Yarjan Abdul Samad

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.

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.

From cotton to wearable pressure sensor

In this work, carbon cottons (CC) with moderate electrical conductive (11 S m−1) were prepared from cotton via a simple pyrolysis process. Flexible and electrical conductive CC/polydimethylsiloxane (PDMS) composites were fabricated by vacuum assisted infusion of PDMS resin into a CC scaffold. Based on the CC/PDMS composites prepared, a simple yet highly sensitive pressure sensor was developed, which shows a maximum sensitivity of 6.04 kPa−1, a wide working pressure up to 700 kPa, a wide response frequency from 0.01 to 5 Hz, and durability over 1000 cycles. Based on our knowledge, the pressure sensitivity of the CC/PDMS sensor is only next to the record value in a pressure sensor (8.4 kPa−1). By integrating the pressure sensor with a sport shoe and waist belt, we demonstrate that the real time sport performance and health condition could be monitored. Notably, the device fabrication process is simple and scalable with low-cost cotton as raw material. The CC/PDMS composites are believed to have promising potential applications in wearable electronic devices such as, human-machine interfacing devices, prosthetic skins, sport performance, and health monitoring.

Highly electrically conductive nanocomposites based on polymer-infused graphene sponges.

Conductive polymer composites require a threedimensional 3D network to impart electrical conductivity. A general method that is applicable to most polymers for achieving a desirable graphene 3D network is still a challenge. We have developed a facile technique to fabricate highly electrical conductive composite using vacuumassisted infusion of epoxy into graphene sponge GS scaffold. Macroscopic GSs were synthesized from graphene oxide solution by a hydrothermal method combined with freeze drying. The GSepoxy composites prepared display consistent isotropic electrical conductivity around 1Sm, and it is found to be close to that of the pristine GS. Compared with neat epoxy, GSepoxy has a 12ordersofmagnitude increase in electrical conductivity, attributed to the compactly interconnected graphene network constructed in the polymer matrix. This method can be extended to other materials to fabricate highly conductive composites for practical applications such as electronic devices, sensors, actuators, and electromagnetic shielding.

From biomass to high performance solar–thermal and electric–thermal energy conversion and storage materials

We demonstrate that lightweight, highly electrically conductive, and three-dimensional (3D) carbon aerogels (CAs) can be produced via a hydrothermal carbonization and post pyrolysis process using various melons as raw materials. This two-step process is a totally green synthetic method with cheap and ubiquitous biomass as the only raw material. These black-colored, highly electrically conductive and 3D structured CAs are ideal materials for energy conversion and storage. Paraffin wax was impregnated into the CA scaffold by vacuum infusion. The obtained CA–wax composites show excellent form-stable phase change behavior, with a high melting enthalpy of 115.2 J g−1. The CA–wax composites exhibit very high solar radiation absorption over the whole UV-vis-NIR range, and 96% of light can be absorbed by the phase-change composite and stored as thermal energy. With an electrical conductivity of 3.4 S m−1, the CA–wax composite can be triggered by low electric potential to perform energy storage and release, with an estimated electric–heat conversion efficiency of 71.4%. Furthermore, the CA–wax composites have excellent thermal stability with stable melting–freezing enthalpy and excellent reversibility. With a combination of low-cost biomass as the raw materials, a green preparation process, low density, and excellent electrical conductivity, the 3D CAs are believed to have promising potential applications in many energy-related devices.

Synergistic toughening of epoxy with carbon nanotubes and graphene oxide for improved long-term performance

Epoxy based nanocomposites using graphene oxide (GO) sheets dispersed multi-walled carbon nanotubes (CNTs) as combination fillers were prepared using an in situ polymerization technique. A remarkable synergetic effect was observed between CNTs and GO sheets which improved the mechanical properties of the epoxy. It was confirmed by optical and field-emission scanning electron microscopy (FESEM) images that the dispersion of CNTs in epoxy matrix can be significantly improved by adding GO sheets. The overall mechanical properties of CNT–GO/epoxy composites were greatly enhanced with only adding 0.04 wt% (percent by weight) CNTs and 0.2 wt% GO sheets. Moreover, the fatigue and creep rupture lives of pure epoxy was also significantly increased by the addition of GO dispersed CNTs. Approximately a 950% improvement in fatigue life, and 400% improvement in creep rupture life were observed at the applied stress levels tested.

Non-destroyable graphene cladding on a range of textile and other fibers and fiber mats

Electrically insulating textile and synthetic fibers were cladded with chemically modified graphene via a three-step technique to induce electrical conductivity. Electrical conductivities of 13 and 4.5 S cm−1 were obtained for aramid and nylon fibers, respectively. The graphene cladding is non-destroyable when washed in detergent or sonicated.

Nanomanifestations of Cellulose: Applications for Biodegradable Composites

High-strength and high-stiffness nanocelluloses are extracted from native cellulose which is an abundant and sustainable material. Cellulose can come with different manifestations in terms of morphologies and microstructure. The variation of cellulose morphology at the nanoscale comes from the way the material is processed or extracted. We discuss four types of nanocellulose manifestations, namely, nanocrystalline cellulose, electrospun cellulose, microfibrillated cellulose, and bacterial cellulose. The low density and biodegradable nature of these cellulose manifestations make them very desirable material. Nanocomposites prepared from cellulose are of great interest, owing to the many end-use applications. If they are to be used with hydrophobic polymers and ensure a good level of dispersion, chemical surface modification of nanocelluloses is necessary. In addition to the interfacial characteristics, the nanocellulose morphology can also dictate the processing method of the nanocomposites. In this chapter, we put particular emphasis on two important applications of nanocellulose-reinforced biodegradable polymers: packaging and tissue engineering.

Voltage and Photo Driven Energy Storage in Graphene Based Phase Change Composite Material

In this study, a phase change composite material was developed with a graphene sponge (GS) skeleton and Paraffin-wax matrix. The GS was synthesized by hydrothermal treatment and subsequent freeze drying and the Paraffin-wax/GS (PGS) composite was developed by vacuum infusion process of molten Paraffin-wax inside the GS skeleton. The morphological studies of the PGS composite were performed with a Scanning Electron Microscope and Atomic Force Microscope. The PGS composite was characterized for its storage of electrical energy from an applied voltage, in the form of thermal energy, and the storage of thermal energy from xenon light of controlled power. Successful storage of electrical energy in the form of thermal energy is demonstrated by the PGS composite on the application of different voltages. A temperature of 60, 120 and 150 °C is reached on the application of voltages 5, 10 and 15 V respectively before a thermal balance is achieved. Exposing the PGS composite to the xenon light of controlled power shows improved energy absorption than that of the pristine Paraffin-wax and shows a 10 °C improvement in the temperature before reaching the thermal balance. Thermal studies done via a Differential Scanning Calorimetric (DSC) shows that there is no chemical reaction occurring between the Paraffin-wax and the GS as similar DSC curves are obtained for both the samples.