Conductivity of polymethylmethacrylate filled with carbon black or carbon fibres under oscillatory shear

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.

EFFECT OF THE NANOFILLER SHAPE ON THE CONDUCTIVE NETWORK FORMATION OF POLYMER NANOCOMPOSITES VIA A COARSE-GRAINED SIMULATION

It is very important to improve the electrical conductivity of polymer nanocomposites, which can widen their application. The effect of the nanofiller shape on the relationship between the nanofiller microstructure and the conductive probability of the nanofiller filled polymer nanocomposites (PNCs) has been investigated in detail by employing a coarse-grained molecular dynamics simulation. Four kinds of nanofiller shapes are considered: rod filler, Y filler, X filler, and sphere filler. First, the mean square radius of gyration gradually decreases from rod filler, Y filler, X filler, to sphere filler, which reflects the highest aspect ratio for rod filler. Meanwhile, the dispersion state of the nanofiller is relatively uniform in the matrix. The conductive probability (denoted by the formation probability of the conductive network) is adopted to stand for the conductive property. The results show that the conductive probability gradually decreases from rod filler, Y filler, X filler, to sphere filler, which is attributed to their gradually decreased size. In summary, the nanofiller shape affects the electric conductive property of PNCs.

Comparison study of carbon black (CB) used as conductive filler in epoxy and polymethylmethacrylate (PMMA)

A comparison study between carbon black (CB) filled thermoset (epoxy) and thermoplastic, polymethylmethacrylate (PMMA), was done in this research. CB was introduced as the conductive filler in epoxy and PMMA at different filler loading, which ranged from 5 vol.% to 20 vol.%. The physical, mechanical, electrical and thermal stability properties were investigated. The incorporation of CB into both epoxy and PMMA increased the density, improved the thermal stability and electrical conductivity of the composites, reduced the coefficient of thermal expansion and weakened the flexural and fracture toughness properties of the composites.

Destruction and recovery of a nanorod conductive network in polymer nanocomposites via molecular dynamics simulation

By adopting coarse-grained molecular dynamics simulation, we investigate the effects of end-functionalization and shear flow on the destruction and recovery of a nanorod conductive network in a functionalized polymer matrix. We find that the end-functionalization of polymeric chains can enhance the electrical conductivity of nanorod filled polymer nanocomposites, indicated by the decrease of the percolation threshold. However, there exists an optimal end-functionalization extent to reach the maximum electrical conductivity. In the case of steady shear flow, both homogeneous conductive probability and directional conductive probability perpendicular to the shear direction decrease with the shear rate, while the directional conductive probability parallel to the shear direction increases. Importantly, we develop a semi-empirical equation to describe the change of the homogeneous conductive probability as a function of the shear rate. Meanwhile, we obtain an empirical formula describing the relationship between the anisotropy of the conductive probability and the orientation of the nanorods. In addition, the conductivity stability increases with increasing nanorod volume fraction. During the recovery process of the nanorod conductive network, it can be fitted well by the model combining classical percolation theory and a time-dependent nanorod aggregation kinetic equation. The fitted recovery rate is similar for different nanorod volume fractions. In summary, this work provides some rational rules for fabricating polymer nanocomposites with excellent performance of electrical conductivity.

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.