Satoru Mashimo

Time domain reflection methods for dielectric measurements to 10 GHz

Total reflection methods and instrumentation for their use are described for measurements of dielectric permittivity and loss at frequencies to 10 GHz or more. Several cell designs are shown, together with analyses of their performance. Procedures are given for correcting effects of wave propagation in the cells and residual reflections in the cells by bilinear analysis with calibrations using dielectrics of known permittivity. Representative results are presented for highly polar liquids, dilute solutions of polar molecules in nonpolar solvents, electrolyte solutions, and ionic glasses with appreciable ohmic conduction.

Structures of water and primary alcohol studied by microwave dielectric analyses

By the use of the time domain reflectometry method dielectric measurements were carried out first on methanol mixtures with ethanol and 1‐propanol, and second, water mixtures with methanol, ethanol and 1‐propanol in the frequency range 10 MHz–20 GHz. The first mixtures show a Debye relaxation and logarithm of the relaxation time is given by a linear function of the mole fraction of methanol. These mixtures have the same chainlike cluster of pure alcohol. The second mixtures show the same trend of the relaxation time in a region 0≤xw 0.83 and that the cluster must be cyclic, consisting of six molecules.

The dielectric relaxation of mixtures of water and primary alcohol

Dielectric measurements over a microwave frequency range 10 MHz–15 GHz were carried out by the use of new time domain reflectometry equipment on the mixtures of water with five primary alcohols, viz., methanol, ethanol, and n‐propanol in the concentration range 0≤x≤1 and n‐butanol and amyl alcohol in the range 0≤x≤0.5 at room temperature; x being the mole fraction of water. The systems of water and two alcohols of low molecular weight are characterized by a single relaxation with a distribution parameter of the unity or near to it. The molecular reorientation in the mixtures as well as water and these alcohols is a cooperative process involving a large number of molecules with the hydrogen‐bond linkages (O–H⋅⋅⋅O). Dielectric behavior of the mixtures of water and methyl or ethyl alcohol is due to the structure of a hydrogen‐bonded network being microscopically homogeneous. Microscopic heterogeneity occurs in the mixtures of water and higher alcohols.

The structure of water determined by microwave dielectric study on water mixtures with glucose, polysaccharides, and L-ascorbic acid

Dielectric relaxation measurements over an extremely wide frequency region from 1 MHz to 20 GHz were performed on water mixtures with glucose, polysaccharides, and L‐xylo ascorbic acid by the use of time domain reflectometry. For mixtures of polysaccharides bigger than maltotriose, two relaxation peaks were definitely observed. The high frequency relaxation is the water relaxation and the low frequency one is due to orientation of polysaccharide molecules. In the case of glucose, only one relaxation peak could be observed. It is shown that a hexagonal cluster in the lattice of ice can be replaced easily by the glucose molecule, where the lattice is distorted slightly, but stabilized by several hydrogen bonds between the glucose molecule and the lattice. Although the cluster can be replaced by the L‐ascorbic acid molecule too, the lattice cannot be kept stable. Its water mixture shows two relaxation peaks clearly. It is suggested that water has a structure of the distorted lattice of ice. Fluctuation of th...

Dielectric relaxation measurements of poly(vinyl acetate) in glassy state in the frequency range 10−6–106 Hz

Dielectric relaxation measurements covering a wide frequency range extending from 10−6 to 106 Hz were made on poly(vinyl acetate) with conventional glass transition temperature Tg of 31 °C at temperatures between 26.85 and 84.77 °C. It was found that temperature dependence of frequency of the maximum dielectric loss below Tg cannot be described by the Williams–Landel–Ferry equation which gives a complete explanation to the dependence in the temperature range sufficiently higher than Tg, but by a simple expression of Arrhenius type with activation energy 138 kcal/mol. It was also found that distribution of the relaxation times changes abruptly in the vicinity of Tg. Potential barrier height for the chain motion has a distribution to some extent below Tg.

Evaluation of complex permittivity of aqueous solution by time domain reflectometry

Abstract A time domain reflectometry (TDR) method has been developed in order to measure dielectric relaxation process with a weak relaxation strength of the order of 0.1 in aqueous solution. Application of the TDR measurement have been made for poly(L-glutamic acid) in aqueous solution, which exhibits a helix-coil transition with changing the pH value. Dielectric relaxation process observed around 100MHz shows a definite transition in its strength in the vicinity of pH=6. The TDR method has been also applied to a DNA in aqueous solution with 0.1SSC buffer. A double helix structure of DNA melts at about 75°C to a coiled structure. Relaxation process around 100MHz shows a transition in the strength and also in the relaxation time around this temperature. In both cases, relaxation process caused by water molecules could be observed separately from the process observed around 100MHz. The relaxation strength and the relaxation time are nearly the same as those of the free water. A bilinear analysis developed by Cole has been used to measure methanol-water mixtures. A relaxation process could be observed continuously with the composition. It has been concluded that the bilinear analysis is quite powerful if the present TDR method is used together for the dielectric measurement covering a wide frequency region from 1MHz to 15GHz.

The structure of water and methanol in p-dioxane as determined by microwave dielectric spectroscopy

Dielectric measurements were performed on water–p‐dioxane and methanol–p‐dioxane mixtures using time domain reflectometry over the frequency range 0.1–10 GHz. In the case of water–p‐dioxane mixtures, the relaxation strength normalized by the number of water molecules per unit volume is independent of the molar fraction of water xW if xW 0.66. However, the relaxation time of pure methanol is too large for clusters consisting of three molecules. It is suggested that the chainlike clusters form network structures.

Dielectric study on dynamics of water in polymer matrix using a frequency range 106–1010 Hz

Dielectric measurements were made on polyethylene glycol (PEG) and polyvinyl pyrolidone (PVP)–water systems over a frequency range 106 –1010 Hz by a time domain reflectometry. Two relaxation peaks were observed in the PVP system. The high frequency process is caused by rotational diffusion of water clusters and concentration dependence of the relaxation time is well explained by the free volume theory. The low frequency process is attributed to water molecules bound to the polymer and its relaxation time is reasonably irrespective of the concentration. On the other hand, the PEG system shows a single relaxation process which is caused by the rotational diffusion of water clusters. A sign of the segmental motion was recognized barely for highly concentrated system of PEG.

High order and local structure of water determined by microwave dielectric study

Water mixture with tert‐butanol shows two critical points if the logarithm of dielectric relaxation time is plotted against the mol fraction of water XW. One point at XW∼0.97 is suggested to indicate the break point of a high order structure of water and another point XW=0.83 is that of a local structure. Existence of the high order structure was already indicated by a recent dielectric study on water–glucose mixture. The structure is a less ordered lattice of ordinary ice type. It is also shown that water mixture with treharose or maltose exhibits one relaxation peak as well as the glucose mixture. This manifests that the diameter of the water cluster is nearly the same as the length of treharose or maltose, at least, smaller than that of maltotriose which shows two relaxation peaks. The critical point XW∼0.97 corresponds to about 30 water molecules included in the high order structure, which is very reasonable to compare the result of the glucose mixture.

Dielectric relaxation of poly(vinyl acetate)

Dielectric relaxation measurements of undiluted and diluted poly(vinyl acetate) PVAc have been made at temperatures 288<T<366 K over an extremely wide frequency range from 1 μHz to 150 MHz. The complex permittivity can be described quantitatively by the Havriliak–Negami equation e*=e∞+Δe[1+(jωτ0)β]−α, 0<α, β≤1. It has been found that the parameter α is given by a linear equation of dipole moment ratio g as α=1.09–0.91g. This observation suggests that α is connected closely with local chain conformations. On the other hand, β is nearly constant ∼0.87 above the glass transition temperature and is independent of effect of the diluent. This suggests that the constant value of β is an inherent characteristic of the relaxation spectrum of PVAc.