The breakup of the rubber phase in an ethylene–propylene–diene monomer (EPDM)/polypropylene (PP) blend at the early stage of dynamic vulcanization is similar to that in an unvulcanized EPDM/PP blend because of the low crosslink density of the EPDM phase. In this work, the minimum size of the rubber phase in the unvulcanized EPDM/PP blend was first calculated by using the critical breakup law of viscoelastic droplets in a matrix. The calculated results showed that the minimum size of the rubber phase in the unvulcanized blend was in the nanometer scale (25–46 nm), not the micrometer scale as reported in many works. Meanwhile, the actual size of the rubber phase in the thermoplastic vulcanizate (TPV) at both the early stage and the final stage of dynamic vulcanization was observed by using peak force tapping atomic force microscopy (PF-AFM). The results indicated that the EPDM phase indeed broke up into nanoparticles at the early stage of dynamic vulcanization, in good agreement with the calculated results. More interestingly, we first revealed that the micrometer-sized rubber particles commonly observed in TPV were actually the agglomerates of rubber nanoparticles with diameters between 40 and 60 nm. The mechanism for the formation of rubber nanoparticles and their agglomerates during dynamic vulcanization was then discussed. Our work provides guidance to control the microstructure of the rubber phase in TPV to prepare high performance TPV products for a wide range of applications in the automobile and electronic industries.

A novel dielectric composite with high dielectric constant (k), low dielectric loss, low elastic modulus and large actuated strain at a low electric field was prepared by a simple, low-cost and efficient method. The graphene oxide nanosheet (GO)-encapsulated carbon nanosphere (GO@CNS) hybrids were fabricated for the first time via π–π interaction and hydrogen bonding interaction by simply mixing the CNS and GO suspension. The assembly of GO@CNS hybrids around rubber latex particles was realized by hydrogen bonding interaction between carboxylated nitrile rubber (XNBR) and GO@CNS hybrids during latex compounding. The thermally reduced GO (RGO)@CNS/XNBR composites were then obtained from GO@CNS/XNBR by vulcanization and in situ thermal reduction, resulting in the formation of a segregated filler network. The results showed that k at 10³ Hz obviously increased from 28 for pure XNBR to 400 for the composite with 0.75 vol% of the hybrids because of the formation of a segregated filler network and the increased interfacial polarization ability of the hybrids after in situ partial thermal reduction. Meanwhile, the composite with 0.75 vol% of the hybrids retained low conductivity (10⁻⁷ S m⁻¹), resulting in low dielectric loss (<0.65 at 10³ Hz). In addition, the elastic modulus only mildly increased with the addition of 0.75 vol% of the hybrids, retaining the good flexibility of the composites. More interestingly, the actuated strain at 7 kV mm⁻¹ obviously increased from 2.69% for pure XNBR to 5.68% for the composite with 0.5 vol% of RGO@CNS, and the actuated strain at a lower electric field (2 kV mm⁻¹) largely increased from 0.23% for pure XNBR to 3.06% for the composite with 0.75 vol% of RGO@CNS, which is much higher than that of other dielectric elastomers reported in previous studies, facilitating the application of the dielectric elastomer in biological and medical fields, where a low electric field is required.