▎ 摘　　要

In this research, hydroxylated and carboxylated graphene (GROH and GRCOOH) with controllable functionalized level by means of diazonium addition was successfully prepared, and the dielectric properties of polyvinylidene fluoride (PVDF) composites fabricated via a simple solution-cast and hot pressing method are examined. Tunable dielectric properties, low percolation threshold (020 wt%) and large energy density (up to 17.33 J cm(-3) of GROH-50) in the polymeric composites of PVDF/GROH and PVDF/GRCOOH suggests strong chemical bonding are formed between the filler and polymer matrix. Hydroxyl groups, which act as an electron donor, is believed to improve the dielectric properties when compared to carboxyl groups with electron accepting nature, thus GROH/PVDF presents better dielectric behavior (not only high dielectric constant, but also low dielectric loss) than GRCOOH/PVDF. Such polymer composites consisted of functionalized graphene can be used to store charge and electrical energy and play a key role in modern electronics and electric power systems. (C) 2017 Elsevier Ltd. All rights reserved.