Non-monotonic dependence of the conductivity of carbon nanotube-filled elastomers subjected to uniaxial compression/decompression

Abstract

Electrical resistance of the elastomeric material polychloroprene filled with multiwalled carbon nanotubes (CNTs) dispersed by using an imidazolium based ionic liquid has been measured experimentally and calculated theoretically, as a function of the applied compression/decompression force F. Both experimental and theoretical results show that the electrical resistance R of the composite exhibits non-monotonic dependence on F. This observed non-monotonic dependence R(F) is explained by different mechanisms of conductivity that are specific to the respective domains of the magnitude of the compression/decompression force F. At small F, the observed decrease of conductivity with increasing F is found to be caused by the change of an average contact distance between CNTs. At higher F, the observed increase of R with increasing F is caused by the dependence of the per-particle surface area on F. The experimentally observed dependence R(F) is adequately described by the developed theory that relies on establishing the exact relation between the CNT network structure and the electrical response of the composite. Theoretical dependence between the conductivity of the composite and the applied stress is obtained using the percolation model of the electrical conductivity of CNT network that shows excellent quantitative agreement with the experimental results.

Conductivity of Insulating Diblock Copolymer System Filled with Conductive Particles Having Different Affinities for Dissimilar Copolymer Blocks

“…To evaluate the conductivity of the composite modeled by the above lattice system, one needs to evaluate the resistance (conductance) of a pair of filler particles that are in contact. In realistic polymer-particle composites, this conductance can be caused [13,14] by unconventional physical mechanisms, such as constriction and hopping conductivity, not restricted to the standard contact conductivity. Because of physical diversity of possible conductivity mechanisms that can vary for different polymer-particle systems, as well as low experimental accessibility of the conductivity of nanoscopic particles, we chose different route for practical evaluation of the composite conductivity.…”

“…The main advantage of a soft polymer matrix as a host system for fillers relative to its hard counterpart is that this matrix can be easily adjusted to required conditions by changing its shape and volume. In particular, host soft polymer matrix has high responsiveness to external stimuli such as shear and stress, which opens a route towards sensing applications [13,14].…”

“…This insulating effect is used to induce the conductor-insulator transition that occurs when the fraction of conductive fillers in a composite reaches a certain percolation threshold. This threshold can be shifted [2,3,13,14] by applying stress to a polymer-particle composite that causes restructuring the conductive filler network formed in this composite. This restructuring results, in turn, in switching among conductivity mechanisms (e.g., constriction and hoping) and changing overall conductivity of the composites in a wide range [13].…”

“…The above described previous work relies on affecting the electrical response of composites by indirectly modifying the distribution of fillers in this composite. A desirable density structure of fillers inside a composite is produced by changing physical structure of this composite through applying external stimuli such as permanent of periodic mechanical load (stress) [13,14] or shear [19]. In the present work we explore a qualitatively different route to governing the conductivity of polymer-particle composites by changing the compositional structure of a host polymer system.…”

Conductivity of diblock copolymer system filled with conducting nano‐particles: Effect of copolymer morphology

“…The described phase transformations can be easily induced by external stimuli (e.g., temperature or pressure) at lowenergetic cost. This feature is superior to the other known ways to achieve restructuring of a filler system immersed in a soft composite, such as stretching a host polymer system [22][23][24][25] or applying a shear. 20,26 Note that the latter method proves [27][28][29] to be effective for lowering the percolation threshold in the system of conducting carbon nanotubes (CNT) immersed in a homopolymer melt.…”