Dielectric properties of model BaTiO3/polymer composites were measured over a broad frequency and temperature range. A series of BaTiO3/monomer suspensions were photocured into thin wafers. The wafers were equipped with aluminum electrodes, and the dielectric permittivity of the composites was investigated at frequencies from 100 Hz to 10 GHz and at temperatures from -140 to +150 °C. It has been found that for the same BaTiO3 loading dielectric characteristics of the composites strongly depend of the type of polymer. Polar polymers increase dielectric constant of the composites at low frequencies but have little effect at gigahertz frequencies. Dielectric losses of the composites show a maximum at some intermediate frequency within megahertz to gigahertz range that reflects the relaxation behavior of the polymer matrix. The magnitude of the losses increases with increasing polarity of the polymer component. At constant frequency and temperature, the composites follow a linear relationship between logarithm of their dielectric constant and volume fraction of the ferroelectric filler. Practical implications of such composites behavior are discussed.

Dielectric relaxation measurements on the methanol-water mixtures for the entire concentration range were carried out using time domain reflectometry in the frequency range from 500 MHz to 25 GHz at 20, 25, and 30°C. The excess partial molar activation free energy, enthalpy, and entropy for methanol, ⌬G MA E , ⌬H MA E , and ⌬S MA E , and those for water, ⌬G W E , ⌬H W E , and ⌬S W E , were calculated from accurately measured concentration and temperature dependence of the dielectric relaxation time of the mixtures. The behavior of the excess partial molar quantities in the regions below and above X ͑molar fraction of methanol͒ ϳ0.3 are quite different from each other. In a water-rich region, ⌬H MA E and ⌬S MA E exhibit two maxima at Xϳ0.045 and Xϳ0.12, which is clearly attributed to structural enhancement of the hydrogen bond network of water, the so-called hydrophobic hydration. Appearance of two maxima in ⌬H MA E and ⌬S MA E implies that water molecules surround methanol molecules in qualitatively different manners around the two points. In the concentrated region of Xу0.3, the values of ⌬H MA E and ⌬S MA E become nearly zero, which means that methanol molecules in the mixtures find themselves in not a very different environment from that in pure methanol, associated and forming chainlike clusters. Water molecules seem to exothermically attach to the hydrophilic site of methanol.

Dielectric relaxation measurements on the ethanol–water mixture for the entire concentration range in very small increments were carried out using TDR in the frequency range from 300 MHz to 25 GHz at 20 °C, 22.5 °C, and 25 °C. The activation enthalpy ΔH and entropy ΔS for the mixtures were separated from the activation free energy ΔG, and hence the excess partial molar activation free energy, enthalpy, and entropy for ethanol, ΔGEAE, ΔHEAE, and ΔSEAE, and those for water, ΔGWE, ΔHWE, and ΔSWE were calculated. The concentration dependence of these partial molar quantities shows the existence of two regions bound at X (molar fraction of ethanol) ∼0.18. In the water-rich region of X<0.1, ΔHEAE and ΔSEAE take large positive values, exhibiting two sharp maxima at X=0.04 and X=0.08, which is clearly attributed to structural enhancement of the hydrogen bond network of water by ethanol, the so-called hydrophobic hydration. From a standpoint of dynamics, mixing schemes of ethanol and water around the two points X=0.04 and X=0.08 seem to be qualitatively different. On the other hand, in the region of X>0.18, the values of ΔHEAE and ΔSEAE take nearly zero. This means that ethanol molecules in the mixtures are in almost the same environment as those are in pure ethanol, forming chainlike clusters surrounded or exothermically attached to by water molecules.

Dielectric relaxation measurements on water solutions of ethylene glycol 200 and 400, (degree of polymerization N=4 and 9) in entire concentration region were carried out using a time domain reflectometry at 25 °C in the frequency range from 300 MHz to 20 GHz. For all the samples, only one dielectric loss peak was observed in this frequency range. Plots of the relaxation strength and logarithm of the relaxation time calculated from apparent peak frequency of dielectric loss curves against monomer unit molar fraction of ethylene glycol X give straight lines in the region of 0<X<0.35 for N=4, and 0<X<0.37 for N=9. Shapes of dispersion and absorption curves exhibit critical change at the concentration X≈0.35 for N=4 and X≈0.37 for N=9, corresponding to the ratio of one ether oxygen and 1.7 water. Analysis of these phenomena indicates that hydration complex of one ether oxygen and 1.7 water is formed, and the 1:1.7 complex behaves as one kind of component corresponding to 2.7(=1+1.7) waterlike molecules in the solution. It is suggested that ether oxygen can be inserted into water structure by replacing water oxygen. This hydration mechanism makes water structure stable. Ethylene glycol dissolves in water without much perturbation to water structure.

Using time domain reflectometry, we carried out dielectric relaxation measurements on 1-propanol–water mixtures for the entire concentration range in the frequency range 100 MHz–25 GHz at 20, 25, and 30 °C. We have calculated the excess partial molar activation free energy, enthalpy, and entropy for 1-propanol, ΔG1PAE, ΔH1PAE, and ΔS1PAE, and those for water, ΔGWE, ΔHWE, and ΔSWE from the relaxation times. In the region of X (molar fraction of 1-propanol) ⩾0.14, ΔH1PAE and ΔS1PAE take nearly zero. This means that 1-propanol molecules in the mixtures find themselves in not a very different environment from that in pure liquid. In the water-rich region, ΔH1PAE and ΔS1PAE exhibit two maxima at X∼0.03 and X∼0.06, corresponding roughly to 0.9 and 0.78 g/cm3 of water content, respectively. This fact, together with the results of the molecular dynamics studies of Sciortino et al. suggest the formation of two kinds of saturated hydration structures: the clathrate hydration shells with tetrahedral local arrangements of water molecules around X∼0.03 and nonclathrate shells with large cavities with three-coordinated local arrangements around X∼0.06. Hydrophobic hydration seems to partly share the same mechanism with structural enhancement in pure water by lowering local density.

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Complex permittivity measurements were performed on sorbitol, xylitol, and sorbitol-xylitol mixture in the supercooled liquid state in an extremely wide frequency range from 10 microHz to 500 MHz at temperatures near and above the glass transition temperature. We determined detailed behavior of the relaxation parameters such as relaxation frequency and broadening against temperature not only for the alpha process but also for the beta process above the glass transition temperature, to the best of our knowledge, for the first time. Since supercooled liquids are in the quasi-equilibrium state, the behavior of all the relaxation parameters for the beta process can be compared among the polyols as well as those for the alpha process. The relaxation frequencies of the alpha processes follow the Vogel-Fulcher-Tammann manner and the loci in the Arrhenius diagram are different corresponding to the difference of the glass transition temperatures. On the other hand, the relaxation frequencies of the beta processes, which are often called as the Johari-Goldstein processes, follow the Arrhenius-type temperature dependence. The relaxation parameters for the beta process are quite similar among the polyols at temperatures below the alphabeta merging temperature, T(M). However, they show anomalous behavior near T(M), which depends on the molecular size of materials. These results suggest that the origin of the beta process is essentially the same among the polyols.

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