Santosh Kumar Yadav

Fouling-Tolerant Nanofibrous Polymer Membranes for Water Treatment

Nafion/polyvinylidene fluoride (PVDF) nanofibrous membranes with electrostatically negative charges on the fiber surface were fabricated via electrospinning with superior water permeability and antifouling behaviors in comparison with the conventional microfiltration membranes. The fiber diameter and the resultant pore size in the nanofibrous membranes were easily controlled through tailoring the properties of the electrospinning solutions. The electrospun Nafion/PVDF nanofibrous membranes revealed high porosities (>80%) and high densities of sulfonate groups on the membrane surface, leading to praiseworthy water permeability. Unexpectedly, the water permeability was observed as proportional to the fiber diameter and pore size in the membrane. The presence of sulfonate groups on the membrane improved the antifouling performance against negatively charged oily foulants.

PDMS/MWCNT nanocomposite actuators using silicone functionalized multiwalled carbon nanotubes via nitrene chemistry

We demonstrate that covalently functionalized multiwalled carbon nanotubes (MWCNT) with a silicone copolymer via nitrene chemistry can be used as efficient conductive fillers for silicone dielectric elastomer actuators. The MWCNTs were covalently functionalized with poly(azidopropylmethyl)-co-(dimethylsiloxane) (silicone-N3) bearing an azide group through a nitrene addition reaction. The incorporation of a small amount of the uniformly silicone grafted MWCNTs (silicone-g-MWCNTs) in silicone dielectric elastomer strongly enhanced the mechanical, dielectric, and electromechanical properties of the resulting nanocomposites. This reinforcing effect is attributed to the homogeneous dispersion of silicone-g-MWCNTs in the silicone elastomer matrix due to the large degree of compatibility between the matrix and the passivation layers of the functionalized MWCNT.

Mechanically robust biocomposite films of chitosan grafted carbon nanotubes via the [2 + 1] cycloaddition of nitrenes

Chitosan functionalized multiwalled carbon nanotubes (CS-MWCNTs) are prepared using the [2 + 1] cycloaddition of nitrenes to the π electron system of carbon nanotubes followed by an amidation reaction with chitosan. The analysis of transmission electron microscopy (TEM) micrographs suggests the presence of more than 14 nm of chitosan grafted onto the MWCNTs, and the covalent linkage of chitosan with the MWCNTs is confirmed from FTIR and Raman spectra, XPS and energy dispersive X-ray spectroscopy (EDS) elemental mapping. The grafting density calculated using thermogravimetric analysis was 1.8 chitosan chains per 1000 MWCNT carbons. The effectiveness of the biofunctionalized CS-MWCNTs as a reinforcing filler (3 wt%) in a chitosan polymer matrix was verified by the dramatic enhancement of the mechanical properties (the tensile strength of the composite is significantly increased to 81.3 MPa from 36.5 MPa for pure chitosan, the highest modulus was up to 4.4 GPa for the composite with 3 wt% CS-MWCNTs) with a high elongation-at-break. The interfacial bonding between the CS-MWCNTs and the chitosan matrix plays a crucial role in the enhancement of the physical performance of the MWCNT-based composites.

Simultaneous reduction and covalent grafting of polythiophene on graphene oxide sheets for excellent capacitance retention

Herein, we report room temperature reduction and covalent grafting of graphene oxide sheets by thiophene derivatives to produce pseudocapacitive electrodes, which are capable of delivering high capacitance (230 F g−1 at 1 mV s−1) and, most important, 100% cycling retention after 5000 cycles. Raman and FTIR spectroscopies confirmed the strong interaction of PTh with rGO in the PTh-g-rGO hybrids.

A simple chemical treatment for easy dispersion of carbon nanotubes in epoxy matrix for improving mechanical properties

Carbon nanotubes have considerable potential for use as reinforcements in high-performance polymer composites, but their large-scale application has been hindered by their poor processability. Here, we report an extremely simple and scalable method for the chemical treatment of single-wall carbon nanotubes (SWNTs) to enable easy dispersion in an epoxy matrix. The treatment involves stirring SWNTs in a concentrated solution of sodium hydroxide in ethanol. The chemicals used can be recovered and re-used. The treated SWNTs show greater ease of exfoliation into organic solvents without the need for high-intensity ultrasonic probe treatment. Raman spectroscopy shows that the treatment does not create any noticeable defects or functional groups on the SWNT walls. As a result of the treatment, the SWNTs could be dispersed in epoxy with minimal, low-power ultrasonic treatment. The resulting composites showed increased fracture toughness and tensile strength at SWNT loadings as low as 0.5 weight percent, when compared with neat epoxy. The enhancement in properties of the composites does not decrease with increased SWNT loading, implying that the SWNTs do not re-aggregate.

Toughening Anhydride-Cured Epoxy Resins Using Fatty Alkyl-Anhydride-Grafted Epoxidized Soybean Oil

The aim of this work is to develop a series of advanced biobased tougheners for thermosetting epoxy resins suitable for high-performance applications. These bio-rubber (BR) tougheners were prepared via a one-step chemical modification of epoxidized soybean oil using biobased hexanoic anhydride. To investigate their toughening performance, these BR tougheners were blended with diglycidyl ether of bisphenol A epoxy monomers at various weight fractions and cured with anhydride hardeners. Significant improvements in fracture toughness properties, as well as minimal reductions in glass transition temperature (Tg), were observed. When 20 wt % of a BR toughener was utilized, the critical stress intensity factor and critical strain energy release rate of a thermosetting matrix were enhanced by >200 and >500%, respectively, whereas the Tg was reduced by only 20 °C. The phase-separated domains were evenly dispersed across the fracture surfaces as observed through scanning electron microscopy and atomic force microscopy. Moreover, domain sizes were demonstrated to be tunable within the micrometer range by altering the toughener molecular structure and weight fractions. These BR tougheners demonstrate the possibility of achieving toughness while having the thermal properties of standard bisphenol epoxy thermosetting resins.