Preparation And Properties Of Polymer-Based Graphene Dielectric Composites

Dielectric materials have the characteristics of energy storage and average electric field,which are the research hot spots in recent years.Polymer is the preferred material for the development of small and lightweight dielectric materials because of its low density,excellent electrical insulation,processability and mechanical properties.Graphene has high conductivity,strength and specific surface areas,and the dielectric constant of the polymer can be significantly increased by adding small loading of graphene,showing a broad application prospect in biological medicine,capacitors,wave-absorbing materials and so on.In this paper,the preparation process of reduced graphene oxide(rGO)was optimized first,and then polyvinylidene fluoride(PVDF)/rGO and polystyrene microspheres(PSt)/rGO composites were prepared respectively.The morphology and structure of the products were characterized by FT-IR,XRD,Zeta potentiometer,SEM and TEM,and the effect of rGO content on the properties of the composites was studied.Graphene oxide(GO)was prepared by improved Hummers method.Extending the time of medium temperature oxidation and using ultrasonic treatment were beneficial to the oxidation and peeling of graphite so as to obtain the flaky GO.Three reduction methods including hydrazine hydrate,high temperature and alkali treatment at low temperature could reduce GO to rGO,thereinto hydrazine hydrate was most effective.PVDF/rGO composites were prepared by solution mixing of GO with PVDF and the subsequent hot pressing.Results showed that rGO dispersed uniformly in PVDF matrix at small rGO loading,while agglomerated with rGO loading increased.When the content of rGO increased from 0 wt%to 8 wt%,the dielectric constant(ε_r)of PVDF/rGO composites increased from 6.6 to 38.6 at20℃,100 Hz,the dielectric loss(tanδ)was also slightly rising.The tensile strength and thermal stability of the composites increased firstly and then decreased.Compared with the pure PVDF,the tensile strength of composites containing 4 wt%rGO increased by 35.3%and reached the maximum value of36.19 MPa,and the decomposition temperature of 5 wt%weight loss was 6.44℃higher.Moreover,the breaking elongation and the breakdown strength of the composites decreased with the addition of rGO.PSt/rGO composites were prepared by mixing of GO with PSt latex particles and following hydrazine hydrate reduction.Results demonstrated that rGO dispersed in the PSt matrix uniformly.The conductive network gradually formed with the addition of rGO,andε_r as well as tanδof the composites increased sharply.The characteristic breakdown strength of the composites increased firstly and then decreased with the addition of rGO,and reached the maximum value of53.44 KV/mm at 0.5 wt%rGO,which was 80.9%higher than that of pure PSt.Meanwhile,the addition of rGO increased the thermal stability of the composites.In PSt/rGO(5 wt%rGO)composites,the decomposition temperature of 5 wt%weight loss was 34.04℃higher than that of pure PSt microspheres.