Hierarchical interfaces induce high dielectric permittivity in nanocomposites containing TiO₂@BaTiO₃ nanofibers

Abstract

Interface issues are common and crucial in nanocomposites or nanohybrid systems since the interface area is enormous on the nanoscale. In the 0-3 dimensional polymer nanocomposites, in which nano-inclusions (0-dimension) are embedded in a 3-dimensionally connected polymer matrix, enhanced dielectric permittivity could be induced by the interfacial polarization at the interfaces between the nano-inclusions and the polymer matrix. In this contribution, we propose and demonstrate that the topological structure of the interface plays an equally important role as the area of the interface in determining the dielectric polarization of polymer nanocomposites. TiO2 nanofibers embedded with BaTiO3 nanoparticles are prepared via electrospinning and then fused with polyvinyl difluoride (PVDF) into polymer nanocomposite films. Modulation of hierarchical interfaces is thus achieved for these nanocomposites. The confinement of these additional interfaces inside the TiO2 nanofibers leads to percolated networks formed by the interfacial regions. The dielectric permittivity of the polymer nanocomposites is thus enhanced by ∼300% over the PVDF matrix at a low filler loading of 11 vol%. A phase-field simulation study indicates that the enhanced dielectric permittivity could be attributed to the increased polarization in the percolated interfacial regions inside the TiO2 nanofibers. The instantaneous electrical breakdown of the TiO2@BaTiO3 nanofibers studied by the in situ transmission electron microscopy method further reveals the striking feature that the breakdown behavior of the nanofibers changes from semiconductive to metallic with the incorporation of insulating BaTiO3 nanoparticles.

Ultrahigh Energy Density of Polymer Nanocomposites Containing BaTiO3@TiO2 Nanofibers by Atomic‐Scale Interface Engineering

“…The percolation of the TiO 2 /BaTiO 3 interfaces gives rise to much enhanced interfacial polarization of the BTO@TO_nfs, leading to substantially increased ε r of the polymer nanocomposites (>41) at a rather low volume fraction of ≈10 vol%. [ 18 ] More importantly, improved E B (≈650 kV mm -1 ) is also achieved by taking advantage of the large aspect ratio of the nanofi bers, which is even higher than that of the pristine PVDF matrix. These very favorable features give rise to an ultrahigh energy density of ≈20 J cm -3 .…”

“…An in situ observation of electric breakdown of the TO@BTO_nfs by TEM further confi rms that the electric breakdown characteristics of the BTO@TO_nfs change from being insulating to more conductive behavior with percolating interfacial regions. [ 18 ] Indeed, atomic-scale structural characterization reveals that an interfacial region about 2 nm exists around each BaTiO 3 particle embedded in the TiO 2 nanofi bers. Figure 4 a provides the simulated angular bright-fi eld (ABF) images of BaTiO 3 and TiO 2 , from which we should notice that there is no contrast between two Ba atoms in BaTiO 3 while there always exists a dark contrast between two relative dark contrast in TiO 2 along the horizontal direction.…”

Improved dielectric permittivity and retained low loss in layer-structured films via controlling interfaces

“…However, the dielectric permittivities of polymer dielectrics are usually very low (below 10 @1 kHz), which greatly hindered their wide applications. Toward this end, two strategies have been developed to improve the dielectric constants of polymer composites: (1) ceramic-polymer composites composed of high-k ceramic fillers (e.g., BaTiO 3 [23][24][25][26][27], TiO 2 [28,29], SrTiO 3 [30]) dispersed in polymer matrix and (2) conductor-polymer composites consisting of conductors (e.g., metals, [31,32], graphite [33,34], carbon nanotube [35][36][37], graphene [38,39], carbon black [40], and conductive polymer [41,42]) dispersed in polymer matrix. For ceramic-polymer composites, the enhancement of permittivity is limited (below 50 @10 kHz) even when the ceramic loading excesses 50 vol%, leading to deteriorated mechanical properties, high loss, and low breakdown strength [43].…”

Significantly Enhanced Energy Storage Density by Modulating the Aspect Ratio of BaTiO3 Nanofibers

“…In addition, recent studies have demonstrated that the morphology and geometry of ceramic nanoparticles influence the dielectric properties of nanocomposites222324. For 0–3 type ceramic-polymer nanocomposites, where spherical zero-dimensional ceramic nanoparticles are embedded in a three-dimensionally connected polymer matrix, a high volume fraction (>50 vol%) of nanoparticles is necessary to achieve a high permittivity nanocomposite.…”