Electroosmosis and Electric Conduction of Electrolyte Solutions in Charge-Regulating Fibrous Media

An analytical study of the electroosmosis and electric conduction of electrolyte solutions in a fibrous medium composed of parallel charge-regulating cylinders with arbitrary electric double layer thickness is presented. A linearized charge regulation model was adopted for the association and dissociation reactions occurring at the amphoteric functional groups over the surfaces of the cylinders, and a unit cell model was employed to accommodate interactions among the cylinders. The electrokinetic equations governing the ionic concentration, electric potential, and liquid flow fields were solved at low zeta potential for the cylinders. Explicit formulas for the electroosmotic mobility and effective electric conductivity in the fiber matrix were obtained. The results indicate that the charge regulation characteristics, such as the equilibrium constants of the reactions occurring at the cylinders’ surfaces and the bulk concentration of the charge-determining ions, influence the surface charge density and potential, electroosmotic mobility, and effective electric conductivity substantially.

ANALIZA CONDUCTIVITĂȚII ELECTRICE A NANOCOMPOZITELOR PVC-TiO2 PRIN SPECTROSCOPIE DIELECTRICĂ

Electrical conductivity of polyvinyl chloride (PVC) and of PVC-TiO2 nanocomposites with TiO2 nanoparticle concentration of 5% was analyzed by dielectric spectroscopy in the frequency range 10^-2 – 10^6 Hz, and for three different temperatures: 310, 320 and 340 K. Frequency variation of the imaginary part of the complex permittivity was analyzed with Havriliak-Negami (HN) model. Temperature influence on this variation was used to determine the activation energy of electric conduction in the studied materials. Frequency variation of the real part of the complex permittivity was analyzed, as well, and the temperature influence on DC conductivity (σDC) and AC conductivity (σAC) was discussed in the paper. The obtained results emphasize an important temperature influence on the dielectric response and, consequently, on the electrical conductivity, especially at low frequencies up to 10^2 Hz, for both PVC and PVC-TiO2 nanocomposites. Thus, at low frequencies in the range 10^-2 – 10^2 Hz, high frequency variations of the imaginary part of the complex permittivity can be noticed, which indicate important charge movements through the polymeric material under electric field. The increase of the temperature leads to an increase of the DC conductivity values, and to an increase of the frequency threshold up to which a frequency independent electrical conduction can be observed. The study presented in this paper shows that the dielectric spectroscopy is a performant tool that allows, besides the highlighting of dielectric relaxations corresponding to the different polarization types from polymeric materials, also to characterize these materials from the point of view of electric conduction. Thus, by dielectric spectroscopy, the electrical insulating materials from the insulations of power cables and electrical machines can be analyzed in a large range of frequencies and temperatures, which allows the understanding of the behavior of these materials in different operating conditions.

Dispersion Waves in a Submerged Thermo-Piezoelectric Membrane

Wave propagation in a thermo piezoelectric membrane immersed in an infinite fluid medium is discussed using three-dimensional linear theory of elasticity and thermos piezoelectricity. Three displacement potential functions are introduced to uncouple the equations of motion, heat and electric conduction equations. The frequency equations are obtained for longitudinal and flexural modes at the solid fluid interfacial boundary conditions. The numerical results are analyzed for PZT-4 material and the computed stress, strain, electric displacement and temperature distribution are presented in the form of dispersion curves and its characteristics are studied.

Effect of nano and micro conductive materials on conductive properties of carbon fiber reinforced concrete

In this study, the pressure sensitivity and temperature sensitivity of the diphasic electric conduction concrete were investigated by measuring the resistivity using the four-electrode method. The diphasic electric conduction concrete was obtained by mixing nano and micro conductive materials (carbon nanofibers, nano carbon black and steel slag powder) into the carbon fiber reinforced concrete (CFRC). The results indicated that, with the increase of conduction time, the resistivity of CFRC decreased slightly at the initial stage and then became steady, while the resistivity of CFRC containing nano carbon black had a sharp decrease at the dosage of 0.6%. With the increase of compression load, the coefficient of resistivity variation of CFRC containing nano carbon black and steel slag powder changed little. The coefficient of resistivity variation increased with the increase of steel slag powder in the dry environment, and CFRC had preferable pressure sensitivity when the mass fractions of carbon fiber and carbon nanofiber were 0.4% and 0.6%, respectively. Besides, in the humid environment, the coefficient of resistivity variation decreased with the increase of steel slag powder, and the diphasic electric conduction concrete containing 0.4% carbon fibers and 20% steel slag powder had the best pressure sensitivity under the damp environment. Moreover, in the dry environment, CFRC containing nano and micro conductive materials presented better temperature sensitivity in the heating stage than in the cooling stage no matter carbon nanofiber, nano carbon black or steel slag powder was used, especially for the CFRC containing steel slag powder.