Dielectric relaxation and molecular interactions in ethylene glycol–1-propanol binary mixtures at microwave frequencies

Dielectric relaxation behavior of ethylene glycol–1-propanol (EG–PR) binary mixtures was investigated using time domain reflectometry over a frequency range of 10 MHz to 30 GHz at temperatures of 10 °C, 15 °C, 20 °C, and 25 °C. Eleven compositions were studied to understand the influence of molecular interactions and hydrogen bonding on dielectric properties. The complex permittivity spectra were analyzed using the Havriliak–Negami model, revealing Cole–Davidson-type relaxation. The static dielectric constant (ε0) increased with EG concentration, while relaxation time (τ) decreased, reflecting faster dipolar reorientation in EG-rich mixtures. Negative excess permittivity and deviations in excess inverse relaxation time indicated strong non-ideal behavior due to specific intermolecular interactions. Kirkwood correlation factors (gₑff >1) and Bruggeman factor deviations confirmed cooperative dipolar alignment and structural heterogeneity. Arrhenius analysis showed thermally activated relaxation with composition-dependent activation energies. The results highlight the critical role of hydrogen bonding and molecular associations in governing dielectric response, providing insight into the cooperative dynamics and non-ideal mixing behavior of polar binary liquids