Kin Liao

Interfacial characteristics of a carbon nanotube–polystyrene composite system

The performance of a composite material system is critically controlled by the interfacial characteristics of the reinforcement and the matrix material. Here we report a study on the interfacial characteristics of a carbon nanotube (CNT)-reinforced polystyrene (PS) composite system through molecular mechanics simulations and elasticity calculations. In the absence of atomic bonding between the reinforcement and the matrix material, it is found that the nonbond interactions consists of electrostatic and van der Waals interaction, deformation induced by these forces, as well as stress/deformation arising from mismatch in the coefficients of thermal expansion. All of these contribute to the interfacial stress transfer ability, the critical parameter controlling material performance. Results of a CNT pullout simulation suggests that the interfacial shear stress of the CNT–PS system is about 160 MPa, significantly higher than most carbon fiber reinforced polymer composite systems.

Bio‐Inspired Nacre‐like Composite Films Based on Graphene with Superior Mechanical, Electrical, and Biocompatible Properties

Bio-inspired multifunctional composite films based on reduced poly(vinyl alcohol)/graphene oxide (R-PVA/GO) layers are prepared by a facile solution casting method followed by a reduction procedure. The resulting films with nacre-like, bricks-and-mortar microstructure have excellent mechanical properties, electrical conductivity, and biocompatibility.

Mechanical properties and interfacial characteristics of carbon-nanotube-reinforced epoxy thin films

Multiwalled carbon nanotubes (MWNT) reinforced epoxy composite thin films were prepared by a microfabrication process and their elastic modulus was determined using a shaft-loaded blister test and linear and nonlinear elasticity models. Compared to net resin thin films, a 20% increase in elastic modulus was seen when 0.1 wt % MWNTs were added, suggesting MWNT alignment by spin coating. Electron microscopic observations of the fracture surfaces suggested high interfacial shear stress between MWNTs and the epoxy matrix, a result supported by both molecular mechanics simulation and micromechanics calculations.

Tensile properties, tension–tension fatigue and biological response of polyetheretherketone–hydroxyapatite composites for load-bearing orthopedic implants

Polyetheretherketone-hydroxyapatite composites were developed as alternative materials for load-bearing orthopedic applications. The amount of hydroxyapatite (HA) incorporated into the polyetheretherketone (PEEK) polymer matrix ranges from 5 to 40 vol% and these materials were successfully fabricated by injection molding. This study presents the mechanical and biological behavior of the composite materials developed. It was found that the amount of HA in the composite influenced the tensile properties. Dynamic behavior under tension-tension fatigue revealed that the fatigue-life of PEEK-HA composites were dependent on the HA content as well as the applied load. The biological responses of PEEK-HA composites carried out in vivo verified the biocompatibility and bioactive nature of the composite materials.

Effects of Environmental Aging on the Properties of Pultruded GFRP

Abstract Pultruded glass–fiber-reinforced vinyl ester matrix composite coupons were subjected to environmental aging in order to study their durability since such composites are of interest for infrastructure applications. Specimens were tested as-received and after aging in water or salt solutions at room temperature (25°C) or in water at 75°C for various times. The flexural properties (strength and modulus) were determined for bending perpendicular to the 0° orientations (0° being the pull direction) for all aging conditions. In addition, flexural properties in the 90° orientation and tensile properties in the 0° orientation were also measured for the as-received specimens and the specimens exposed to selected aging conditions. Both strengths and moduli were generally found to decrease with environmental aging. Comparing the size of the fracture mirrors on the broken ends of the fibers in aged and un-aged samples suggested that environmental aging decreased the in situ fiber strength. In addition, examination of the failure surfaces and comparisons between the strength of the 90° specimens suggested that degradation of the fiber/matrix interphase region also occurred during the aging process.

Synergistic effect of hybrid carbon nantube–graphene oxide as a nanofiller in enhancing the mechanical properties of PVA composites

A poly(vinyl alcohol) (PVA) based nanocomposite using fully exfoliated graphene oxide (GO) sheets and multi-walled carbon nanotubes (CNTs) were prepared via a simple procedure. It is confirmed from optical imaging that dispersion of CNTs in the PVA matrix can be significantly improved by adding GO sheets. Molecular dynamics (MD) simulations suggest that the GO–CNT interaction is strong and the complex is thermodynamically favorable over agglomerates of CNTs. The GO–CNT scroll-like structure formed with the hydrophilic outer surface of GO can be well dispersed in water. More important, a synergistic effect arises from the combination of CNT and GO, the GO–CNT/PVA composite films show superior mechanical properties compared to PVA composite films enhanced by GO or CNT alone, not only the tensile strength and Youngs modulus of the composites are significantly improved, but most of the ductility is also retained. The enhanced mechanical properties of the GO–CNT/PVA composite film can be attributed to the fully exploited reinforcement effect from GO and CNT via good dispersion.

Graphene Foam Developed with a Novel Two-Step Technique for Low and High Strains and Pressure-Sensing Applications

Freestanding, mechanically stable, and highly electrically conductive graphene foam (GF) is formed with a two-step facile, adaptable, and scalable technique. This work also demonstrates the formation of graphene foam with tunable densities and its use as strain/pressure sensor for both high and low strains and pressures.

Environmental effects on bamboo-glass/polypropylene hybrid composites

The effects of environmental aging and accelerated aging on tensile and flexural behavior of bamboo fiber reinforced polypropylene composite (BFRP) and bamboo-glass fiber reinforced polypropylene hybrid composite (BGRP), all with a 30% (by mass) fiber content, were studied by exposing the samples in water at 25°C for up to 1600 h and at 75°C for up to 600 h. Reduction in tensile strength for BFRP and BGRP was 12.2% and 7.5%, respectively, after aging at 25°C for about 1200 h. Tensile and flexural strength of BFRP and BGRP were reduced by 32%, 11.7%, and 27%, 7.5% respectively, after aging at 75°C for 600 h. While the strengths of the bamboo fiber reinforced composites reduce with sorption time and temperature, the environmental degradation process can be delayed by adding a small amount of glass fiber. Moisture sorption and strength reduction are further suppressed by using maleic anhydride polypropylene (MAPP) as a coupling agent in both types of composite system.

Tension-tension fatigue behavior of unidirectional single-walled carbon nanotube reinforced epoxy composite

nanyang technol univ, sch mech & prod engn, singapore 639798, singapore. chinese acad sci, met res inst, shenyang natl lab mat sci, shenyang 110016, peoples r china.;liao, k (reprint author), nanyang technol univ, sch mech & prod engn, singapore 639798, singapore

Novel graphene foam composite with adjustable sensitivity for sensor applications.

In this study, free-standing graphene foam (GF) was developed by a three-step method: (1) vacuum-assisted dip-coating of nickel foam (Ni-F) with graphene oxide (GO), (2) reduction of GO to reduced graphene oxide (rGO), and then (3) etching out the nickel scaffold. Pure GF samples were tested for their morphology, chemistry, and mechanical integrity. GF mimics the microstructure of Ni-F while individual bones of GF were hollow, because of the complete removal of nickel. The GF-PDMS composites were tested for their ability to sense both compressive and bending strains in the form of change in electrical resistance. The composite showed different sensitivity to bending and compression. Upon applying a 30% compressive strain on the GF-PDMS composite, its resistance increased to ∼120% of its original value. Similarly, bending a sample to a radius of 1 mm caused the composite to change its resistance to ∼52% of its original resistance value. The relative change in resistance of the composite by an applied pressure/strain can be tuned to considerably different values by heat-treating the GF at different temperatures prior to infusing PDMS into its scaffold. Upon heat treating the GF at 800 °C prior to PDMS infusion, the GF-PDMS demonstrated ∼10 times better sensitivity than the untreated sample for a compressive strain of 20%. The composite was also tested for its ability to retain a change in electrical resistance when a brief load/strain is applied. The GF-PDMS composite was tested for at least 500 cycles under compressive cyclic loading and showed good electromechanical durability. Finally, it was demonstrated that the composite can be used to measure human blood pressure when attached to human skin.