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The dielectric behavior of a thermo-sensitive poly-(N-isopropylacrylamide) (PNIPAM) microgel suspension with a dense concentration was investigated over the frequency range of 40 Hz to 110 MHz in a wide temperature window of 10-60 °C. By successfully removing the electrode polarization effect from the original data, two remarkable and temperature-dependent relaxation processes were observed. Both of the two-phase transition processes, i.e., the colloidal crystal-to-liquid transition, which has not yet been detected by dielectric spectroscopy before, as well as the volume phase transition, were detected by the relaxation parameters. Based on the three physical states of the microgel suspension, the relaxation mechanisms are discussed in detail. The slow relaxation originates from the segmental motion and the counterion motion along the polymer chain over the whole temperature range. It was found that when the system is in the colloidal crystal and liquid state, the segmental motion is cooperative with side chain and hydrogen bonding networks, while in the phase separation state (at temperatures above the lower critical solution temperature (LCST)), the cooperative interaction disappears. The fast relaxation is due to the fluctuation of counterions below the LCST and the interfacial polarization above the LCST. Based on interfacial polarization theory, which describes the dielectric model of a conventional particle dispersion, the temperature dependence of the electrical properties for the constituent phases (the permittivity, conductivity and volume fraction of the microgel (ε, κ, ϕ); the conductivity of the medium water (κ); the water content in the PNIPAM microgel (f)) were calculated using the Hanai equation. The water content is close to the result obtained using light scattering, indicating that the dielectric model for a conventional particle dispersion is also applicable to a soft atypical colloidal dispersion.

Dielectric measurements were carried out on binary mixtures of Triton X-100 (TX-100, a nonionic surfactant with a polyoxyethylene chain) and 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF(4)], a hydrophilic ionic liquid), and [bmim][BF(4)]/TX-100/cyclohexane microemulsions in a wide frequency range to study the molecular interaction and percolation in these systems. Striking dielectric relaxations were observed, and the dc conductivity data were obtained from the measured total dielectric loss spectra. The interaction between TX-100 and [bmim][BF(4)] is estimated by analyzing the dc conductivity of TX-100/[bmim][BF(4)] solutions in light of the Bruggeman's effective medium approximation, which indicates that spherical micelles are formed when the TX-100 volume fraction is below 48% and the number of cations associated with every TX-100 molecule is eight. For IL-oil microemulsions, both the dependence of dc conductivity and the permittivity (for fixed frequency) on cyclohexane concentration were used to identify the oil-in-IL, bicontinuous, and IL-in-oil microregions. Both the conduction and dielectric relaxation behavior suggest that a static percolation occurs in this hydrophilic IL microemulsion.