Preparation of poly(vinylidene fluoride) films with excellent electric property, improved dielectric property and dominant polar crystalline forms by adding a quaternary phosphorus salt functionalized graphene

In our work, a novel modifier, quaternary phosphorus salt, (1-hexadecyl) triphenylphosphonium bromide (HTPB), was introduced for the noncovalent functionalization of graphene for the first time. With it, an excellent dispersion of graphene in organic solvent and later in poly(vinylidene fluoride) (PVDF) matrix has been achieved, e.g., transmission electron microscopy (TEM) shows a single-layer dispersion and multi-layer structure of graphene sheets in PVDF matrix. As a result, the films exhibit outstanding electric property with a very low percolation threshold of 0.662 wt% being observed. Their dielectric property is also improved, the dielectric constant of PVDF/graphene composites at 1000 Hz with a loading lower than 0.86 wt% shows an obvious increase (more than 3 times of that of PVDF at most), while the dielectric loss remain quite low (all lower than 0.07). Even more intriguingly, the quaternary phosphorus salt also induces dominant polar β and γ crystalline forms in the prepared composite films. These PVDF/graphene films with good electric and dielectric property as well as dominant polar β and γ forms promise a wide range of potential applications in electronic devices.