Fabrication of well dispersed poly(vinylidene fluoride)/expanded graphite/ionic liquid composites with improved properties by water-assisted mixing extrusion

Poly(vinylidene fluoride)/expanded graphite/ionic liquid (PVDF/EG/IL) composites are fabricated by a one-step melt mixing extrusion especially with water injection. It is found that the IL helps the EG to be exfoliated and dispersed well in the PVDF matrix especially with water injection, which is confirmed by the results of the scanning electron microscopy micrographs and Wide-angle X-ray diffraction. Thus, the PVDF/EG/IL composites especially with water injection exhibit much higher electrical and thermal conductivities than the PVDF/EG composite. The PVDF/EG/IL composite with loading of 4 wt% EG prepared with water injection exhibits electrical conductivity of about 8.9 × 10−9 S/m, which is almost 6 times higher than the one prepared without water injection and 3 orders higher than the PVDF/EG composite. And the enhancements in the thermal conductivities are 107.7% and 132.8% for the PVDF/EG/IL composites prepared without and with water injection, respectively, which are much higher than those of the PVDF/EG composite. Moreover, the introduced IL especially with better dispersion caused by water injection induces the formation of polar crystals due to the ion-dipole interaction between the ammonium ions of the IL and the C–F dipoles of the PVDF chain.