Toshihiro Umehara

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 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...

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.

Microwave Dielectric Study on Water Structure and Physical Properties of Aqueous Systems Using Time Domain Reflectometry with Flat-End Cells

Microwave dielectric measurements were performed in the frequency range from 1 mHz up to 30 GHz using a time domain reflectometry (TDR) method for emulsions and gels. Flat-end sample cells have been used in the TDR measurement to contact a small spot of the surface of those viscoelastic and solid samples without any destruction. Relaxation processes due to various water structures were observed for these aqueous systems. Relaxation parameters thus obtained offer information about these water structures and amounts. The relaxation strength obtained from the high frequency process due to free water can be an adequate measure of water content in spite of some ambiguities for different water structures in some materials. Comparisons of actual water contents in emulsion with those estimated from the relaxation strength indicate that water structure is affected by the interaction between water and micelle. Unfreezable water observed in DNA gel under the freezing point consists of bound water and a fraction of free water. Bound water molecules are still unfreezable to keep the double helical structure of DNA, when the fraction of free water is frozen at lower temperatures. These water structures determine physical properties of moist materials. TDR measuring technique with the flat-end cell is effective to investigate water structures in viscoelastic moist materials and to evaluate physical properties and structures of complex molecular systems.

Dielectric dispersion of primary alcohols in polymer complex

Dielectric measurements using a frequency region 106–1010 Hz were performed on methanol and ethanol‐polyvinyl pyrolidone systems by a time domain reflectometry. Two relaxation peaks were observed for each system. The high frequency process is the primary process of the alcohols. Relaxation time varies little with the polymer concentration. In the case of the ethanol system, its extrapolated value for pure polymer is 280 ps and does not differ much from the value of 130 ps for pure alcohol. For the methanol system, it changes from 280 to 55 ps. It is suggested that the process is due to reorientation of two hydroxyl groups in the alcohol chain, which involves breakage and remaking of a hydrogen bond and the low frequency process, of which relaxation time is about 10 ns, is due to reorientation of alcohol molecules bonded to the polymer.

Study on the hydration structure of L‐xylo and D‐arabo ascorbic acid solutions by time domain reflectometry

The hydration structure of L‐xylo and D‐arabo ascorbic acids in aqueous solutions were investigated by a dielectric relaxation measurement over a wide frequency range from 10 MHz to 10 GHz from a standpoint on the difference of biological activity at 25 °C. In order to clarify the hydration structure the concentration dependence of dielectric relaxation was investigated not only in aqueous solution but in water–ethanol mixtures. Two kinds of dielectric relaxation processes were observed in each isomerism solution. The low frequency process is assigned to cooperative motions of ascorbic acid molecules and hydrated water. The high frequency process is assigned to reorientational motions of bulk water. From the results of the dehydration process out of the ascorbic acid surface by ethanol it is concluded that the amount of hydrated water of the L‐xylo ascorbic acid is more than that of the D‐arabo ascorbic acid.