Dielectric relaxation and molecular interaction analysis of ethanol–poly(ethylene glycol) (PEG200–PEG600) binary mixtures at 25 °C using time domain reflectometry

The dielectric relaxation behavior of ethanol–poly(ethylene glycol) (PEG200, PEG300, PEG400, and PEG600) binary mixtures was investigated at 25 °C over the frequency range 10 MHz to 30 GHz using time domain reflectometry (TDR). The complex permittivity spectra were analyzed using the Cole–Davidson model, with the symmetric broadening parameter (α) fixed at zero, indicating an asymmetric distribution of relaxation times. The static dielectric constant (ε0) decreased systematically with increasing PEG content, whereas the high-frequency dielectric constant (ε∞) exhibited a non-linear dependence on composition. The relaxation time (τ) showed a non-monotonic variation with minima at intermediate PEG fractions (ϕpeg ≈ 0.6–0.8), reflecting composition-dependent dipolar dynamics. The distribution parameter (β) decreased with increasing PEG molecular weight, indicating a broader distribution of relaxation environments. The excess dielectric permittivity (ε0E) and excess inverse relaxation time (1/τ)E exhibited both positive and negative deviations, confirming non-ideal mixing behavior arising from competing effects of dipolar correlation, hydrogen-bond interactions, and molecular mobility. The effective Kirkwood correlation factor (geff) remained greater than unity throughout the composition range, indicating persistent cooperative dipolar orientation. Bruggeman analysis revealed systematic deviations from ideal mixing, with the interaction parameter (a) varying with PEG molecular weight and reflecting differences in intermolecular interaction strength. Overall, the results demonstrate that the dielectric behavior of PEG–ethanol mixtures is strongly influenced by composition and PEG chain length, providing insight into the intermolecular interactions and relaxation dynamics governing these binary systems.