Dielectric Relaxation of Aqueous Glycine Investigated by Time-domain Reflectometry

Abstract

The dielectric response of aqueous glycine was examined from 10 MHz to 30 GHz at seven nominal temperatures between 25 and −5 °C over a reported composition series of 0–1.0 mol L⁻¹. Time-domain reflectometry data were interpreted with a single Cole–Davidson relaxation function to obtain static permittivity (ε₀), relaxation time (τ), high-frequency permittivity (ε∞), and the distribution parameter (β). At 25 °C, the reported ε₀ increased from 78.27 for water to 105.35 at the highest glycine concentration, while τ increased from 8.32 to 16.08 ps. Both parameters generally increased on cooling. An Eyring analysis performed by ordinary least-squares regression of the tabulated relaxation times yielded activation enthalpies ranging from approximately 8.53 to 10.89 kJ mol⁻¹ and concentration-dependent activation entropies. The reported Kirkwood correlation factor at 25 °C decreased from 2.82 for water to 1.57 at 8.9 wt% glycine, indicating a change in the effective orientational correlation under the adopted molecular model. The dielectric and thermodynamic trends are consistent with concentration- and temperature-dependent solute–solvent dynamics, although the fitted parameters alone do not uniquely establish a hydrogen-bonding mechanism or exclude multiple relaxation processes. Interpretation at subzero temperature is conditional on the uncharacterized sample phase.