Rahim Jan

Stiff, strong, yet tough free-standing dielectric films of graphene nanosheets-polyurethane nanocomposites with very high dielectric constant and loss

In this study, graphene nanosheets (GNS) prepared through a liquid exfoliation technique are dispersed in thermoplastic polyurethane (TPU) at a volume fraction (Vf) of up to 0.19. Then, the electrical and mechanical properties of the obtained composites are characterized. The dielectric spectroscopy shows an excessive variation in dielectric constant (1.1 to 3.53 × 107) and dielectric tangent loss (0.03 to 2515) with varying Vf over the frequency range of 25 kHz to 5 MHz. A considerable enhancement in electrical conductivity (DC) is found, from 3.87 × 10−10 S/m (base polymer) to 53.5 S/m for the 0.19 Vf GNS-TPU nanocomposite. The GNS-TPU composites are mechanically robust, with a considerable increase in stiffness (∼4-fold) and strength (almost twice), maintaining its ductility up to 0.09 Vf GNS. The high dielectric constant at lower frequencies is attributed to the well-established Maxwell-Wagner polarization effect, whereas the high dielectric tangent loss is due to leakage currents as a physical conducting network is formed at high filler loadings. The layered structure, high aspect ratio, and improved dispersion of GNS are the main reasons for the improvement in both the dielectric characteristics and the mechanical properties of the host polymer.

Dielectric spectroscopy of high aspect ratio graphene-polyurethane nanocomposites

High aspect ratio graphene nanosheets (GNS), prepared via liquid exfoliation, are homogeneously dispersed in thermoplastic polyurethane (TPU). Dielectric spectroscopy results are reported for these nanocomposites (up to 0.55 vol. % GNS) in the frequency range of 100 Hz to 5 MHz. The as-prepared GNS increased the AC conductivity 10–1000 times across the given frequency range. The dielectric constant is increased 5–6 times at 100 Hz for the maximum loading of GNS when compared with the pristine TPU, with subsequently high dielectric loss making them a suitable candidate for high energy dissipation applications such as EMI shielding. The temperature effects on the dielectric characteristics of 0.55 vol. % GNS/TPU nanocomposites beyond 400 K are more pronounced due to the interfacial and orientation polarization. Mechanical characteristics evaluation of GNS/TPU composites shows a marked increase in the ultimate tensile strength without compromising their ductility and stiffness.

Liquid exfoliated graphene smart layer for structural health monitoring of composites

Graphene nanosheets were exfoliated from graphite using liquid exfoliation method. Smart sensing layer was prepared by dispersing graphene nanosheets in thermoplastic polyurethane. The smart sensing layers thus obtained were pasted on to the glass fiber laminated composite specimens. The sensing layer due to its piezoresistivity was employed for detecting strains in the composite specimens. The results show that the smart sensing layer can be employed for strain sensing in the composite structures. The results hold promise for various applications of these sensors for structural health monitoring in composite parts.

Synthesis and Characterization of MoS2/TiO2 Nanocomposites for Enhanced Photocatalytic Degradation of Methylene Blue under Sunlight Irradiation

2D nanosheets/ nanoparticles based MoS2/TiO2 nanocomposites were prepared in different weight compositions which were further employed to investigate photocatalytic degradation of methylene blue. Anatase TiO2 powder was prepared via sol-gel reflux method using titanium tetraisopropoxide as Ti precursor. MoS2/TiO2 nanocomposites were prepared by in situ addition of exfoliated MoS2 (2D-nanosheets) in different weight ratios of 0.1%, 0.5%, 1%, 2% and 5% in TiO2 sol. Surface morphology, phase analysis, optical properties were studied using SEM, XRD, UV-Vis spectroscopy respectively. SEM results showed that TiO2 nanoparticles were completely adsorbed over the surface of MoS2 sheets as reflux synthesis was employed. Efficient charge carrier separation was achieved which reduced recombination, and hence, enhanced photo-degradation of methylene blue was observed. The hetero-structures showed less operation time in sunlight for photodegradation of methylene blue and a highest rate constant was observed by 2 wt.% loading of MoS2 on TiO2. These composites can also be used commercially as they show promising results.

Boron nitride-polymer composites: Mechanical properties evaluation at various strain ratios

Liquid phase exfoliation method is used to achieve three different sized (L≈0.4, 1, 1.9 µm) hexagonal Boron Nitride (hBN) nanosheets by changing the centrifugation rate. Mechanical properties of polymer composites are evaluated with hBN nanosheets utilized as reinforcement filler in polyvinylchloride (PVC) matrices. In an earlier work, uniaxial drawing (300%) was successfully employed to enhance the strength and modulus of these composites from 65–82 MPa and 1.45–1.8 GPa respectively. Here, we try to elaborate more the effect of uniaxial drawing on polymer nanocomposites (0.2 wt % for all three sizes BN) at various strain ratios (100–500%). The ultimate tensile strength (UTS) and Youngs modulus (Y) have experienced maximum increase at 450–500% strain are 3 GPa and 240 MPa respectively. Alignment and improved dispersion of hBN inside are the possible reasons for enhancement in mechanical properties; along with the strain induced delamination achieved with uniaxial drawing. The enhancement in mechanical characteristics of polymer composites is close to the theoretically predicted values of hBN.

Evaluating Mechanical Properties of Few Layers MoS2 Nanosheets-Polymer Composites

The reinforcement effects of liquid exfoliated molybdenum disulphide (MoS2) nanosheets, dispersed in polystyrene (PS) matrix, are evaluated here. The range of composites (0~0.002 volume fraction () MoS2-PS) is prepared via solution casting. Size selected MoS2 nanosheets (3~4 layers), with a lateral dimension 0.5~1 µm, have improved Young’s modulus up to 0.8 GPa for 0.0002 MoS2-PS as compared to 0.2 GPa observed for PS only. The ultimate tensile strength (UTS) is improved considerably (~×3) with a minute addition of MoS2 nanosheets (0.00002 ). The MoS2 nanosheets lateral dimension and number of layers are approximated using atomic force microscopy (AFM). The composites formation is confirmed using X-ray diffraction (XRD) and scanning electron microscopy (SEM). Theoretical predicted results (Halpin-Tsai model) are well below the experimental findings, especially at lower concentrations. Only at maximum concentrations, the experimental and theoretical results coincide. The high aspect ratio of MoS2 nanosheets, homogeneous dispersion inside polymer, and their probable planar orientation are the possible reasons for the effective stress transfer, resulting in enhanced mechanical characteristics. Moreover, the micro-Vickers hardness () of the MoS2-PS is also improved from 19 (PS) to 23 (0.002 MoS2-PS) as MoS2 nanosheets inclusion may hinder the deformation more effectively.