Study of molecular interaction in aqueous sucrose in the GHz region using Time Domain Reflectometry (TDR)

Abstract

Dielectric relaxation of aqueous sucrose [C12H22O11] has been carried out over the temperature range of 278.15 K to 298.15 K in the frequency region of 0.01 GHz to 30 GHz using time domain reflectometry technique (TDR). Two modes of relaxation processes were observed, namely low-frequency (primary) and high-frequency (secondary) relaxation. The rotating motion of sucrose molecules is primarily responsible for the low-frequency dispersion of relaxation, whereas the reorientation of bulk water is responsible for the high-frequency dispersion of relaxation. Dielectric parameters, i.e., static dielectric constant (εj), relaxation time (τj), dipole moment (û), Kirkwood factor of low frequency relaxation (g1), and thermodynamic parameters, i.e., free energy of activation (ΔFj), enthalpy of activation (ΔHj) and entropy of activation (ΔSj) were calculated. The static dielectric constant (εj), which was detected for both relaxation processes, i.e., ε1 and ε2, was shown to be decreasing with increasing temperature and solute molecule concentration. Over the course of all the concentrations used, it was observed that the τ1 and τ2 both increased with the sucrose concentration and also towards the low temperature. The decreasing trend of correlation factor (g1) suggests a strong possibility of antiparallel alignment of dipoles between sucrose molecules towards higher concentrations. Solute-solute antiparallel correlation seems to be reduced at lower temperature. Higher values of dipole moments at lower sucrose concentrations imply reduced antiparallel alignment between sucrose molecules, while lower values of effective dipole moments (μeff) obtained using Cavell and Kirkwood-Frohlich (KF) equations increase the likelihood of antiparallel alignment of sucrose dipoles. In terms of hydration dynamics, the total water molecules that are effectively locked by the sucrose molecules (Zib) were also calculated. Finally, dielectric parameters have been corroborated by thermodynamic parameters.