Shaodi Zheng

A highly-deformable piezoresistive film composed of a network of carbon blacks and highly oriented lamellae of high-density polyethylene

The electrical resistance change of highly extensible films consisting of a network of carbon blacks in high-density polyethylene, with different regularity of stacked lamellae, is investigated. The film was fabricated by melt mixing of high-density polyethylene (HDPE) and carbon black (CB) via cast film extrusion. The morphology of particle network and regularity of stacked lamellae were affected by draw ratio during the cast film extrusion process. Testing has shown that the regularly stacked lamellar structure furnishes the film with hard elastic behavior and is conducive to the enhancement of the reversible level for the conductive film, which correlates with the piezoresistance response during the stretching and strain recovery. A rebound peak of R/R0 is observed at the beginning of each loading cycle within the relatively low deformation level and a marked growth of the amplitude of R/R0, as the number of cycle increases, is observed within the high deformation level for the film with highly regular stacked lamellae. It indicates that the regularity of stacked lamellar structure of matrix has a significant influence on the piezoresistivity of the film. The results could be utilized for the development of smart sensing and structural health monitoring of CB composite materials.

Phase morphology control and the selective localization of MWCNT for suppressing dielectric loss and enhancing the dielectric constant of HDPE/PA11/MWCNT composites

A nanocomposite with a giant dielectric constant and suppressed dielectric loss was obtained from the high-density polyethylene (HDPE)/polyamide-11 (PA11)/multiwalled carbon nanotube (MWCNTs) composites, by tailoring the selective localization of MWCNTs in the PA11 phase and improving the interfacial interaction between HDPE and PA11 through the addition of high density polyethylene grafted maleic anhydride (HDPE-g-MAH). The effect of the addition of the polar component compatibilizer (HDPE-g-MAH) and PA11 on the dielectric properties of the HDPE/MWCNT composites was systematically studied. Through the addition of the polar phase (PA11) into the HDPE/MWCNT composites as the dispersed phase, with MWCNTs selectively localized in it, the dielectric properties were improved. Subsequently, as the compatibilizer (HDPE-g-MAH) was added into the HDPE/PA11/MWCNT composites, the interface between HDPE and PA11 became indistinct and PA11 in the form of dispersed phase coated MWCNTs could generate some degree of combination, to cause the size of the dispersed phase to get larger. Therefore, the dielectric constant of HDPE/PA11/MWCNT composites containing compatibilizer was up to 4000 at 3 wt% MWCNT and 103 Hz, which was attributed to the selective localization of MWCNTs to reduce the distance between the MWCNTs and the formation of larger sized microcapacitors (PA11 coated MWCNTs), and dielectric loss was still maintained at a low value (∼2 at 103 Hz), which was due to the stronger interfacial interaction between HDPE and PA11. The composites displayed advantages of excellent dielectric properties and good processability, which are suitable for the development of dielectric materials for energy storage.

New understanding for the formation of conductive network in the nanocomposites during the crystallization of matrix

Crystallization behavior of conductive composite has a great effect on the formation of conductive network. But very few studies have exposited, specially on the micro level, the evolution of conductive network during the crystallization of matrix. In this study, the conductive network was found to be destroyed by crystallization behavior of isotactic polypropylene (iPP) matrix, and the carbon black (CB) particles were rejected to the amorphous region or the inter-lamellar of spherulite. By comparison, the low-structure carbon black (LCB) filled system was more sensitive to the crystallization of matrix than the high-structure carbon black (HCB) filled system because of the morphology and interaction force of the CB primary aggregate. A secondary increase in volume resistivity during terminal crystallization was observed in iPP/LCB composite when it isothermally crystallized at a certain temperature. In that case, an analysis of crystallization kinetics of composites through a modified Lauritzen-Hoffman model indicated that the transition from regime I→II in the isothermal crystallization process of iPP matrix showed significant influence on the network formation of LCB particles.

Enhancing the conductivity of isotactic polypropylene/polyethylene/carbon black composites by oscillatory shear

The influence of oscillatory shear on the conductivity of the isotactic polypropylene/polyethylene/carbon black composites is studied. It is found that the oscillatory shear under high strain amplitude can enhance the conductivity of the ternary composites with a HDPE/CB concentration in the percolation region. This is related to the fact that the high-strain oscillatory shear can improve the continuity of the conductive HDPE/CB phase in the composites. This finding has not been previously reported, and it may be used in industry to improve the conductivity of the ternary conductive composites with a low filler loading.

Improved dielectric properties of polymer-based composites with carboxylic functionalized multiwalled carbon nanotubes

The biggest issues in the preparation of carbon nanotube (CNT)-reinforced composites reside in efficient dispersion of CNT into polymer matrix. In our work, a simple acid treatment method was adopted to obtain carboxylic functionalized multiwalled nanotubes (MWNTs), thus improving the dispersion of CNT and interaction between particles and polymer matrix. X-ray photoelectron spectroscopy and Fourier transform infrared showed that the carboxylic groups were introduced onto the surface of MWNTs. The Raman spectroscopy showed that the amorphous carbon materials and impurities decreased after acid treatment. The electrical and dielectric properties of the Polyamide-11 (PA11)-based composites filled with pristine multiwalled nanotubes (p-MWNTs) and carboxylic functionalized multiwalled nanotubes (c-MWNTs) were investigated. The biggest dielectric constant of PA11/c-MWNTs composites, which was about twice as high as that of PA11/p-MWNTs composites at room temperature and 103 Hz (345–610), was obtained, accompanied by a lower dielectric loss. The formation of abundant microcapacitors and improved interfacial polarization effect by improving the dispersion of MWNTs in the composites via carboxylic functionalization was the main reason for the excellent dielectric properties of PA11/c-MWNTs composites.