Yunjun Luo

Application of photoluminescent CdS/PAMAM nanocomposites in fingerprint detection.

Uniform and well-dispersed photoluminescent semiconductor CdS (cadmium sulfide) QDs (quantum dots) were in situ prepared inside Generation 4.0-NH(2) PAMAM (polyamidoamine) dendrimers in methanol, methanol and water mixed solutions of volume ratio 1:9, respectively. The prepared solutions containing photoluminescent semiconductor CdS QDs were utilized for detection of cyanoacrylate ester fumed fingerprints on tinfoil. The results show that fumed latent fingerprints treated with prepared CdS/PAMAM nanocomposites in methanol, 1:9 methanol:water mixed solutions emit pale yellow-green and orange luminescence respectively under ultraviolet excitation of 365 nm from an UV LED. Fumed fingerprints were successfully detected with good resolving rate and the mechanism was studied in detail.

Preparation and characterization of graphene aerogel/Fe2O3/ammonium perchlorate nanostructured energetic composite

A novel graphene aerogel (GA)/ferric oxide (Fe2O3)/ammonium perchlorate (AP) nanostructured energetic composite was prepared by a facile sol–gel method and supercritical carbon dioxide drying technique. In this study, the morphology and structure of the obtained GA/Fe2O3/AP nanostructured energetic composite were characterized by scanning electron microscopy, nitrogen sorption tests and X-ray diffraction. The thermal decomposition characteristic was investigated by thermogravimetry and differential scanning calorimetry. The results demonstrated that Fe2O3 and AP dispersed in the as-prepared energetic composite at nanometer, showing promising catalytic effects for the thermal decomposition of AP. For the nanostructured energetic composite, GA and Fe2O3 played a catalytic role in the thermal decomposition of AP. Only one decomposition step was observed, instead of two, which was common in previous report. The decomposition temperature of the nanocomposite was obviously decreased as well. Moreover, the total heat release increased significantly. The experimental results showed that the as-prepared GA/Fe2O3/AP nanostructured energetic composite could be a promising candidate material for the solid propellants.Graphical AbstractA novel GA/Fe2O3/AP nanostructured energetic composite was prepared by a facile sol–gel method and supercritical carbon dioxide drying technique. Fe2O3 and AP nanoparticles are added and trapped in the porous three-dimensional networks of GA. The decomposition temperature of the nanocomposite was obviously decreased, and the total heat release increased significantly. Moreover, the thermal decomposition mechanism of the nanocomposite was analyzed.

Graphene/nickel aerogel: an effective catalyst for the thermal decomposition of ammonium perchlorate

We report a simple and effective approach to fabricate graphene/nickel (G/Ni) aerogels by a sol–gel method and supercritical CO2 drying technique. The crystalline structure and chemical composition of the G/Ni aerogels have been investigated using X-ray diffraction and X-ray photoelectron spectroscopy. The morphology and porous attributes of the G/Ni aerogels have been characterized by transmission electron microscopy, scanning electron microscopy and nitrogen adsorption tests. Results indicate that the resulting aerogels, in which the Ni nanoparticles are dispersed on the graphene sheets, exhibit mesoporous structure and large surface areas. The catalysis effect of the G/Ni aerogels on the thermal decomposition of ammonium perchlorate was studied by differential scanning calorimetry. When 9 wt% of the aerogels was added, the thermal decomposition temperature of ammonium perchlorate was decreased by 122 °C. The results show that the G/Ni aerogels exhibit a remarkable catalytic performance for the thermal decomposition of ammonium perchlorate due to the combination of Ni nanoparticles and graphene sheets.

Energetic hybrid polymer network (EHPN) through facile sequential polyurethane curation based on the reactivity differences between glycidyl azide polymer and hydroxyl terminated polybutadiene

To improve the thermo-mechanical properties of glycidyl azide polymer (GAP) and hydroxyl terminated polybutadiene (HTPB) based propellants, a facile sequential polymerization approach has been conducted to prepare an energetic hybrid polymer network (EHPN) through stepwise curation. The detailed curing conditions for the EHPN formation were determined using an in situ FTIR kinetic study. The effect of curing ratio (NCO/OH) on the mechanical properties of the polyurethane networks of GAP and HTPB was investigated, wherein hexamethylene diisocyanate biuret trimer (Desmodur N100) and isophorone diisocyanate (IPDI) were used as mixed curative agents. A series of EHPNs were prepared by varying the relative weight ratios of GAP and HTPB with a single poly-isocyanate mixed curing system (IPDI/N100). A remarkable mechanical strength of up to 5.83 MPa and an elongation at break of 359% were achieved with a 50:50 weight ratio of GAP to HTPB, which is the maximum mechanical strength reported thus far for a binder system of GAP and HTPB, which has a thermally more stable cross-linked network. The thermal properties of the as-synthesized PU networks of GAP, HTPB and GAP–HTPB EHPNs with different weight ratios were characterized using the DMA and DSC techniques. Thermal degradation behavior and morphological studies were also investigated with TGA-DTG and scanning electron microscopy (SEM), respectively. The facile sequential polyurethane curation polymerization technique can be potentially used for advanced solid composite propellants.

Research on structures, mechanical properties, and mechanical responses of TKX-50 and TKX-50 based PBX with molecular dynamics

AbstractTo improve the practicality and safety of a novel explosive dihydroxylamm onium 5,5′-bis (tetrazole)-1,1′-diolate (TKX-50), polyvinylidene difluoride (PVDF) and polychlorotrifluoroe-thylene (PCTFE) were respectively added to the TKX-50, forming the polymer-bonded explosives (PBX). Interfacial and mechanical properties of PBX were investigated through molecular dynamics (MD) method, desensitizing mechanisms of fluorine-polymers for TKX-50 were researched by compression and bulk shear simulations. Results show that the binding energies (Ebind) between polymers (PVDF or PCTFE) and TKX-50 surfaces all rank in order of (011) > (100) > (010), shorter interatomic distance and the resulted higher potentials lead to higher Ebind on TKX-50/PVDF interfaces than that on PCTFE/TKX-50 interfaces. Compared with TKX-50, the ductility of PBX is improved due to the isotropic mechanical property and flexibility of fluorine-polymers especially the PCTFE. Desensitizing effect of fluorine-polymers for TKX-50 is found under loading condition, which is attributed to the enhanced compressibility and buffer capacity against external pressure in compression, as well as the improved lubricity to reduce the sliding potentials in bulk shear process. Graphical AbstractComparisons of the internal stress and slide potentials of the novel explosive,TKX-50 and its based PBX. Desensitizing effects can be found by the adding of fluorine-polymers, it owes to their better flexibility and lubricity as well as the amorphous nature.

Different catalytic systems on hydroxyl-terminated GAP and PET with poly-isocyanate: Curing kinetics study using dynamic in situ IR spectroscopy

ABSTRACT Reactions of hydroxyl-terminated glycidyl azide polymer (GAP) or poly(ethylene oxide-co-tetrahydrofuran) (PET) polymers with poly-isocyanate (N100) were monitored by dynamic in situ Fourier transform infrared spectroscopy. The influence of catalytic systems on the cure kinetics of polyurethane reaction was investigated. From the comparison between GAP/N100 and PET/N100 systems, it was found that primary and secondary hydroxyl groups were differentiated due to the effects of steric hindrance. Using Arrhenius law and Eyring equation, the activation parameters of polyurethane reaction were calculated at different catalytic systems. The negative value of the activation entropy demonstrated an associative mechanism within the transition state.

Synthesis and Characterization of Multifunctional Two-Component Waterborne Polyurethane Coatings: Fluorescence, Thermostability and Flame Retardancy

Fluorescent and flame-retardant two-component waterborne polyurethane coatings were synthesized using 1,5-dihydroxy naphthalene, a halogen-free polyphosphate and a hydrophilic curing agent, and their properties were systematically characterized. The average particle sizes and zeta potential values were below 170 nm and −30 mV. Meanwhile, the multifunctional two-component waterborne polyurethane coatings had strong fluorescence intensities. When comparing with the coatings with 0.5 wt % 1,5-dihydroxy naphthalene, the coatings with 1.0 wt % 1,5-dihydroxy naphthalene had a stronger microphase separation. Interestingly, the thermostability of the multifunctional coatings was remarkably improved through 1.0 wt % 1,5-dihydroxy naphthalene, and besides it belonged to nonflammable materials. Additionally, all of the coating films passed the solvent resistance testing. These samples with different amounts of 1,5-dihydroxy naphthalene are environmental friendly, especially applications that require transparent and fluorescent coatings.

Performance and Kinetics Study of Self-Repairing Hydroxyl-Terminated Polybutadiene Binders Based on the Diels–Alder Reaction

Based on the Diels–Alder reaction and hydroxyl-terminated polybutadiene (HTPB) binders of solid propellants, two novel compounds—furfuryl-terminated polybutadiene (FTPB) and trifurfuryl propane (TFP)—were designed and synthesized, and their structures were characterized. A new kind of reversible Diels–Alder reaction system was formed by FTPB as main resin, N,N′-1,3-phenylenedimaleimide (PDMI) as curing agent and TFP as chain extender. The results showed that this system had good mechanical properties with a tensile strength of 1.76 MPa and a tensile strain of 284% after curing, and the repair efficiency of the crack was 88%. Therefore, it could be used as a novel binder of energetic materials such as solid propellant and PBX explosives to provide them with self-repairing characteristics and improve the reliability for application.

Preparation and curing behavior of high-stress solid propellant binder based on polydicyclopentadiene:

The ring-opening metathesis polymerization reaction of dicyclopentadiene (DCPD) was carried out using Grubbs first generation catalyst. Fourier transform infrared (FTIR), dynamic-thermo mechanical analysis (DMA), and Raman spectroscopy were used to investigate the curing behavior of this polymer. The FTIR results showed that DCPD had not cured completely and the polymers were composed of linear and cross-linked polydicyclopentadiene (PDCPD). The DMA test showed that the polymer possesses the glass transition temperature of linear PDCPD and cross-linked PDCPD, which had also proved the FTIR result. Furthermore, in order to explain the strange phenomenon that the band at 3004 cm−1 should have been detected in infrared spectrum, the Raman spectrum of PDCPD was applied to analyze the bonding mechanism of =C–H bond in the process of polymerization. Moreover, the real-time FTIR result cure formula showed that the cure degree increases first then constants trend with cure time of increasing, the cure degree reached the maximum value (96.76%) at 60°C for 192 h.

Effects of water on the ballistic performance of para-aramid fabrics: three different projectiles

In this paper, the effects of water on the ballistic performance of the para-aramid fabrics were investigated through three typical projectiles (1.1 g FSP, 9 mm FMJ and 7.62 mm TYPE51). Three different aramid fabrics made up of Taparan 629 fiber or Kevlar 129 fiber were shot by these projectiles in both dry and wet conditions according to ballistic limited velocity V50 testing method (MIL-STD-662 F). Pull-out testing, water absorption, static contact angle, and failure mode of the fabrics were performed to study the possible ballistic mechanisms. The results reveal that the V50 values of three aramid fabrics all decrease after immersion in water, even the fabric has been treated with water-repellent finishing. The V50 values of aramid fabrics in wet state is affected by water absorption of fabric, yarns friction and bullet types. And, the slippage of yarns is a dominant mechanisms affected on ballistic performance of aramid fabric in wet condition. The lower water absorption and higher friction between the yarns can improve the ballistic performance of aramid fabrics.