Temperature Dependent Percolation Research Articles

An analytical investigation of self-temperature-compensated stretchable piezoresistive nanocomposites containing hybrid carbon black/carbon nanotube nanofillers

In this study, the temperature-dependent piezoresistivity of hybrid carbon black (CB)/carbon nanotube (CNT) nanocomposites is studied using a percolation model with a Monte Carlo simulation approach. With this approach, the temperature-dependency of electrical resistivity and the strain sensitivity of the nanocomposite are investigated. In addition, other parameters such as the aspect ratio, dispersion state and dimensions’ effect on piezoresistivity of the compensated stretchable nanocomposite are investigated. By developing a temperature-dependent percolation model, the temperature sensitivity response of nanocomposite is investigated based on defining the temperature coefficient of resistance of CNT and thermal expansion coefficient of polymer. It is found that the dimensional aspects and dispersion state affected the percolation threshold and resistivity. The obtained results also indicated that the piezoresistivity increased with the decrease in the Poisson’s ratio and intrinsic electrical conductivity. Moreover, the predicted results showed high prediction accuracy for temperature-dependence resistivity compared with the existing experimental data.

A novel temperature-dependent percolation model for the electrical conductivity and piezoresistive sensitivity of carbon nanotube-filled nanocomposites

Monte Carlo simulation is paired with a percolation model to analytically investigate the temperature effect and carbon nanotube (CNT) dispersion state on the temperature-dependent piezoresistive conductive network nanocomposite. The charge transport switch from electrical tunneling to elevated temperature quantum tunneling is studied based on a temperature-dependent tunneling model. The percolation network theory searches for the shortest distance of any CNT line segments scattered in the representative volume element to form possible interconnections and tunneling resistance approach evaluates resistivity by recognizing the conductive percolating paths. The effect of different factors such as the height of barrier potential, CNT length, degree of orientation and the cutoff distance on the resistance of the nanocomposite which is mainly caused by the inter-tube tunneling resistance is studied through analytical parametric studies. It is shown that the strain sensitivity of reinforced nanocomposite is increased as a result of the uniform dispersion of short aligned CNTs.

Concentration Fluctuation and Salt-Induced Percolation in 1-Propanol Aqueous Solution

Temperature dependent Kirkwood-Buff parameters G p p , G w w and G p w have been evaluated for the 1-propanol-water solution (1:5 in mole ratio) from S c c (0) obtained by small angle neutron scattering (SANS) experiments. Structural model for the concentration fluctuation for the solution at 25°C has been constructed based on the value of G p p . Characteristic feature of the SANS intensity and fractal nature of the concentration fluctuation can be explained qualitatively by the model structure. The volume fraction w of propanol-rich regions in the solution has been estimated as a function of temperature. Salt-induced phase separation phenomena observed on the current solution is discussed based on the temperature-dependent percolation theory.

Irreversibility Lines in Halogen- and Hydrogen-Doped YBa2Cu3O7−δ Compounds

We measure the real and imaginary parts of the ac magnetic permeability of YBa2Cu3O7−δA x (A = Cl, F, H) ceramics and powders as functions of temperature and ac magnetic field amplitude H0, applying uncommonly low and widely ranged excitation fields (1 mOe ≤ Ho ≤ 200 Oe). We determine the temperature dependence of two loss peaks, Hp(T) ∼ (Tc − T)2.7 at low fields in ceramics and Hm(T) ∼ Ts0 − T at higher fields in both powders and ceramics. The extrapolated field Hp(0) and characteristic temperature Tc depend on x and δ, whereas Hm(0) and Ts0 depend mainly on δ. The real part of the permeability indicates a two-step flux-penetration process with two threshold fields for flux penetration. The latter govern the temperature dependence of maxima in the imaginary part as well as the peaks' widths. We propose a field-dependent percolation description of this process, derived from a previous temperature-dependent percolation model. It involves two penetration depths, the classic Ginzburg–Landau one and a low-field abnormally large penetration depth due to chemical disorder. Correspondingly, two types of vortices describe high- and low-field dissipation peaks.

Temperature-Dependent Percolation in the Ordered Phase–Square Lattice-Gas Model–

Critical percolation density for temperature-dependent site percolation problem is calculated by using the lattice-gas model of atoms, especially inside the region where the sublattice ordering occurs (repulsive interaction) or liquid and gas phases coexist (attractive interaction). The square lattice is regarded as a resistor network. Any bond in the lattice is conductive or insulating whether both ends of the bond are occupied with atoms or not. The distribution of atoms is determined within the pair approximation from the lattice-gas Hamiltonian with nearest-neighbor interactions. Moreover a single-site effective-medium approximation which is similar to coherent potential approximation is used to obtain the critical percolation density.

Temperature-Dependent Percolation in the Square Lattice

A single-site effective medium theory is used to study temperature-dependent percolation. The special case discussed is the coraductivity of a lattice gas with nearest-neighbor interactions. The assemblies of atoms are regarded as a square resistor network consisting of randomly distributed conductive bonds, which are assumed to correspond to pairing of atoms. The estimated values of critical percolation-concentration of atoms are proved to be in good agreement with Monte Carlo results.