Creating molecular bridges across the interfaces in segregated composites toward improved conductive and mechanical properties

Constructing segregated structure in polymer composites is a particularly effective strategy to improve electrical conductivity by selectively distributing fillers in the interstitial space among isolated polymer domains. However, the segregated composites generally suffer from inferior mechanical properties because the fillers at the interfaces hinder chain diffusion and leads to weak interfacial adherence or defects. In this contribution, we present a facile method to fabricate segregated composites with improved electrical conductivities and mechanical properties by creating molecular bridges across the interfaces among the segregated domains. Specifically, β-hydroxyl ester-crosslinked epoxidized natural rubber (ENR) granules were compounded with the master batch of carboxylated nitrile rubber (xNBR) and carbon nanotubes (CNTs), followed by compression molding. In the resultant composites, CNTs embedded in xNBR phase are distributed along the boundaries of ENR domains, and xNBR can act as binder to bridge the crosslinked ENR granules through the reaction of carboxyl groups with the epoxy groups and β-hydroxyl esters on ENR granule surfaces. As a consequence, the segregated composites exhibit greatly improved electrical conductivity and mechanical properties when comparing to their randomly dispersed counterparts. In addition, the segregated network is able to endure deformations and heal damage without significant loss of the electrical conductivity. The conductive and mechanical properties of the composites are found to be closely related to the morphologies of segregated structure and CNT concentration in the continuous xNBR phase.