RESUMO
There are several chemical methods for the synthesis of high energy-density fuel, exotetrahydrodicyclopentadiene (exo-THDCPD), however, still there is a challenge to synthesize exo-THDCPD conveniently. In present work, the exo-THDCPD from dicyclopentadiene (DCPD) has successfully synthesized through simplest and greener single step hydroconversion reaction over mesoporous supported nickel nanocatalyst (Ni/MCM-41). The reaction performed in autoclave under a hydrogen pressure ranging from 300-400 (Psi), temperature range 130-150 °C and progress has been monitored by gas chromatography which reveals that the reaction mechanism goes through dissociation-recombination of DCPD. The major reaction parameters such as temperature, pressure and nanocatalyst have been experimentally examined for the yield (85%) of the product. The structural analysis of exo-THDCPD is carried out by 1H NMR and FTIR techniques and the physicochemical properties have also been evaluated. Good quality nanocatalyst Ni/MCM-41 has been synthesized by impregnation incipient wetness method and characterized by XRD, EDAX, TEM, and BET techniques. The nanocatalyst is highly reactive due to its mesoporous structure having appropriate size and shape which gives free diffusion of the molecules. Repeatability of the nanocatalyst shows good reactivity up to the four runs.
RESUMO
Herein, we report a novel nanosilica-based shear-thickening fluid, whose shear-thickening performance has been largely augmented by surface functionalizing silica employing silane chains. The functionalized shear-thickening colloids were transparent; this suggested that they have promise for application. An enhancement in viscosity was observed by over an order of magnitude by the usage of functionalized particles, which could be explained on the basis of enhanced hydroclustering and an order-to-disorder transition of the particles due to physical bonding of the silane with the base polymer. It was also observed that the shear-thickening behavior was grossly modified due to the presence of the functionalized nanoparticles. Oscillatory analysis showed that the functionalized colloids exhibited an improved dynamic response, with enhanced elastic behavior under variant strain and frequency conditions. Additionally, impact resistance tests revealed that the thickening of the viscosity upon impact was augmented by over an order of magnitude; this established these functionalized colloids as excellent candidates for liquid armors. The viscoelastic behavior was modeled based on the Cox-Merz formalism. Additionally, three-element viscoelastic modeling was performed, and it was observed that while the silica-based colloids conformed to the predominantly viscous model, the functionalized system transited to a predominantly elastic model. The present article can have important implications for the design and engineering of shear-thickening fluids employing nanomaterials.
RESUMO
Magnetic nanocolloids consisting of synthesized superparamagnetic iron(II,III) oxide nanoparticles (SPION) (5-15 nm) dispersed in poly(ethylene glycol) (PEG) and a nano-silica complex have been synthesized. The PEG-nano-silica complex physically encapsulates the SPIONs, ensuring that there is no phase separation under high magnetic fields (â¼1.2 T). Exhaustive magneto-rheological investigations have been performed to understand the structural behavior and response of the ferrocolloids. Remarkable stability and reversibility have been observed under magnetic field for concentrated systems. The results show the impact of particle concentration, size and encapsulation efficiency on parameters such as shear viscosity, yield stress, viscoelastic moduli, magneto-viscous hysteresis, and so on. Analytical models to reveal the system mechanism and mathematically predict the magneto-viscosity and magneto-yield stress have been developed. The mechanistic approach based on near-field magnetostatics and Néel-Brownian interactivities could predict the colloidal properties under the effect of the magnetic field accurately. The colloid exhibits amplified storage and loss moduli together with a highly augmented linear viscoelastic region under magnetic stimuli. The transition of the colloidal state from the fluidic phase to the soft condensed phase and its viscoelastic stimuli under the influence of a magnetic field has been explained based on the mathematical analysis. The remarkable stability, magnetic properties and accurate physical models reveal promise for the colloids in transient situations, namely, magneto-microelectromechanical/nanoelectromechanical devices, anti-seismic damping, biomedical invasive treatments, and so on.
