Hydrogen bond network restructuring in water: Dielectric spectroscopy insights from dissolved gas studies

This study investigates the relationship between dissolved gases, particularly nitrogen, and the complex permittivity of liquids under test (LUTs). Measurements were conducted using an open-ended coaxial probe positioned inside a pressure vessel containing the LUT. Pressures ranged from 1 to 16 bar absolute, with frequency measurements between 0.5 to 10 GHz. A significant increase in the real relative permittivity ( ε ′ ) was observed in aqueous solutions, while the loss factor ( ε " ′ ) exhibited less significant changes. Conversely, non-aqueous liquids with inherently low permittivity, such as olive oil and propan-2-ol, displayed negligible changes, remaining within the measurement uncertainty. Although an increase in ε ′ was consistently observed, its magnitude varied across repeated experiments. At 5 bar in pressurised deionised water or saline solutions, approximately 60 % of experiments showed around a 4 % increase in ε ′ , while the remainder exhibited a lower increase of around 2 %. Similarly, aeration of deionised water at atmospheric pressure produced an approximate 3 % increase in ε ′ across the entire frequency range. The increase in complex permittivity was proportional to aeration time, stabilising after 30–60 min. Temperature fluctuations remained insignificant throughout all experiments, and the compressive effects of pressurisation on the LUT’s complex permittivity were confirmed to be negligible. The observed permittivity changes were attributed to the restructuring of water’s hydrogen-bond network around small hydrophobic solutes. • Gases were dissolved either via pressurisation or aeration at atmospheric pressure. • A significant increase in ε ′ of water was observed upon dissolution of gases. • A less significant increase was observed in ε " ′ . • A slim form open-ended coaxial probe was used for measurements. • The changes in complex permittivity were attributed to hydrophobic hydration.