Session Chair: Shinji Ando, Tokyo Institute of Technology Session Chair: Jun Wei, Singapore Institute of Manufacturing Technology, Agency for Science, Technology and Research (A*STAR)
4:00pm - 4:30pm Invited
Graphene/Polymer Functional Nanocomposites
Beijing Key Laboratory of Advanced Functional Polymer Composites, College of Materials Science and Engineering, Beijing University of Chemical Technology, China
To realize the potential of graphene, its modification, dispersion and distribution in polymers need to be addressed. As a precursor of graphene, graphene oxide (GO) has been used to prepare functional polymer nanocomposites [1-4]. (1) An efficient one-step approach is developed to functionalize and in situ reduce GO with octadecylamine (ODA) without the use of conventional chemical reducing agents. Different from GO, ODA-functionalized RGO (RGO-ODA) becomes not only hydrophobic but also electrically conductive. Interestingly, the conductivity of RGO-ODA is further improved by incidental thermal reduction during the compression-molding of its polystyrene (PS) nanocomposites. The nanocomposites exhibit a sharp transition from electrically insulating to conducting with a low percolation threshold. (2) The chemical reduction and surface functionalization of GO is also realized during the in situ polymerization of phenol and formaldehyde in the presence of GO. The resultant nanocomposites are electrically conductive due to the incidental reduction of GO by phenol monomer during the in situ polymerization. (3) To efficiently construct a three-dimensional (3D) conducting network of graphene sheets, graphene aerogel is prepared by in situ reduction-assembly method with para-phenylene diamine as the reducing and functionalizing agent of GO. The preformed 3D aerogel exhibits highly porous structure, low density, and high electrical and mechanical properties. Its epoxy nanocomposites show good electrical conductivity and compressive properties.
Financial support from the National Natural Science Foundation of China (51533001, 51521062) and the Fundamental Research Funds for the Central Universities (YS201402) is gratefully acknowledged.
4:30pm - 5:00pm Invited
Mechanical Properties of Cellular Graphene and their Sensor Applications
Shaohong LUO1, Yimin SUN1, Yarjan SAMAD2, Kin LIAO1
1Khalifa University, United Arab Emirates; 2University of Cambridge, United Kingdom
In this talk we first focus on the mechanical properties of cellular graphene (CG), and the applications of graphene, and cellular graphene for sensors. We report a novel, facile, two-step, adaptable and scalable method of preparing free-standing CG with tunable densities and adjustable shapes and sizes. The CG samples fabricated possess some interesting mechanical behaviors as well as excellent electrical conductivities, reaching 160 S/m, and show insignificant decrease in electrical conductivities when infiltrated with high viscosity PDMS. The CG-PDMS composite was tested for its application as strain/pressure sensor. The composite loaded in compression shows large changes in resistance in response to application of small strains or pressures. Different densities of CG show different sensitivity to applied compressive strain/pressure; therefore, these CG-PDMS composite can be used for a range of low and high strain/pressure sensing applications.
We also report that simple sewing thread fibers and fiber mats such as Nylon® can be used as supersensitive and durable pressure and strain sensors after a slight modification with reduced graphene oxide (rGO). Pristine Nylon® fibers were coated with rGO by a novel electrostatic coating method. The rGO coated fabric show smooth coating discretely wrapping every fiber downright. The in situ twisting of the fiber observed under a scanning electron microscope shows that the rGO coating remains intact even after twisting the fiber to angles as high as 1800°. These electrically conductive fabrics have several potential applications in wearable electronic devices. We show that these rGO coated fabric and fibers are highly sensitive to external perturbation such as force or strain. The fabric’s response to applied compressive and bending stresses is recorded as the change in resistance. Single rGO coated single fibers, about 15 mm in diameter, were isolated from the fabric and were tested for their response to flexural strains. These fibers were found to sense small strains by changing the resistance in several kilo ohms. With the help of a simple circuit it is also demonstrated that the individual rGO coated fibers, arranged in a 2x2 grid and insulated from each other, can also sense the position of the applied force.
5:00pm - 5:30pm Invited
Exploiting Symmetry and Material Nonlinearity for Mechanical Metamaterials
DSO National Laboratories, Singapore
The manipulation and control of phonons is scientifically important for understanding nonlinear propagation behaviour, and technologically due to their applications ranging from sound insulation to shock dissipation. A unique challenge in phonon manipulation lies in the material‘s inherently nonlinear response, which stems from the intriguing structure of the different materials across multiple length scales, from the atomic to the meso-scale that collectively give rise to this rich behavior.
Phononic metamaterials (PMM) enable access to exotic propagation behaviour, such as negative refraction and super-absorption, through structuring at a particular length scale. Dynamic behavior in PMMs is typically realized through affine deformation or elastic instabilities, leading to structural changes and hence dispersion behaviour. We propose that by harnessing the intrinsic nonlinear responses in materials together with artificial structural symmetry, one may arrive at novel methods of controlling wave propagation behavior. One example of this is in spider silk fibres, where we theoretically and experimentally observed an indirect polarization band gap (30%) and negative index behaviour; we further demonstrated that these properties can be dynamically and reversibly tuned with large amplitude strains (up to ±20%).  The origin of this band gap is distinct from Bragg scattering or resonance hybridization, while the negative index behavior arises from the elastic nonlinearity.
We further show that by designing the multiple length scales governing both the intrinsic material response and wave propagation through symmetry principles, we are able to control the nonlinear wave propagation characteristics in intriguing ways. Potential applications ranging from reconfigurable phonon polarizers to ultra-compact sound isolation will be discussed.
 D. Schneider, N. Gomopoulos, C.Y. Koh, P. Papadopoulos, F. Kremer, E. L. Thomas & G. Fytas, Nonlinear control of high-frequency phonons in spider silk, Nature Materials, 15, 1079 (2016)
5:45pm - 6:00pm Oral
Electromagnetic Interference Shielding Properties and Mechanisms of Ultralight Graphene Aerogels
1Key Laboratory of Optoelectronic Chemical Materials and Devices, Ministry of Education, School of Chemical and Environmental Engineering, Jianghan University, China; 2Temasek Laboratories, Nanyang Technological University, Singapore; 3School of Material Science and Engineering, Nanyang Technological University, Singapore
Advanced electromagnetic interference (EMI) shielding materials for the prevention of damages arising from the unwanted EMI are essential in modern electrical and electronic devices. Among the library of EMI shielding materials, graphene was demonstrated as one of the best candidate owing to its high electrical conductivity and corrosion resistance. Considering the stringent fuel-economy standard in applications, lightweight EMI shielding materials are much preferred. In this work, we prepared ultralight (~4.5-5.5 mg/cm3) graphene aerogels (GAs) by two different reduction methods, i.e. chemical reduction and thermal reduction for comparative studies to understand the dominating factors influencing the EMI shielding performance and mechanisms of GAs with respect to the unique porous structure of GAs and the intrinsic properties of the reduced graphene oxide (rGO) sheets, such as nitrogen-doping, residual functional side group and carbon main structures. The EMI shielding effectiveness (SE) of chemically reduced GAs (GAC) was increased from 20.4 to 27.6 dB at thickness of 2.5 mm when the GO was reduced by high concentration of hydrazine vapor. The EMI SE of thermally reduced GAs (GAT) reached 40.2 dB. It was found that the introduction of nitrogen atoms through chemical reduction induced localized charges on the carbon backbone leading to strong polarization effects of GAC. The relatively incomplete reduction caused a large number of side polar groups which prevented the graphene sheets from π-π stacking. In contrast, the higher extent of reduction of graphene sheets in GAT left a smaller amount of side polar groups and formed more sp2 graphitic lattice, both factors favoured π-π stacking between the adjacent graphene sheets, resulting in higher electrical conductivity and enhanced EMI SE. The EMI shielding performance of the GAs prepared outperformed the recent reported porous carbon materials with respect to the absolute SE value at the similar thickness and/or density.