Enhanced dielectric performance of PDMS-based three-phase percolative nanocomposite films incorporating a high dielectric constant ceramic and conductive multi-walled carbon nanotubes†
Three-phase composite films CCTO@MWCNT/PDMS with enhanced dielectric constant (ε) and low dielectric loss are prepared by embedding covalently bonded calcium copper titanate (CaCu3Ti4O12, CCTO) with multi-walled carbon nanotubes (MWCNTs) composite nanoparticles (CCTO@MWCNT), forming a chain-ball structure, into the polydimethylsiloxane (PDMS) matrix. To impede the natural stacking of MWCNTs, CCTO particles are functionalized first with a silane coupling agent containing amino groups, and then react with carboxyl-functionalized MWCNTs (MWCNT-COOH) to achieve the strong linkage between CCTO and MWCNTs, confirmed by the FTIR spectrum and SEM images, etc. The chain-ball CCTO@MWCNT nanoparticles have effectively improved the dielectric permittivity of PDMS. The dielectric constant of the CCTO@MWCNT/PDMS composite film, agreeing well with the percolation theory, is up to 2133 at 1 kHz, higher than that of pure PDMS by a factor of 700, when the volume fraction of MWCNTs approaches the percolative threshold. Meanwhile, the dielectric loss is only 0.19. For comparison, CCTO/PDMS and MWCNT/PDMS films are prepared and investigated as well. The Yamada model can effectively predict the dielectric constant of CCTO/PDMS composite films. The dielectric constants of CCTO/PDMS and MWCNT/PDMS films are 1/180 and 1/6, respectively, in comparison with that of CCTO@MWCNT/PDMS. The tensile strength of CCTO@MWCNT/PDMS approaches 1.12 MPa, 3 times higher than that of pure PDMS.