Naokazu Koizumi

Dielectric Approach to Suspensions of Ellipsoidal Particles Covered with a Shell in Particular Reference to Biological Cells

A dielectric theory of interfacial polarization is presented for a heterogeneous system containing ellipsoidal particles covered with shells, in order to make an analysis of dielectric behavior of suspensions of ellipsoidal biological cells. For the case of spheroidal shapes, dielectric dispersion curves are calculated numerically by using the electrical and morphological parameters relevant to biological cells. The results indicate that the calculated dielectric dispersion curves are seriously affected by varying the axial ratio of the spheroids. For the purpose of analyzing dielectric data of biological cell suspensions on the basis of the presented theory, a procedure is proposed to evaluate electrical parameters characteristic of biological cells. This procedure is shown to be successfully applied to the observed dielectric data of erythrocyte suspensions.

Dielectric properties of yeast cells

SummaryDielectric measurements were made on suspensions of intact yeast cells over a frequency range of 10 kHz to 100 MHz. The suspensions showed typical dielectric dispersions, which are considered to be caused by the presence of cytoplasmic membranes with sufficiently low conductivity. Since the conductivity of the cell wall was found to be of nearly the same value as that of the suspending medium, composed of KCl solutions in a range from 10 to 80mm, the cell wall may be ignored in establishing an electrical model of the cells suspended in such media. An analysis of the dielectric data was carried out by use of Pauly and Schwans theory. The membrane capacitance was estimated to be 1.1±0.1 μF/cm2, which is compared with values reported so far for most biological membranes. The conductivity of the cell interior was almost unchanged with varying KCl concentrations and showed low values owing to the presence of less conducting particles, presumably intracellular organelles. The relatively low dielectric constant of about 50 obtained for the cell interior, in comparison with values of aqueous solutions, may be attributed also to the presence of intracellular organelles and proteins.

Dielectric behavior and ferroelectric transition of copolymers of vinylidene fluoride and trifluoroethylene

Abstract Dielectric behavior of copolymers of vinylidene fluoride (VDF) and trifluoroethylene (TrFE) with VDF contents of 52 to 78 mol % has been investigated over wide frequency and temperature ranges with particular reference to the ferroelectric transition. Some related physical properties such as the dynamic tensile modulus, the thermal expansion, and the enthalpy of transition were also studied. The copolymers exhibited three dielectric relaxations γ, β, and Tt in the increasing order of temperature. The γ process is the local mode relaxation of part of frozen molecular chains below the glass transition. The β relaxation is related with micro-Brownian motions of molecular chain backbone in amorphous regions. The Tt relaxation which is featured with a rather narrow distribution of relaxation times is associated with cooperative motions of molecular chain in crystalline regions in the vicinity of the ferroelectric transition. Dielectric measurements under hydrostatic pressure revealed that the anomalou...

Dielectric properties of emulsions

SummaryDielectric constants of O/W emulsions were measured over a wide range of concentration and at frequencies ranging from 20 cps. to 3 mc.No dielectric dispersion due to the interfacial polarization was observed in the experimental range of frequency, while the electrode polarization was observed below 100 kc.Experimental results were compared with theoretical values for spherical dispersions. It was concluded that the dielectric constants of O/W emulsions were expressed best byBruggemans equation over the whole range of concentration.ZusammenfassungDie DK von öl/Wasser-Emulsionen wurden über einen weiten Konzentrationsbereich und für Frequenzen zwischen 20 Hz und 3 MHz gemessen. Es war keine dielektrische Dispersion verursacht durch OberflÄchenpolarisation innerhalb des experimentellen Frequenzbereiches zu beobachten. Dagegen wurde unterhalb 100 kHz Elektrodenpolarisation bemerkbar.Die experimentellen Ergebnisse wurden mit den theoretischen Darstellungen der Misch-DK für Dispersionen mit kugligen Teilchen verglichen. Der Verlauf der DK der öl/Wasser-Emulsion wird am besten und über den ganzen Konzentrationsbereich durch die Gleichung vonBruggeman dargestellt.

Analysis of dielectric relaxations of w/o emulsions in the light of theories of interfacial polarization

An attempt is made to apply dielectric theories of interfacial polarization to observations of dielectric relaxations for W/O emulsions. Approximate formulas for disperse systems in a W/O type were derived from the two theories: one proposed by Maxwell and Wagner for dilute disperse systems of spherical particles, and the other developed by Hanai for concentrated disperse systems. Dielectric measurements were carried out on concentrated W/O emulsions prepared from kerosene and distilled water or KCl aqueous solutions by minimal use of emulsifiers. Marked dielectric relaxations were observed with the emulsions, the dielectric parameters having been determined to characterize the relaxation data. Phase parameters such as relative permittivity, electric conductivity and volume fraction of the disperse phase were evaluated from the dielectric parameters by use of the approximate formulas of the respective theories. The phase parameters evaluated and the frequency dependence of complex permittivity of the W/O emulsions deduced from the theory for concentrated disperse systems are in excellent agreement with the observed data in comparison to that for dilute disperse systems. It is concluded that the dielectric relaxations due to the interfacial polarization of disperse systems of spheres are explained satisfactorily by the theory for concentrated disperse systems.

A method for determining the dielectric constant and the conductivity of membrane-bounded particles of biological relevance

Numerical assessment is made regarding Pauly and Schwans theory which describes the dielectric behaviour of a suspension of “shell spheres” as a model of biological membrane-bounded particles. The results indicate that approximate expressions of the theory may give rise to serious errors when applied to particles smaller than about 1 Μm in diameter. With a view to performing analysis according to a general expression of the theory, some of the characteristic responses of dielectric parameters upon changes in phase parameters are examined with particular reference to some numerical ranges of biological interest. On this basis a simplified and systematic procedure is proposed for estimating the phase parameters of particles whose shell phase can be regarded as non-conductive. As the application of the procedure proposed, a set of dielectric data of a synaptosome suspension is analyzed, so that the following three phase parameters are successfully determined: membrane capacitance (or shell phase dielectric constant), internal phase conductivity and internal phase dielectric constant. Some limitations of the procedure are discussed for the cases of conducting shells and small particles.

Dielectric properties of yeast cells: Effect of some ionic detergents on the plasma membranes

SummaryDielectric measurements were made on suspensions of yeast cells treated with two homologous series of sodium alkyl (C8, C10, C12, C14) sulfonates and alkyl (C8, C10, C12, C14, C16, C18) benzyl dimethyl ammonium chlorides over a frequency range of 10 kHz to 100 MHz. Dielectric dispersions observed for the suspensions of intact yeast cells are found to be reduced by treatment with these detergents, the reduction being accompanied by a decrease in packed volume of the cells and by a leakage of intracellular compounds. The reduction of dielectric dispersions is considered to be caused by a decrease in volume of the cells in suspensions and an increase in conductivity of the cell membranes. An effect of the alkyl chain length of the detergents on the reduction of dielectric dispersions is also examined for these ionic detergents. The reducing effect shows the maximum at the alkyl chain, C14 for sodium alkyl sulfonates and at C16 for alkyl benzyl dimethyl ammonium chlorides. These results are consistent with hemolysis and bactericidal activity.

Dielectric observations on polystyrene microcapsules and the theoretical analysis with reference to interfacial polarization

Dielectric measurements were carried out for polystyrene microcapsules which were prepared by means of an interfacial polymer deposition technique. The microcapsules showed a couple of dielectric relaxations termedP for lower andQ for higher frequencies. The frequency profiles were characteristic of the structure that shelled spheres were dispersed in a continuous medium. Gelatin aqueous solutions, cationic polyelectrolyte solutions and distilled water were loaded in the capsule interior to examine the effect of conductivities of the constituent aqueous phases on the dielectric properties. Relaxation frequencies of the relaxationsP andQ observed were directly proportional to the conductivities of the continuous medium and of the capsule interior, respectively. A dielectric theory was proposed for a suspension of shelled spheres in a continuous phase in order to analyze the relaxation data observed for the microcapsules. Volume fraction of the capsules, relative permittivity and conductivity of the capsule interior and thickness of the capsule wall are evaluated from the dielectric observations by use of the theoretical formulas derived. The dielectric behavior observed for the polystyrene microcapsules are interpreted quantitatively in terms of the dielectric theory proposed.

Ferroelectric Properties in Polyamides of m-Xylylenediamine and Dicarboxylic Acids

The relationship between electric displacement D and electric field E was studied for polyamides consisting of m-xylylenediamine and aliphatic dicarboxylic acids with numbers of carbon atoms from 6 to 11 and 13. Regardless of the number of carbon atoms in the acids, quenched samples of these polyamides exhibit a D-E hysteresis loop with remanent polarization of 23-67 mCm-2. Polarization is related to the amide groups aligned by the electric field.

Dielectric Hysteresis Loop in Alicyclic and Aromatic Polyamides

The relationship between electric displacement D and electric field E was studied for alicyclic polyamides of 1,3-bis(aminomethyl)cyclohexane and adipic, pimelic and sebacic acids, an aromatic polyamide prepared from hexamethylenediamine (HMD) and isophthalic acid and a copolyamide of HMD with isophthalic and terephthalic acids. Quenched samples of these polyamides were poorly crystalline or amorphous and exhibited a D-E hysteresis loop with the remanent polarization of 26 to 38 mCm-2. The remanent polarizations disappeared at the glass transition temperature of each sample. The origin of the D-E hysteresis loop is attributable to amide groups in amorphous regions.