The electrical conductivity of poly(ethy1ene oxide) of different molecular weights in 0.1 M KCl electrolyte solution has been measured in the temperature interval from 0 to 55 "C. The data have been interpreted on the basis of the Looyenga equation for heterogeneous systems, found to apply with good approximation also for other transport properties. The hydration number deduced from these measurements has been estimated to be lower than that reported elsewhere. Its dependence on temperature, however, supports the occurrence of a cloud point temperature which agrees with the values observed in similar systems. These findings are consistent with the measured activation enthalpy values, which are very similar to that of the pure solvent, indicating that poly(ethy1ene oxide)-water interactions give rise to a structure that would form a rather open hydrogen-bonded network.

The permittivity and dielectric loss of an acetamide-sodium thiocyanate mixture have been measured over a wide frequency interval, from lo-' to 10' Hz. The observed dielectric dispersions have been interpreted on the basis of a polymeric model previously proposed. The dipole moment of the acetamide molecule as a function of temperature and the displacement and mobility of solvated Na+ ion have been estimated.

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The influence of the cell shape on the dielectric and conductometric properties of biological cell suspensions has been investigated from a theoretical point of view presenting an analytical solution of the electrostatic problem in the case of prolate and oblate spheroidal geometries. The model, which extends to spheroidal geometries the approach developed by other researchers in the case of a spherical geometry, takes explicitly into account the charge distributions at the cell membrane interfaces. The presence of these charge distributions, which govern the trans-membrane potential DeltaV, produces composite dielectric spectra with two contiguous relaxation processes, known as the alpha-dispersion and the beta-dispersion. By using this approach, we present a series of dielectric spectra for different values of the different electrical parameters (the permittivity epsilon and the electrical conductivity sigma, together with the surface conductivity gamma due to the surface charge distribution) that define the whole behavior of the system. In particular, we analyze the interplay between the parameters governing the alpha-dispersion and those influencing the beta-dispersion. Even if these relaxation processes generally occur in well-separated frequency ranges, it is worth noting that, for certain values of the membrane conductivity, the high-frequency dispersion attributed to the Maxwell-Wagner effect is influenced not only by the bulk electrical parameters of the different adjacent media, but also by the surface conductivity at the two membrane interfaces.

The effect of shape on the dielectric and conductometric spectra of aqueous suspensions of non-spheroidal biological cells has been investigated by means of numerical simulation methods. This work extends our previous investigation directed to biological cell systems where a superficial electric charge distribution is present on the outer interface of the cell membrane. This generalization results in a more composite dielectric spectra, where a low-frequency and a high-frequency contribution are expected. We consider different geometries, from ellipsoids, discoids, pear-shaped vesicles, cup-shaped vesicles to budded vesicles, which model a biological cell during different processes of biological relevance. The overview of the evolution of the dielectric spectra with the progressive change in the cell shape, maintaining constant the electrical properties of the different media involved and the fractional volume of the dispersed cells, offers a preliminary opportunity to separate contributions derived exclusively from the geometry to those due to the bulk and/or interface polarizations. These aspects are particularly relevant since dielectric spectroscopy of biological cell suspensions has proved its effectiveness in the characterization of the passive electrical properties of the cell membrane and also in controlled manipulations of biological systems.