Oscillations of the electrical resistance induced by shear deformation in molten carbon black composites

Percolation of rigid fractal carbon black aggregates

We examine network formation and percolation of carbon black by means of Monte Carlo simulations and experiments. In the simulation, we model carbon black by rigid aggregates of impenetrable spheres, which we obtain by diffusion-limited aggregation. To determine the input parameters for the simulation, we experimentally characterize the micro-structure and size distribution of carbon black aggregates. We then simulate suspensions of aggregates and determine the percolation threshold as a function of the aggregate size distribution. We observe a quasi-universal relation between the percolation threshold and a weighted average radius of gyration of the aggregate ensemble. Higher order moments of the size distribution do not have an effect on the percolation threshold. We conclude further that the concentration of large carbon black aggregates has a stronger influence on the percolation threshold than the concentration of small aggregates. In the experiment, we disperse the carbon black in a polymer matrix and measure the conductivity of the composite. We successfully test the hypotheses drawn from simulation by comparing composites prepared with the same type of carbon black before and after ball milling, i.e., on changing only the distribution of aggregate sizes in the composites.

TIME AND TEMPERATURE DEPENDENT PIEZORESISTIVE BEHAVIOR OF CONDUCTIVE ELASTOMERIC COMPOSITES

We report about systematic studies on dynamic piezoresistive characteristics of conductive rubber composites. The temporal changes in electrical resistance of flexible electrically conductive rubber composites were simultaneously monitored during dynamic mechanical loading. Thus, influences of physical parameters such as frequency, temperature, strain amplitude, and matrix stiffness were explored in detail, and the mechanisms behind qualitatively discussed. The filler clusters were found to rearrange in the elastomer matrix during dynamic deformation, witnessed by the decrease in electrical resistance over time. Each test parameter had its own specific effect on the piezoresistance response, and the findings offered an understanding on the filler networking inside the solution styrene butadiene rubber matrix from the perspective of the dynamic piezoresistive characteristics. Higher piezoresistive response was observed near the glass transition temperature. We offer a deeper insight into the behavior and temporal changes in corresponding filler clusters during dynamic deformations of conducting rubber systems.

Conductivity and phase morphology of carbon black-filled immiscible polymer blends under creep: an experimental and theoretical study

The simultaneous evolution of conductivity and phase morphology of blend composites was investigated under shear and in the quiescent state.

Molecular dynamics simulation of the conductivity mechanism of nanorod filled polymer nanocomposites

We adopted molecular dynamics simulation to study the conductive property of nanorod-filled polymer nanocomposites by focusing on the effects of the interfacial interaction, aspect ratio of the fillers, external shear field, filler-filler interaction and temperature. The variation of the percolation threshold is anti N-type with increasing interfacial interaction. It decreases with an increase in the aspect ratio. At an intermediate filler-filler interaction, a minimum percolation threshold appears. The percolation threshold decreases to a plateau with temperature. At low interfacial interaction, the effect of an external shear field on the homogeneous probability is negligible; however, the directional probability increases with shear rate. Moreover, the difference in conductivity probabilities is reduced for different interfacial interactions under shear. Under shear, the decrease or increase of conductivity probability depends on the initial dispersion state. However, the steady-state conductivity is independent of the initial state for different interfacial interactions. In particular, the evolution of the conductivity network structure under shear is investigated. In short, this study may provide rational tuning methods to obtain nanorod-filled polymer nanocomposites with high conductivity.

Mapping the electrical conductivity of poly(methyl methacrylate)/carbon black composites prior to and after shear

In this letter, the electrical conductivity of disklike poly(methyl methacrylate)/carbon black composite samples was investigated prior to and after a shear process. Novel electrical conductivity maps of the samples as a function of the position were obtained. It was found that the electrical conductivity after angular averaging of the static (nonsheared) sample is, as expected, independent of the radius. However, for the sheared sample, the electrical conductivity is decreasing from the center to the outer rim of the sample. This is attributed to the interplay of destruction and buildup effects of the applied linear shear stress on the agglomerate network.