This work presents a novel approach to precisely tailor the interfacial layer thicknesses of BaTiO3 by modulating the polymerization degree of a rigid liquid-crystalline fluoro-polymer to investigate the interfacial thickness effect on the dielectric behavior of polymer nanocomposites.
Polymer nanocomposites based on conductive fillers for high performance dielectrics have attracted increasing attention in recent years. However, a number of physical issues are unclear, such as the effect of interfacial thickness on the dielectric properties of the polymer nanocomposites, which limits the enhancement of permittivity. In this research, two core-shell structured reduced graphene oxide (rGO)@rigid-fluoro-polymer conducting fillers with different shell thicknesses are prepared using a surface-initiated reversible-addition-fragmentation chain transfer polymerization method, which are denoted as rGO@PTFMS-1 with a thin shell and rGO@PTFMS-2 with a thick shell. A rigid liquid crystalline fluoride-polymer poly{5-bis[(4-trifluoro-methoxyphenyl)oxycarbonyl]styrene} (PTFMS) is chosen for the first time to tailor the shell thicknesses of rGO via tailoring the degree of polymerization. The effect of interfacial thickness on the dielectric behavior of the P(VDF-TrFE-CTFE) nanocomposites with rGO and modified rGO is studied in detail. The results demonstrate that the percolation threshold of the nanocomposites increased from 0.68 vol% to 1.69 vol% with an increase in shell thickness. Compared to the rGO@PTFMS-1/P(VDF-TrFE-CTFE) composites, the rGO@PTFMS-2/P(VDF-TrFE-CTFE) composites exhibited a higher breakdown strength and a lower dielectric constant, which can be interpreted by interfacial polarization and the micro-capacitor model, resulting from the insulating nature of the rigid-polymer shell and the change of rGO's morphology. The findings provide an innovative approach to tailor dielectric composites, and promote a deeper understanding of the influence of interfacial region thickness on the dielectric performance.
Dielectric polymer-based nanocomposites have attracted significant attention in recent years for energy storage applications because of their potential high permittivity and breakdown strength. The coupling effect of a nanofiller/matrix interface plays a crucial role in the dielectric and electric properties of polymer-based nanocomposites. In this paper, three kinds of side-chain liquid crystalline fluoric-polymers, denoted as P-nF (n = 3, 5 or 7, which is the number of terminal fluoric groups), were grafted on the surface of BaTiO3 nanoparticles by a surface-initiated reversible-addition-fragmentation chain transfer polymerization method. The nanocomposite films were prepared via core-shell BaTiO3 nanoparticles dispersed in a poly(vinylidene fluoride-trifluoroethylene-chlorotrifluoroethylene) P(VDF-TrFE-CTFE) polymer matrix. The frequency dependent dielectric properties and energy storage capability of the polymer nanocomposites were studied. The results showed that the permittivity and energy densities of the polymer nanocomposites depended on the molecular structure of the modifier, especially the number of electron-rich fluoric groups. Firstly, all modified BaTiO3 nanoparticles were homogeneously dispersed in the polymer matrix, resulting in the polymer nanocomposites presenting a higher breakdown strength compared with the unmodified BaTiO3 nanoparticles. Secondly, the changes in the nanocomposites' permittivity exhibited diversity for three modifiers due to many influential factors. Thirdly, compared with neat P(VDF-TrFE-CTFE), the discharge energy densities of the polymer nanocomposites are all significantly improved. The highest discharge energy densities of nanocomposites with 5 vol% P-3F@BT reached 14.5 J cm-3. These findings suggest that the optimal interfacial modifier should be carefully decided by combining various properties of the nanocomposites for energy storage.
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