石墨烯/聚乙烯醇/聚偏氟乙烯基纳米复合薄膜的介电性能

Dielectric properties of graphene/poly(vinyl alcohol)/poly(vinylidene fluoride) nanocomposites films

石墨烯由于具有良好的力学性能、高的电子传递能力以及相对较低的生产成本等优势而受到广泛关注,但现在多将其直接分散在聚合物中提高聚合物的介电性能.本工作中,制备出了还原氧化石墨烯/PVA/聚偏氟乙烯（PVDF）的三相纳米复合薄膜.首先把聚乙烯醇（PVA）和氧化石墨烯（GO）分散于二甲基亚砜（DMSO）中,得到PVA非共价键修饰的GO,再将PVDF溶于该混合液体中,通过溶液浇注以及低温加热过程得到三相纳米复合薄膜.实验结果表明,在120℃下,GO可以被热还原成还原氧化石墨烯（RGO）,且可以促进PVDF的α相向β相转变.PVA修饰RGO比单纯RGO在PVDF基体中分散性要好,且使PVDF的球晶尺寸大大降低,复合薄膜的介电性能大幅提高.RGO/PVA/PVDF复合膜的渗流阈值fvol^＊约为8.45 vol.%,在10-2Hz时RGO/PVA/PVDF复合膜的介电常数大约是纯PVDF的238倍.本工作为制备介电性能高、生产成本低、操作简单的聚合物纳米复合材料提供了一种好的方法.

Graphene has been a superstar in the fields ranging from materials science to condensed-matter physics since 2004.Graphene possesses good thermal and mechanical properties,high electron transfer capability and relatively low production cost.As a consequence,graphene has been used in the areas of multi-functional advanced materials and electronics.A direct disperse method has been widely applied to polymers to improve their dielectric properties.Recently,graphene/polymer composites have received much attention.Graphene nanosheets can significantly improve the physical properties of the host polymer at a very low content of conductive filler loading.Poly vinylidene fluoride（PVDF）is a semicrystalline thermoplastic polymer with remarkably high piezo-/pyroelectric coefficient,and excellent thermal stability and chemical resistance.More efforts have been recently devoted to the preparations of high-ε′composites based on PVDF.In this work,a graphene/PVA/PVDF nanocomposite film composed of poly（vinyl alcohol）（PVA）,reduced graphene oxide（RGO）,and poly（vinylidene fluoride）（PVDF） is fabricated.First of all,graphene oxide（GO） is prepared by the modified Hummers method.GO and PVA are successively dissolved in the dimethyl sulfoxide（DMSO）solution,in order to obtain PVA functionalized GO which is formed via non-covalent bonds.Then PVDF is added into this solution to form a homogeneous three-phase aqueous mixture.According to the solution-casting and thermal reduction processes,the three-phase nanocomposite films are formed.The thickness values of the films are in a range of 0.3–0.4 mm.The square specimens are coated with a silver paste prior to electrical measurements.The obtained products are characterized using X-ray diffraction,UV Vis absorption spectrum,Fourier transform infrared absorption spectrum,and atomic force microscopy.The morphologies of PVDF and RGO/PVA/PVDF films are investigated by a scanning electron microscope.Electrical measurements are conducted in a frequency range from 10^2 to 10^4Hz.Results suggest that GO can be reduced to RGO and phase transition of PVDF from α to β phases is effectively promoted at120℃.The dielectric properties of the polymer matrix are improved.Furthermore,PVA modified RGO is easier to disperse in the PVDF substrate than the original one,which strongly reduces the spherulite size of PVDF and improves the dielectric property of the composite film.The percolation threshold（fvol^＊） of RGO/PVA/PVDF film is estimated to be 8.45 vol.%,and the dielectric constant of the film is 238 times as large as that of the pure PVDF films at 10^2 Hz.In addition,the dielectric constant increases rapidly near the percolation threshold and depends on frequency,which is mainly ascribed to the Maxwell-Wagner-Sillars polarization in the low frequency range.This study provides a low-cost and simple method of preparing polymer nanocomposites with high dielectric properties.