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Smart elastomeric hydrogels based on polyacrylamide containing ferrimagnetic nanoparticles of BaFe12O19 alone or a combination of BaFe12O19 and graphene oxide were synthesized. An improvised sample preparation technique was evolved to design actuators, where the hydrogel samples in rolls form were inserted into cut pieces of hard plastic sleeve in order to fabricate a lab-level actuator. The magneto-responsive actuation behaviour was measured by applying an external magnetic field with the help of a hand-held square type of NdFeB magnet. While the sample containing only 20 wt% BaFe12O19 exhibited only 15 mm deflection at threshold magnetic field of 28 mT, the deflection was significantly enhanced up to 23 mm for the sample containing 1 wt% GO and 20 wt% BaFe12O19 at a threshold magnetic field of 36.7 mT. Up to 20 wt% BaFe12O19, the hydrogels showed a heterogeneous dispersion of large-sized BaFe12O19 clusters and addition of a small percentage, e.g. 1% of GO resulted in significant improvement in the homogeneity of dispersion as well as reduction of the scale of the BaFe12O19 clusters. The saturation magnetization value of the hydrogels was also improved by 50–75% due to the addition of 1 wt% GO with 20 wt% BaFe12O19.

NiMoO4 nanorods of different properties were synthesized via facile and scalable hydrothermal route by varying the reaction time and temperature and the effect of synthesis parameters on their electrochemical performances was investigated. Optimization of the synthesis parameters was carried out based on the electrochemical performance. Experimental analysis revealed that NiMoO4 nanorods synthesized at 150 °C for 6 h showed optimum electrochemical performance with specific capacitance, as high as 594 Fg−1 at 1 Ag−1 current density due to greater mesoporous nature and optimum crystallinity index. NiMoO4//activated carbon asymmetric supercapacitor device was fabricated using the optimized NiMoO4 nanorods and characterized for the electrochemical performances. Specific capacitance of 66 Fg−1 was obtained for the fabricated supercapacitor device at 1 Ag−1 current density and 56% retention of the specific capacitance was observed after 1000 cycles. An energy density of 18 Whkg−1 and power density of 704 Wkg−1 were achieved at 1 Ag−1 current density which offer great promise for supercapacitor application of this material.

Microwave absorbing polymer composites are important for strategic applications in several defense systems for detection and/or deception purposes as well as for other industrial applications, where the enclosed electronic gadgets or human beings need shielding from electromagnetic radiations from the environment. The extent of absorption or reflection of the microwave by these composites, however, can be controlled by proper selection of type of constituting base polymers and reinforcement types, nature of different additives, crosslinking agents used in the polymer formulation, and also on the nature of fabrication of suitable structures, that is, by combination or layering of different constitutive components of the functionally gradient composites. Carbon, besides being an excellent dielectric and lightweight material, exists in various forms like carbon nanotubes, nanospheres, graphene, carbon black, nanofibers, hollow carbon nanostructures, etc. and many of these, especially the carbon nanofibers (CNFs), which are conventionally used as reinforcing fillers for development of polymer composites, are also found to be excellent microwave absorbers. In this chapter, the various formulations, fabrication, characterization of CNF-reinforced polymer nanocomposites for microwave absorption are given and the same are discussed in detail. Besides, the factors affecting the microwave absorption properties, effect of bandwidth on the extent of reflection loss and plausible mechanism of microwave absorption have also been described. Essentially, this recent investigations reported on the microwave absorption properties of nonmetallic advanced fiber-reinforced polymer composites establish the achievement of very effective microwave absorption in a broad frequency range, resulting in lightweight materials for thinnest possible structures.

The combined effect of both hollow, mesoporous structure of carbon nanofiber and Fe3O4 nanoparticles on the microwave absorption properties of polydimethylsiloxane nanocomposites have been investigated. Nanofibers with above characteristics were prepared via coelectrospinning the solutions of polyacrylonitrile/FeCl3 and poly(methyl methacrylate) followed by stabilization and carbonization at elevated temperatures. Carbonized nanofibers contained Fe3O4 nanoparticles with average crystallite size of ∼12.3–14.6 nm and exhibited a surface area of 126.4–377.7 m2/g. Catalytic graphitization surrounding Fe3O4 nanoparticles was seen in high-resolution transmission electron microscopy and also supported by a decrease in intensity ratio of D to G bands in Raman spectra. Microwave absorption properties of nanocomposites were investigated in a vector network analyzer using a coaxial waveguide in the frequency range of 2–18 GHz and found to be dependent on thickness, filler loading, and Fe3O4 content of the nanofibers...

Hierarchical metal oxide nanostructures emerge as the promising candidate for energy storage application due to their huge surface area, porosity and interconnected electron transport pathways. In this article, we report for the first time the electrochemical properties of very uniform and efficient thorn apple fruit like nickel cobaltite nanostructures of different forms and investigated the structure-property relationship. NiCo2O4 is directly grown over the Ni-foam by a cheap, scalable and facile hydrothermal technique and characterized for structural, morphological and porous characteristics. Electrochemical properties are determined by conducting cyclic voltammetry, galvanostatic charge-discharge and electrochemical impedance analysis. The non-annealed NiCo2O4.nH2O possesses mesoporous nanostructure with pore size centering between 3 and 10 nm which being the optimum size enables the material to exhibit best electrochemical properties. Specific capacity reaches as high as 670C/g for NiCo2O4.nH2O at 0.5 A/g current density. Asymmetric supercapacitor device is fabricated by combining binder free cathode and activated carbon and investigated for device performance. Specific capacity, energy and power density as high as 129C/g, 55.9 Wh/kg and 751.4 W/kg are achieved at 0.5A/g current density with the fabricated device. The device exhibits 98% retention of specific capacity after 10,000 cycles demonstrating its potential for high energy durable supercapacitor application.

Development of magneto-sensitive smart hydrogels based on crosslinked polyacrylamide (PA) mixed with either nanoparticles of barium ferrite (BaM) or combinations of both BaM and graphene oxide (GO), as nanosheets, have been carried out. Spherical BaM particles with an average crystallite size of 46.63 nm were synthesized using an ultrasonic assisted novel coprecipitation method. Thin films of isotropic PA hydrogel nanocomposites were obtained by solution casting of in-situ polymerized mixture of acrylamide, N,N methylene bisacrylamide monomer (crosslinker) and a redox initiator and the fillers, as above. Variety of characterization techniques viz. , XRD, for determination of crystal structure of nanofillers; X-ray photoelectron spectroscopy, for determination of chemical composition and oxidation state of elements in BaM; FTIR, for interaction of BaM and GO with polymer matrix; DSC, for determination of glass transition temperature and FESEM and TEM, for correlation of morphological features with the magnetorheological (MR) properties were used. MR studies were conducted in a parallel plate rheometer and the composites were found to exhibit both negative and positive MR effects depending on concentration and dispersion of the fillers added to the polymer. High surface energy and permanent magnetization of the nanoparticles lead to formation of large clusters interconnected through bridges. The positive MR effect at very low concentration of BaM is attributed to the localized hardening of the polymer matrix by the heterogeneously dispersed BaM clusters. Addition of GO along with BaM improves further the dispersion of BaM nanoparticles but the negative MR effect still holds up to 10 wt% loading of BaM. However, increase in BaM loading to 20 wt% in presence of GO leads to a positive MR effect. This is due to higher concentration of BaM which formed a continuous network of nanoparticles and the shear stress could not break the connectivity between the nanoparticles resulting in a positive MR effect.

In this study, we present the actual electrochemical performance of a highly stable hybrid supercapacitor device based on faradic type binder free nickel ferrite (NiFe2O4) positive electrode and activated carbon negative electrode. NiFe2O4 nanoparticles are directly grown over the Ni-foam and stainless steel substrates by a scalable and novel surfactant assisted co-precipitation technique. The structural and morphological properties of the NiFe2O4 nanoparticles are investigated by using different characterization techniques. The electrochemical performance is investigated in 6 M aqueous KOH electrolyte using cyclic voltammetry and galvanostatic charge-discharge techniques. Ni-foam/NiFe2O4 positive electrode exhibits specific capacity of 398 C/g at 1 A/g current density which is much higher than the stainless steel /NiFe2O4 positive electrodes and can be attributed to the better interfacial bonding between Ni-foam and NiFe2O4 nanoparticles and formation of a concomitant 3D porous architecture. A maximum specific energy of 27.71 Wh/kg and specific power of 14.49 kW/kg are achieved at 1 and 20 A/g current density in the hybrid supercapacitor device fabricated utilizing the Ni-foam/ NiFe2O4 positive and activated carbon negetive electrodes. Moreover, the device shows ~98% retention of its specific capacity after 6500 cycles at 5 A/g current density which reveals superiority of NiFe2O4 as an electrode material for supercapacitor application.

We show for the first time the greatly enhanced magnetic and magnetorheological (MR) properties of CoFe2O4–silicone elastomer (cross-linked polydimethylsiloxane) composites containing electrospun CoFe2O4 nanofibers. The effects of CoFe2O4 particle shape (spherical to fibrous), concentration and degree of alignment in the elastomeric matrix are explored. Low nanofiber loadings (5–10 wt%) give MR properties comparable to those obtained by much higher microparticle additions (60–80 wt%) for the same polymer matrix. Compared to spherical nanoparticles, the nanofiber composites have 100–400% improvement in MR properties that are vital in tunable rheology applications such as vibration damping, variable stiffness devices, actuators, etc. The nanofibers effectively formed an interconnected network within the polymer matrix but nanoparticles exhibited large gaps between two disconnected short particle chains at lower filler loading. Spherical particles with 69.46 emu g−1 saturation magnetization were synthesized by ultrasonic assisted co-precipitation method using a novel precipitating solvent (i.e. propylamine) followed by calcination. The nanofibers were prepared by electrospinning a precursor of CoFe2O4 in a sacrificial polymer solution of polyvinylpyrrolydone (PVP) followed by calcination of electrospun fibers. Crystal structure and magnetic properties of the CoFe2O4 nanofillers were evaluated by X-ray diffraction (XRD), transmission electron microscopy (TEM) and vibrating sample magnetometery (VSM), which showed the generation of larger crystallite size with greater coercivity and remnant magnetization in the nanofibers compared to nanoparticles. Thin films of the nanocomposites containing nanoparticles and nanofibers were prepared with 5 and 10 wt% of CoFe2O4. Anisotropic characteristics of the nanocomposites were generated by applying an in situ magnetic field of 0.4 T during solution casting of thin composite films. The magnetorheological study revealed that at 1.023 T, the isotropic nanocomposites with 10 wt% nanofibers showed absolute and relative MR effects of 4.4 kPa and 3.21%, respectively, compared to the corresponding nanoparticle containing counterpart's values of 2.0 kPa and 0.64%.

We investigate for the first time the magnetorheological (MR) properties of bimetallic alloy nanocomposites based on cross-linked polydimethylsiloxane elastomer and ferromagnetic FeCo3 nanoparticles. The nanoparticles (∼30 nm), with a saturation magnetization value of 166 emu/g, are synthesized by hydrazine reduction of Fe2+ and Co2+ metal ions. Isotropic and anisotropic nanocomposite films are prepared by a solution casting technique with 5, 10, and 20 wt % FeCo3 in the absence and presence of 0.2 T magnetic field, respectively. The structural, morphological, and magnetic properties of nanoparticles and their composites are characterized by X-ray diffraction, transmission electron microscopy, field emission scanning electron microscopy, confocal and optical microscopy, and vibrating sample magnetometer analysis. Steady-state and dynamic mechanical properties of the nanocomposite under a magnetic field are evaluated by rotary shear, strain amplitude sweep, angular frequency sweep, and magnetic flux densit...

This study for the first time evaluated quantitatively the effect of carbon nanofibre (CNF) reinforcement on tribological properties of epoxy nanocomposites. Nanocomposites containing 0.0, 0.5, 1.0, 1.5, 2.0, 2.5 and 3.0 wt% CNF were fabricated by casting technique after dispersing CNFs in epoxy resin by ultrasonication and mechanical stirring. Sliding and abrasive wear were investigated using a pin-on-disc apparatus and evaluated statistically for the effect of CNF reinforcement by one-way ANOVA. Sliding wear test revealed that CNF content significantly affected specific wear rate but not frictional coefficient. Reinforcement with 0.5 to 2.5 wt% CNF reduced the specific wear rate compared to the control (neat epoxy). However, specific wear rate was increased at 3.0 wt% CNF. Abrasive wear test showed that CNF reinforcement causes numerical decrease in wear rate but the effect was statistically non-significant. Surface morphology was investigated by SEM to obtain the possible wear mechanism of the nanocomposites.

The poly(ether ether ketone) micro/nanocomposite reinforced with N-(2-aminoethyl)-3-aminopropyl triethoxy silane treated micro- and nano-sized nickel and zirconia (0.5, 1, and 3 wt%) were prepared by melt mixing in a co-rotating twin screw extruder followed by test specimen fabrication in microinjection molding. The resulting nanocomposites with 3 wt% Ni and ZrO2 nanoparticles exhibit the maximum improvement in tensile and flexural strength as well as the modulus with respect to neat poly(ether ether ketone). The lowest specific wear rate of 17.6 × 10−4 mm3/N/m has been achieved with 3 wt% nano-Ni-filled composite in comparison to neat poly(ether ether ketone)’s value 191.5 × 10−4 mm3/N/m. The thermal stability of micro- and nano-particle reinforced poly(ether ether ketone) composites measured by thermogravimetric analysis found to be higher than the unfilled poly(ether ether ketone).