Dynamics of the conductance temperature dependence for composite based on linear polyethylene with impurity of soot and calcite

Abstract

Within the temperature 293 to 425 K and frequency 10 -3 to 10 6 Hz ranges by using the direct and alternating currents, the dynamics of electrical conductance σ of linear polyethylene with the impurity of 20 wt.% soot and 20 wt.% CaCO 3 (calcite) has been investigated. It has been shown that for the solid state of polyethylene (below 380 K), the dependence of electrical conductance on the temperature T on both the direct (σ DC ) and alternating (σ AC ) currents can be described by the power dependence on ( )is the temperature of the phase transition for polyethylene). It has been shown that when being repeatedly measured, the σ DC and σ AC values increase, and the power indexes of temperature dependence decrease. The measured values are stable after the fourth measurement. The greatest changes in the conductance, depending on the first and second measurements (almost three orders of magnitude), were observed at a temperature close to T 0 . It has been assumed that the dynamics of electrical conductance, depending on the number of measurements, is caused by the influence of the electric field on the ordering of impurity in polymer. It has been shown that for T > 380 K, the typical for liquids Arrhenius dependence of σ DC and σ AC on temperature is observed. It has been found that at the first measurement, the temperature dependence of σ DC and σ AC can be described by two activation energies, while for a stable state (starting from the fourth measurement)by one activation energy (within the measurement error of the same for σ DC and σ AC and equal to 1 eV).

Features of dielectric properties of medical thermal indicators based on dispersions of cholesteric liquid crystals in the polymer matrix

“…Our studies by using an electron microscope at the voltage 20 kV (like that we used in [7]) showed that the diameter of the CLC droplets in the polymer matrix is close to 100 μm. Given that when observing in the visible to the human eye range of the spectrum of electromagnetic waves, the step of the cholesteric helix is close to 1 μm, the following can be stated: in the manufactured dispersions of CLC in the polymer matrix there were no obstacles to the "untwisting" of the cholesteric spiral in droplets, the size of which is much (more than 100 times) larger than the step of the cholesteric spiral.…”

“…Assuming that the equivalent circuit of the measuring cell is a resistor and capacitor connected in parallel, we determined the values of resistance R and capacitance C of the samples at various frequencies, and being based on these values and geometric dimensions of the cell we calculated imaginary (ε") and real (ε') components of the complex dielectric permittivity, respectively. The main results and conclusions of this work will be formulated exactly on the basis of the analysis of the reasons for differences in the frequency dependences of ε' and ε" of dispersions of CLC in the polymer matrix for two types of samples, selective reflection of light in which occurs at the temperatures 36.6 °C and 38.5 °C, as well as comparing these data with the frequency dependences of the dispersions of NLC obtained in [7]. Fig.…”

“…This solution was heated to the temperature close to 40 °C, and carbon black was introduced into it by mechanical stirring, followed by sonication. As in [7], we used N220 carbon black (Kremenchug Plant of Technical Carbon, Ukraine). The concentration of carbon black was 20% with respect to the polymer weight.…”

“…As in [7,8], the dielectric properties of the obtained sandwich samples were investigated within the frequency range 6…10 6 Hz by using the oscilloscopic method [9]. As electrodes, we used glass plates coated with a conductive layer of ITO (mixtures of tin and indium oxides).…”

“…When measuring the dielectric properties of the samples, the amplitude of the measuring signal of the sinusoidal shape was 1.0 V. The amplitude of the measuring signal, which is higher than in [7], could be used due to the fact that electro-optical effects in CLC occur at electric fields higher by more than one order of magnitude than those used in NLC. Assuming that the equivalent circuit of the measuring cell is a resistor and capacitor connected in parallel, we determined the values of resistance R and capacitance C of the samples at various frequencies, and being based on these values and geometric dimensions of the cell we calculated imaginary (ε") and real (ε') components of the complex dielectric permittivity, respectively.…”