Rahim Jan

The present work is on the synthesis and investigation of the structural, optical, and optoelectrical properties of NbSe₂ as an efficient material for energy conversion applications. The liquid phase exfoliation method was employed for the synthesis of 2D nanosheets from the bulk NbSe₂ at different exfoliation levels. SEM was used to confirm the physical dimensions of the nanosheets, while XRD was used to verify the structural retention of hexagonal nanosheets. The results demonstrate that high-quality, single-crystalline NbSe₂ nanosheets with a size of ≈1 μm in the lateral dimension and ≈6–12 nm thick were obtained. The 2D nanosheets will be further explored for energy storage and conversion applications.

Liquid exfoliated, 2-dimensional (2D), few layered graphene and molybdenum disulfide nanosheets (GNS and MNS) are size selected for EMI shielding application. Scanning electron microscopy (SEM) has confirmed the lateral dimensions increase (1–2 µm for GNS and MNS) with lowering centrifugation speed (1000 to 500 rpm). The micron size (~ 15 µm) restacked structures of GNS and MNS (L ~ 2 µm) over a nylon membrane have shown ~ 16 dB and ~ 6 dB EMI shielding effectiveness (1–8 GHz frequency), respectively. The enhanced EMI shielding effectiveness for GNS-500 may be credited to its high carrier mobility as well as high aspect ratio of nanosheets. The GNS-500 are further dispersed (0.3 wt.%) in thermoplastic polyurethane for their applicability as flexible EMI shielding material. The dielectric characteristics predicted an enhancement for the attenuation (200 MHz–1 GHz). The experimental results (1–8 GHz) suggested the maximum attenuation ~ 18 dB showing the composite applicability as a broadband EMI shielding material.

Hybrid polymer composites based on poly vinylidene fluoride (PVDF) matrix are fabricated by dispersion of few layered graphene (FLG) and nickel spinal ferrites (NSF) for improving EMI shielding effectiveness. The FLG loading is kept constant at 3 wt% while NSF content is varied from 15–30 wt% in PVDF using solution processing technique. The shielding effectiveness in the frequency domain of 1–12 GHz is enhanced ranging 25 dB–45 dB for PVDF/FLG composite as compared to ∼0 dB for neat PVDF. With addition of NSF up to 15 wt%, the attenuation is increased to 30 dB–53 dB, clearly indicating the effective interaction and network formation of FLG and NSF in PVDF matrix. Moreover, the shielding effectiveness trend is reduced to 12 dB–43 dB as the NSF loading is increased to 30 wt% owing to its agglomeration. Absorption is the dominant phenomena in obtaining the total shielding effectiveness of ∼53 dB for PVDF/FLG-3 wt%NSF-15 wt% hybrid polymer composites. Additionally, the I-V curves provide the electrical conductivity trend while scanning electron microscope (SEM) confirms the network formation in hybrid composite.

Suspensions comprises of gold nanostructures deposited on a number of alternating hydrophilic silicon dioxide (SiO2) and hydrophobic perfluorodecyltrichlorosilane (PFDTS) stripe patterned surfaces via droplet evaporation technique. On such surfaces during evaporation of aqueous phase, three-phased contact line of a droplet deposit nanoparticles preferentially on the hydrophilic set of stripes and consequently leads to the formation of nanoparticles patterning over the substrate. The presence of the hydrophobic stripes on both sides of the SiO2 stripe on such patterned substrates will push the liquid towards the hydrophilic stripe which will induce hydrodynamic confinement effect. Such hydrodynamic confinement will help to produce nanoparticle patterns that will merely decorate hydrophilic set of stripes with gold nanorod deposits. Near the interfaces, aligned arrays of gold nanorods are observed whereas in some locations within the deposits ribbon-like arrays are observed. In case of citrate-stabilized gold nanospheres (diameter~10nm), bonding sites for nanospheres on the hydrophilic stripes are provided by self-assembled monolayers of 3-triethoxysilylpropylamine (APTES). The presence of APTES will facilitate gold nanoparticles deposition (monolayer) on the hydrophilic set of stripes whereas hydrophobic stripes display agglomerated and mobilized bunches of nanoparticles. As such nanoparticle clusters are unstable on the PFDTS surface, hence can be removed by applying air blowing mechanism. Air rushing across the substrate nearly removes all nanoparticles on the hydrophobic stripes whereas particle arrangement on the hydrophilic region remains unaltered.

Liquid exfoliated molybdenum disulfide (MoS₂) nanosheets and polyaniline (PANI) nanoparticles are dispersed in polystyrene (PS) matrix to fabricate hybrid polymer composites with high dielectric and electromagnetic interference (EMI) shielding behavior. A phase-separated morphology is formed when PANI and MoS₂ are incorporated into polystyrene (PS) matrix. An increasing concentration of MoS₂ nanoparticles inside PS/PANI (5 wt %) polymer blend forms an interconnected network, resulting in high electrical conductivity and dielectric behavior, making them a suitable candidate for EMI shielding application. An increment in dielectric constant and loss, up to four and five orders of magnitude, respectively, is recorded at a maximum concentration of 1 wt % of MoS₂ in PS/PANI-5 polymer blend at 100 Hz. The enhanced dielectric characteristics for PS/PANI/MoS₂ composites are then theoretically evaluated for the estimation of EMI shielding effectiveness in the frequency range of 100 Hz to 5 MHz. The maximum dielectric constant and loss achieved for PS/PANI-5 wt %/MoS₂-1 wt % are responsible for estimated shielding effectiveness of around 92 dB at 100 Hz. The increase in dielectric behavior and shielding effectiveness is probably due to the increased number of charged dipoles accumulated at the insulator–conductor interface.