Facile Solution Process of VO2 Film with Mesh Morphology for Enhanced Thermochromic Performance

The fabrication and applications of VO2 film continue to be of considerable interest due to their good thermochromic performance for smart windows. However, low visible transmittance (Tlum) and solar modulation efficiency (∆Tsol) impede the application of VO2 film, and they are difficult to improve simultaneously. Here, a facile zinc solution process was employed to control the surface structure of dense VO2 film and the processed VO2 film showed enhanced visible transmittance and solar modulation efficiency, which were increased by 7.5% and 9.5%, respectively, compared with unprocessed VO2 film. This process facilitated the growth of layered basic zinc acetate (LBZA) nanosheets to form mesh morphology on the surface of VO2 film, where LBZA nanosheets enhance the visible transmittance as an anti-reflection film. The mesh morphology also strengthened the solar modulation efficiency with small caves between nanosheets by multiplying the times of reflection. By increasing the zinc concentration from 0.05 mol/L to 0.20 mol/L, there were more LBZA nanosheets on the surface of the VO2 film, leading to an increase in the solar/near-infrared modulation efficiency. Therefore, this work revealed the relationship between the solution process, surface structure, and optical properties, and thus can provide a new method to prepare VO2 composite film with desirable performance for applications in smart windows

Molecular Dynamics of Neutral Polymer Bonding Agent (NPBA) as Revealed by Solid-State NMR Spectroscopy

Neutral polymer bonding agent (NPBA) is one of the most promising polymeric materials, widely used in nitrate ester plasticized polyether (NEPE) propellant as bonding agent. The structure and dynamics of NPBA under different conditions of temperatures and sample processing are comprehensively investigated by solid state NMR (SSNMR). The results indicate that both the main chain and side chain of NPBA are quite rigid below its glass transition temperature (Tg). In contrast, above the Tg, the main chain remains relatively immobilized, while the side chains become highly flexible, which presumably weakens the interaction between bonding agent and the binder or oxidant fillers and in turn destabilizes the high modulus layer formed around the oxidant fillers. In addition, no obvious variation is found for the microstructure of NPBA upon aging treatment or soaking with acetone. These experimental results provide useful insights for understanding the structural properties of NPBA and its interaction with other constituents of solid composite propellants under different processing and working conditions.National Natural Science Foundation (China) (21120102038)National Natural Science Foundation (China) (21373265)National Natural Science Foundation (China) (21003154

Thermodynamic Simulation of the RDX-Aluminum Interface Using ReaxFF Molecular Dynamics

We use reactive molecular dynamics (RMD) simulations to study the interface between cyclotrimethylene trinitramine (RDX) and aluminum (Al) with different oxide layers to elucidate the effect of nanosized Al on thermal decomposition of RDX. A published ReaxFF force field for C/H/N/O elements was retrained to incorporate Al interactions and then used in RMD simulations to characterize compound energetic materials. We find that the predicted adsorption energies for RDX on the Al(111) surface and the apparent activation energies of RDX and RDX/Al are in agreement with ab initio calculations. The Al(111) surface-assisted decomposition of RDX occurs spontaneously without potential barriers, but the decomposition rate becomes slow when compared with that for RDX powder. We also find that the Al(111) surface with an oxide layer (Al oxide) slightly increases the potential barriers for decomposition of RDX molecules, while α-Al_2O_3(0001) retards thermal decomposition of RDX, due to the changes in thermal decomposition kinetics. The most likely mechanism for the thermal decomposition of RDX powder is described by the Avrami–Erofeev equation, with n = 3/4, as random nucleation and subsequent growth model. Although the decomposition mechanism of RDX molecules in the RDX/Al matrix complies with three-dimensional diffusion, Jander’s equation for RDX(210)/Al oxide and the Zhuralev–Lesokin–Tempelman (Z-L-T) equation for RDX(210)/Al_2O_3(0001) provide a more accurate description. We conclude that the origin of these differences in dynamic behavior is due to the variations in the oxide layer morphologies

Ultrasound irradiation in the production of ethanol from biomass

Ethanol produced from renewable biomass, such as lignocellulosic feedstock, is one of the alternative energy resources that can be environmentally friendly. However, physical and chemical barriers caused by the close association of the main components of lignocellulosic biomass, as well as starch, hinder the hydrolysis of cellulose and hemicellulose in lignocellulose as well as amylase and amylopectin in starch to fermentable sugars. One of the main goals of pretreatment for enzymatic hydrolysis is to increase the enzyme accessibility for improving digestibility of cellulose and starch. Ultrasound irradiation applied to cellulosic materials and starch-based feedstock was found to enhance the efficiency of hydrolysis and subsequently increase the sugar yield. Prior research conducted on applying ultrasonic technology for cellulose and starch pretreatment has considered a variety of effects on physical and chemical characteristics, hydrolysis efficiency and ethanol yield. This paper reviews the application of ultrasound irradiation to cellulose and starch prior to and during hydrolysis in terms of sugar and ethanol yields. It also addresses characteristics such as accessibility, crystallinity, degree of polymerization, morphological structure, swelling power, particle size and viscosity as influenced by ultrasonic treatment. © 2014 Elsevier Ltd

Uniaxial tensile mechanical behavior research of HTPB propellant under wide temperature and confining pressure

To investigate the effects of confining pressure, strain rates, and temperatures on the mechanical properties of the Hydroxyl-terminated Polybutadiene (HTPB) propellant, uniaxial tensile tests were performed utilizing wide-temperature-confining pressure systems. The resulting damage was subsequently analyzed and characterized through scanning electron microscopy and mirco-ct. The results indicate that the stress–strain curves of HTPB at 20 and 70 °C are comparable, and the propellant damage is primarily attributed to de-wetting at 20 and 70 °C with respect to the mechanism. At −50 °C, the maximum tensile strength and ultimate tensile strain at 8 MPa surpass those at 0 and 2 MPa to a significant degree and the damage shifts from de-wetting and ductile fracture of particles to severe particle breakage with the elevated confining pressure. Ultimately, the primary curve of the HTPB propellant's maximum tensile strength was constructed by the curve fitting analysis based on the time–temperature equivalent superposition principle (TTSP) and time–pressure equivalent superposition principle (TPSP). Comparing to the properties of TPSP, TTSP exhibits a wider range of applicability and greater fitting precision in relation to the HTPB propellant. This study mainly serves to establish a fundamental theory and furnish data support for the enhancement of mechanical properties and structural integrity of solid rocket motors

Dual-Functionalized Imidazolium Ionic Liquids as Curing Agents for Epoxy Resins

As epoxy resin curing agents, ionic liquids can help improve mechanical properties, flame retardancy, and wear and tear self-healing and extend the pot life of epoxy compositions. The functional design of ionic-liquid curing agents may significantly improve the overall performance of epoxy resins. In this paper, a series of dual-functionalized ionic liquids, e.g., 1-(3-amino-3-oxopropyl)-3-propynyl-imidazolium, 1-(3-amino-3-oxopropyl)-3-(2-amino-2-oxoethyl)-imidazolium, and 1-allyl-3-(2-amino-2-oxoethyl)-imidazolium combined with dicyanamide (N(CN)(2)(-)) or bis(trifluoromethylsulfonyl)imide (NTf2-) anions, were synthesized and characterized as curing agents for diglycidyl-4,5-epoxy-cyclohexane-1,2-dicarboxylate (TDE-85). medium or high-temperature curing agents for TDE-85 with the curing temperature The results showed that the obtained bifunctional ionic liquids can be used as a range of 130-208 degrees C and the best mass ratio range of 15:100-40:100. Thermosets obtained from the bifunctional ionic liquid and TDE-85 curing system exhibit better heat resistance with the glass transition temperature of 187-212 degrees C and the decomposition temperature at 10% weight loss of 282-357 degrees C. The curing reaction mechanism of the 1-(3-amino-3-oxopropyl)-3-(2-amino-2-oxoethyl)-imidazolium NTf2-/TDE-85 system mainly has three processes

Study on Mechanical Properties of Polyurethane Cross-Linked P(E-co-T)/PEG Blended Polyether Elastomer

To improve the mechanical properties of polyurethane cross-linked poly (ethylene oxide-co-tetrahydrofuran) (P(E-co-T)) elastomers at room temperature, using poly (ethylene oxide-co-tetrahydrofuran) and high-molecular-weight polyethylene glycol (PEG) as raw materials and polyisocyanate N100 as curing agent, a series of polyurethane cross-linked blended polyether elastomers were prepared by changing the elastomer-curing parameter R value (n(-NCO)/n(-OH)) and P(E-co-T)/PEG ratio. Equilibrium swelling measurements showed that the chemical cross-linkage of the elastomers tended to decrease with the decreasing R value, the average molecular weight (Mc) of the network chain increased, and the density of the network chain (N0) decreased. Wide-angle X-ray diffraction (WAXD) and differential scanning calorimetry (DSC) tests showed that PEG chain segments within the elastomers crystallized at room temperature, while the crystallinity increased with decreasing R value and increasing PEG content. The mechanical property tests showed that the elongation at break tended to decrease with increasing R value; the tensile strength first increased and then decreased. At R value 0.9, the elastomer presented good comprehensive mechanical properties. In addition, the mechanical properties of polyurethane cross-linked P(E-co-T)/PEG blended polyether elastomer showed an increasing trend with the increase in PEG content when the curing parameter of 0.9 remained unchanged

Molecular Dynamics of Neutral Polymer Bonding Agent (NPBA) as Revealed by Solid-State NMR Spectroscopy

Neutral polymer bonding agent (NPBA) is one of the most promising polymeric materials, widely used in nitrate ester plasticized polyether (NEPE) propellant as bonding agent. The structure and dynamics of NPBA under different conditions of temperatures and sample processing are comprehensively investigated by solid state NMR (SSNMR). The results indicate that both the main chain and side chain of NPBA are quite rigid below its glass transition temperature (Tg). In contrast, above the Tg, the main chain remains relatively immobilized, while the side chains become highly flexible, which presumably weakens the interaction between bonding agent and the binder or oxidant fillers and in turn destabilizes the high modulus layer formed around the oxidant fillers. In addition, no obvious variation is found for the microstructure of NPBA upon aging treatment or soaking with acetone. These experimental results provide useful insights for understanding the structural properties of NPBA and its interaction with other constituents of solid composite propellants under different processing and working conditions

Combustion characteristics of cross-linked fluorinated polymer supported aluminum/oxidizer microsphere in HTPB propellant

Combustion behaviors of propellant depend heavily on the architecture of the pocket bounded by coarse AP particles. In order to achieve a better control of the meso-scale architecture of the pocket, overcoming random mixing of the fine particles inside propellant, two kinds of cross-linked fluorinated polymer supported Aluminum/Oxidizer microspheres containing fine Al and oxidizer particles are fabricated by emulsion solvent evaporation and in-situ polymerization method (ESV-ISP), which are used to replace the fine Al and oxidizer particles of the Al/AP/HMX/HTPB propellant. The morphologies of the Al/Oxidizer microspheres and the corresponding propellants are studied, it shows that the fine Al and oxidizer particles are well dispersed and arranged in the microspheres. Besides, the average sizes of the microspheres are ranging from 113.9 ± 4.3 μm to 183.0 ± 5.9 μm, and equivalent to that of the Al-rich clusters located inside the pocket. The energy property and combustion performance of the propellants indicated that the combustion heat of the propellants containing Al/Oxidizer microsphere is increased by about 200 J/g, while the fraction of residual active aluminum is decreased by 77.8%, additionally, the D50 and D(4,3) of the combustion residue are both reduced significantly. Large Al aggregate nearby the burning surface is observed clearly in the blank propellant, while it could not be observed in the propellants containing Al/Oxidizer microsphere. Furthermore, compared to the pressure exponent (n), 0.34, of the B-Propellant, the n of the Al/AP-Propellant and the Al/HMX-Propellant significantly drop to 0.24 and 0.25, respectively, and the burning rate (r) could be adjusted and controlled by the Al/Oxidizer microsphere consisting of different fine oxidizer particles. It demonstrates that using the structurally ordered Al/Oxidizer microsphere could successfully achieve a better control of the meso-scale architecture of the pocket in typical Al/AP/HMX/HTPB propellant