samples [2][3][4]6,7]. This indicates that it is due to the cooperative motion of homogeneous mixture which is plasticized and becomes faster in the presence of water.…”

“…Since the water molecule has a big dipolar moment, dielectric spectroscopy is a very adequate technique to analyze the reorientational dynamical behavior of water on a broad frequency range. Thus, a lot of attention has been made in the literature to the dielectric behavior of water dynamics in several aqueous mixtures [2][3][4].…”