Abstract
The dielectric property and percolated behaviour of polymer matrix composites largely depend on the morphology of conductive fillers and external stimulations especially when the composites are processed by melting blending and extrusion-injection way. In this study, the poly(methyl methacrylate) (PMMA) matrix composites incorporated by two kinds of graphene nanoplatelets (GNP), G5 and G150 with different aspect ratios (the ratio of diameter and thickness) are prepared to study the influence of GNP morphology on the dielectric performances close to percolation threshold (fc). After annealing at glass transition temperature (Tg) for 1 h, the dielectric permittivities of PMMA/G5 and PMMA/G150 near fc increase 43 and 38%, respectively, while the dielectric loss change little. This improvement on the dielectric property is possibly attributed to the slight change of the distance between adjacent GNPs after annealing at Tg which enables to arouse stronger polarisation by tunnelling effect.
Highlights
IntroductionThe percolated behavior is a classical topic when discussing the dielectric property of the composites with conductive fillers since when the volume fraction is approaching to a certain value, known as percolation threshold (fc), the dielectric performance of the composite will change thoroughly.[1, 2] researchers usually take advantages of this percolated transition to achieve the composite for high dielectric properties.[3,4,5,6] Huge amounts of reported studies have shown that various factors influence the percolation behavior of composites and their dielectric properties, [7,8,9] such as the morphology of the filler, the nature of the polymer matrix and processing methods which makes the obtained property hard to duplicate
It is widely accepted that when the polymer is heated to the Tg, the molecule chains start to move due to the expansion of the free volume around. [18, 19] If the composite close to the fc is annealed at the Tg for enough duration, it is highly possible that the dielectric property may be different since the slight change of the free volume around the molecule chains in the interfacial region enables to induce the shrinkage of the distance between adjacent conductive fillers
3.1 Morphology characterization for two kinds of graphene nanoplatlets (GNP) and fractures of their poly(methyl methacrylate) (PMMA) composites As shown in the Fig. 1 (a) and (b), it can be found that the average diameter of G5 is larger than that of G150 while G5’s thickness is thinner than that of G150 by the semi-transparent layer of G5 in the Fig. 1 (a)
Summary
The percolated behavior is a classical topic when discussing the dielectric property of the composites with conductive fillers since when the volume fraction is approaching to a certain value, known as percolation threshold (fc), the dielectric performance of the composite will change thoroughly.[1, 2] researchers usually take advantages of this percolated transition to achieve the composite for high dielectric properties.[3,4,5,6] Huge amounts of reported studies have shown that various factors influence the percolation behavior of composites and their dielectric properties, [7,8,9] such as the morphology of the filler, the nature of the polymer matrix and processing methods which makes the obtained property hard to duplicate. [18, 19] If the composite close to the fc is annealed at the Tg for enough duration, it is highly possible that the dielectric property may be different since the slight change of the free volume around the molecule chains in the interfacial region enables to induce the shrinkage of the distance between adjacent conductive fillers With this suppose, we use poly(methyl methacrylate) (PMMA), a widely used amorphous polymer in the industry as the polymer matrix to prepare the composite. Based on the results of the dynamic mechanical analysis (DMA), the interaction in the interfacial region of GNP and PMMA are analyzed and the effect of thermal treatment on the dielectric properties for the two kinds of PMMA/GNP composites approaching their fc will be well studied
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