•The interaction between ILs and >CF2 groups of PVDF can bring more polar phase for PVDF composites.•The incorporation of ILs into the matrix can accelerate dc conductivity.•The effect of IL on charge carrier movement mechanism was resulted from the increase of ion mobility.To investigate the effects of 1-benzyl-3-methylimidazolium hexafluorophosphate on the crystal phase, morphology and dielectric relaxation behavior of poly(vinylidene fluoride) (PVDF), a series of PVDF/IL composites have been prepared using solution-cast method. The interaction between ILs and >CF2 groups of PVDF can facilitate the PVDF chains in amorphous area to form more polar phase for PVDF composites. In the frequency spectra of PVDF composites, MWS interfacial polarization, electrode polarization and dc conductivity resulted in high values of dielectric permittivity. The incorporation of ILs into the matrix can accelerate dc conductivity. The effect of IL on charge carrier movement mechanism was resulted from the increase of ion mobility induced by polar phase crystal and ion concentration.

•P[MPEGMA-IL] can improve the dispersion of Gra in PLA matrix.•P[MPEGMA-IL] and Gra can enhance the cold crystallization of composite.•Modified Gra can increase the mobile charge carriers at the interphase.•Modified Gra can increase the dielectric strength of interfacial polarization.To investigate the effect of modified graphene (Gra) by poly(methoxy poly(ethylene glycol) monomethacrylate-co-1-vinyl-3-ethylimidazolium bromide) (P[MPEGMA-IL]) on crystallization and dielectric behavior for poly(lactic acid) (PLA), the neat PLA and its composites were fabricated via solution blending and hot pressing. P[MPEGMA-IL] can improve the dispersibility of Gra in PLA matrix. The crystallization rate of PLA composites was increased with increasing the content of P[MPEGMA-IL] and Gra due to the plasticizing effect of P[MPEGMA-IL] and the nucleating effect of better-dispersed Gra. In the frequency spectra of PLA composites treated by cold crystallization process, α relaxation and interfacial polarization resulted in high values of dielectric permittivity. The incorporation of modified Gra into the matrix can accelerate interfacial polarization. The effect of modified Gra on charge carrier movement mechanism was resulted from the increase of the mobile charge carriers at the interphase and the dielectric strength of interfacial polarization.Download high-res image (213KB)Download full-size image

•IL can increase the conductivity of CB-IL/SR composites.•The CB-IL-5/SR composite has higher piezoresistivity and better repeatability.•The CB-IL-5/SR composite has shorter relaxation time.•Excellent piezoresistive behavior is due to the plasticizing effect of IL.High temperature vulcanized silicone rubber (SR) based nanocomposites with carbon black (CB) and ionic liquid-modified carbon black (CB-IL) as fillers were fabricated using mechanical mixing method and their piezoresistive properties were carefully characterized. 1-hexadecyl-3-methylimidazolium bromide (IL) can improve the dispersibility of CB in SR matrix by morphology characterization. The CB-IL/SR composites showed a lower percolation threshold compared with CB/SR composites. The CB-IL/SR composite with 5 vol% content of CB-IL shows higher piezoresistivity, better repeatability and shorter relaxation time due to the plasticizing effect of IL. The results suggest that the CB-IL/SR composites provide a new route toward fabrication of flexible piezoresistive sensors and wearable electronic devices.

To investigate the effects of graphene (Gra) modified by a long alkyl chain ionic liquid (1-hexadecyl-3-methylimidazolium bromide, IL) on the crystallization kinetics behavior of poly(vinylidene fluoride) (PVDF), a series of PVDF/IL blend, PVDF/Gra and PVDF/IL/Gra nanocomposites have been prepared using a solution-cast method. The crystallization kinetics and corresponding crystal structure have been investigated using differential scanning calorimetry (DSC), polarized optical microscopy (POM) and X-ray diffraction spectroscopy (XRD). The crystallization kinetic parameters, such as relative crystallinity (Xt), crystallization half time (t1/2), crystallization rate constant (Z), Avrami exponents (n) and activation energy (Ea), have been determined by both isothermal and non-isothermal techniques. In the isothermal and non-isothermal crystallization process, for PVDF/0.5IL/0.5Gra, IL and Gra can facilitate nucleation to decrease Ea; moreover, the synergistic efforts of IL and Gra can maintain appropriate crystallization rate to form the β phase extruded form the α phase. The positive effect on the crystallization of PVDF may be ascribed not only to the existence of Gra–cation interaction between the imidazolium cation and the aromatic carbon ring structure, but also to the electrostatic interaction between the CF2 group of the polymer backbone and imidazolium cation.

A series of nanocomposites based on the biodegradable plastic, polylactide (PLA), have been prepared by melt-blending with graphene (Gra) and ionic liquid containing phosphonium ([PCMIM]PF6, IL) surface-functionalized graphene (GIL). The morphology, mechanical properties, thermal stability and burning behaviour of the composites were investigated by Field Emission Scanning Electron Microscopy (FESEM), tensile test, impact test, Thermogravimetric Analysis (TGA), Limiting Oxygen Index (LOI), UL-94 test and Cone Calorimeter Test (CCT), respectively. The surface morphology and chemical structure of the char residues were explored by FESEM and Raman spectroscopy. It is confirmed that the fire-retardant performance of the PLA/GIL composites was significantly improved compared to PLA/IL and PLA/Gra; the CCT data showed a reduction in heat release rate and total heat released with increase of the char residue from the TGA results. It revealed that the catalytic charring effect of the ionic liquid, the physical isolating effect of graphene, and the combined effect of both the ionic liquid and graphene (forming continuous and compact char layers) were very efficient in improving the flame retarding properties of PLA/GIL nanocomposites.