Benhui Fan

Design of Electrically Conductive Structural Composites by Modulating Aligned CVD-Grown Carbon Nanotube Length on Glass Fibers

Function-integration in glass fiber (GF) reinforced polymer composites is highly desired for developing lightweight structures and devices with improved performance and structural health monitoring. In this study, homogeneously aligned carbon nanotube (CNT) shell was in situ grafted on GF by chemical vapor deposition (CVD). It was demonstrated that the CNT shell thickness and weight fraction can be modulated by controlling the CVD conditions. The obtained hierarchical CNTs-GF/epoxy composites show highly improved electrical conductivity and thermo-mechanical and flexural properties. The composite through-plane and in-plane electrical conductivities increase from a quasi-isolator value to ∼3.5 and 100 S/m, respectively, when the weight fraction of CNTs grafted on GF fabric varies from 0% to 7%, respectively. Meanwhile, the composite storage modulus and flexural modulus and strength improve as high as 12%, 21%, and 26%, respectively, with 100% retention of the glass transition temperature. The reinforcing mechanisms are investigated by analyzing the composite microstructure and the interfacial adhesion and wetting properties of CNTs-GF hybrids. Moreover, the specific damage-related resistance variation characteristics could be employed to in situ monitor the structural health state of the composites. The outstanding electrical and structural properties of the CNTs-GF composites were due to the specific interfacial and interphase structures created by homogeneously grafting aligned CNTs on each GF of the fabric.

Influence of Thermal Treatments on the Evolution of Conductive Paths in Carbon Nanotube-Al2O3 Hybrid Reinforced Epoxy Composites

The conductive path formed by carbon nanotubes (CNTs) in a polymer matrix is one of the most attractive topics for developing multifunctional nanocomposites. In this article, we studied the evolution of conductive paths and interactions in the interfacial regions in epoxy-based composites reinforced by an urchinlike hybrid of CNTs and alumina microparticles (μAl2O3). A homogeneous dispersion of CNTs in the epoxy matrix was achieved thanks to the core-shell structures of CNTs-μAl2O3 hybrids, resulting in the interpenetrated epoxys cross-linking network that strongly bonds with CNTs. Furthermore, thermal treatments at different temperatures around the glass-transition temperature (Tg) were conducted under vacuum on composites near the percolation threshold. It was found that the dielectric behavior and the Tg were shifted in spite of the constant CNT mass fraction used. This was mainly due to the fact that thermal treatment generated the adjustment of the cross-linking network of epoxy, and the distances between adjacent CNTs were reduced gradually. This study can provide insight into the evolution of conductive paths in the interfacial regions from a more straightforward perspective.

Achieving polydimethylsiloxane/carbon nanotube (PDMS/CNT) composites with extremely low dielectric loss and adjustable dielectric constant by sandwich structure

Sandwich-structured composites of polydimethylsiloxane/carbon nanotube (PDMS/CNT) bulk between two neat PDMS thin films with different thicknesses are prepared by the spin-coating method. Taking advantage of CNTs percolation behavior, the composite keeps relatively high dielectric constant (e′u2009=u200940) at a low frequency (at 100u2009Hz). Meanwhile, due to the existence of PDMS isolated out-layers which limits the conductivity of the composite, the composite maintains an extremely low dielectric loss (tanu2009δ = 0.01) (at 100u2009Hz). Moreover, the same matrix of the out-layer and bulk can achieve excellent interfacial adhesion, and the thickness of the coating layer can be controlled by a multi-cycle way. Then, based on the experimental results, the calculation combining the percolation theory and core-shell model is used to analyze the thickness effect of the coating layer on e′. The obtained relationship between the e′ of the composite and the thickness of the coating layer can help to optimize the sandwich structure in order to obtain the adjustable e′ and the extremely low tanu2009δ.

Thickness effect on the tensile and dynamic mechanical properties of graphene nanoplatelets-reinforced polymer nanocomposites

The thickness effect of graphene nanoplatelets (GNPs) on the morphology, tensile and dynamic mechanical properties of GNPs/PMMA nanocomposites has been studied. Two types of GNPs, G5 (5xa0nm thick) and G100 (100xa0nm thick), were incorporated into a poly-methyl methacrylate (PMMA) matrix, each with four weight percentages: 0.1, 0.5, 1.0 and 5.0%. After measured by tensile test and dynamic mechanical analysis, the thinner G5 was found to improve more significantly the reinforcement of nanocomposites than G100. At 5.0xa0wt%, the Young’s modulus of G5/PMMA was 53.6% greater than that of the pure PMMA as compared to a 26.1% increase for G100/PMMA; the ultimate tensile strength of G5/PMMA was enhanced by 25.5% compared to 3.1% for G100/PMMA; the storage modulus of G5/PMMA was improved by 84.3% compared to 54.1% for G100/PMMA. The fracture toughness of both nanocomposites improved greatly at 0.1xa0wt%: a 47.9% improvement for G5/PMMA compared with pure PMMA and 20.8% for G100/PMMA, and maintained at the same level up to 1.0xa0wt%. The advantage of G5 over G100 in terms of tensile and dynamic mechanical properties enhancement was caused by its thinness, to be related to its high specific surface area.

Influences of Thermal Treatment on the Dielectric Performances of Polystyrene Composites Reinforced by Graphene Nanoplatelets

Dielectric properties of composites near percolation threshold (fc) are often sensitive to thermal treatments, and the annealing temperature is usually associated with a polymer’s rheological properties. In this study, the influences of the thermal treatment on dielectric properties are investigated for the polystyrene (PS) matrix composite reinforced by graphene nanoplatelets (GNP) fillers near fc. It can be found that the thermal treatment can not only increase the dielectric constant, but also decrease the dielectric loss for the PS/GNP composite. This interesting phenomenon possibly happens in the interfacial region of PS/GNP with the thickness about 4–6 nm according to the electron energy-loss spectroscopy (EELS) results. The free volumes around the interface can be easily altered by the movement of polymeric segments after annealing at the glass transition temperature.