Strong Van Der Waals Forces Research Articles

A CFD‐DEM study of the solid‐like and fluid‐like states in the homogeneous fluidization regime of Geldart A particles

AbstractThe mechanisms underlying homogeneous fluidization of Geldart A particles have long been debated. Recent experiments shed fresh insights that both a solid‐like and a fluid‐like state exist. Herein, 3D computational fluid dynamics‐discrete element method simulations with the incorporation of interparticle van der Waals forces were performed for five typical Geldart A particles to investigate the bed structure in the homogeneous fluidization regime. Simulation results reproduce the existence of the solid‐like and fluid‐like states, showing that in the solid‐like state, particles have enduring and strong interparticle van der Waals forces that stabilize the bed to keep the bed stationary; while in the fluid‐like state, the interparticle van der Waals forces are dominated by the drag force, and particles show global circulation. Both interparticle van der Waals forces and friction are found to be necessary for the existence of the solid‐like state, and increasing the former has an effect to widen the solid‐like state.

Rate dependent adhesion of nanoscale polymer contacts

The adhesive interactions between polymer nanofibers strongly influence the mechanical behavior of their networks in synthetic materials and biological systems. A treatment of the adhesive interactions at polymer contacts must take into account the viscoelastic behavior of the material in the contact region and the associated energy dissipation. This study focuses on the rate-dependent adhesion of polyacrylonitrile (PAN) nanofibers which interact with strong van der Waals forces. Experimental measurements of the detachment force between PAN fibers with diameters 400 and 4000 nm showed that the apparent work of adhesion increases with the rate of unloading by a factor of two within a three orders of magnitude increase in the unloading rate. In order to obtain further insights into this rate-dependent adhesion, the Maugis-Dugdale (M-D) elastic contact model for normal detachment was extended to include a linear viscoelastic behavior of the PAN nanofibers. The extended model predicted the normal pull-off force instabilities in good agreement with the experiments, capturing well the effect of the unloading rate. The calculated viscoelastic time constants were of the order of milliseconds, suggesting fast relaxations in the contact region, which explain the instantaneous full-strength reattachment of nanoscale polymer fibers during slip-stick experiments.

Uniformly aligned liquid crystal molecules on reformed poly(ethylene-co-vinyl acetate) layers driven by ion beam exposure

ABSTRACT The characteristics of a poly(ethylene-co-vinyl acetate) (PEVA) film formed by spin coating process and ion beam (IB) irradiation was investigated with irradiation times. A physicochemical analysis was used to analyse the suitability of the PEVA film as a uniform liquid crystal (LC) alignment layer. Atomic force microscopy (AFM) revealed an increased surface roughness after IB irradiation. X-ray photoelectron spectroscopy (XPS) analysis showed IB irradiation broke the polymer branches and increased the oxygen concentration and bonding on the surface. These derived the strong Van der Waals forces and dipole-dipole interactions between the PEVA surface and LCs. The IB irradiation generated surface anisotropy on the PEVA film and unidirectional LC alignment was achieved. Polarised optical microscopy (POM) and pre-tilt angle measurements were carried out to show the uniform LC alignment. The transmittance curve exhibited a high optical performance. These results show the promising capabilities of IB irradiated PEVA film as an alignment layer in LC displays.

Crystallization of charged gold particles mediated by nonadsorbing like-charged polyelectrolyte.

We report that the aqueous dispersions of negatively charged submicron-sized colloidal Au particles formed non-close-packed colloidal crystals by the addition of a like-charged linear polyelectrolyte, sodium polyacrylate (NaPAA). Au particles often form irregular aggregates in dispersions because of a strong van der Waals force acting between them. To prevent aggregation, we introduced negative electric charges on particle surfaces. By the addition of NaPAA, colloidal crystals were formed on the bottom of a sample cell because of the supply of Au particles by sedimentation and 2D diffusion even under very dilute conditions. Interparticle potential calculations demonstrated that the addition of NaPAA caused depletion attraction between the particles as well as a significant reduction in the interparticle repulsion because of the electrostatic screening effect. However, the electrostatic repulsion was strong enough to prevent the direct contact of particles in the excluded region between Au particles. Large-area crystals could be obtained by tilting the sample cell. By drying the sample, the Au particles came into contact and the non-space-filling crystals changed into closest packed crystals. These closest packed crystals exhibited a significant enhancement of Raman scattering intensity because of high hot-spot density.

First-Principles Study on Graphene/Mg2Si Interface of Selective Laser Melting Graphene/Aluminum Matrix Composites

The bonding strength of a Gr/Mg2Si interface was calculated by first principles. Graphene can form a stable, completely coherent interface with Mg2Si. When the (0001) Gr/(001) Mg2Si crystal plane is combined, the mismatch degree is 5.394%, which conforms to the two-dimensional lattice mismatch theory. At the interface between Gr/Mg2Si, chemical bonds were not formed, there was only a strong van der Waals force; the interfaces composed of three low index surfaces (001), (011) and (111) of Mg2Si and Gr (0001) have smaller interfacial adhesion work and larger interfacial energy, the interfacial energy of Gr/Mg2Si is much larger than that of α-Al/Al melt and Gr/Al interfacial (0.15 J/m2, 0.16 J/m2), and the interface distance of a stable interface is larger than the bond length of a chemical bond. The interface charge density difference diagram and density of states curve show that there is only strong van der Waals force in a Gr/Mg2Si interface. Therefore, when the Gr/AlSi10Mg composite is stressed and deformed, the Gr/Mg2Si interface in the composite is easy to separate and become the crack propagation source. The Gr/Mg2Si interface should be avoided in the preparation of Gr/AlSi10Mg composite.

Mechanical Properties of Hybrid Graphene Nanoplatelet-Nanosilica Filled Unidirectional Basalt Fibre Composites.

Basalt fibre (BF) is one of the most promising reinforcing natural materials for polymer composites that could replace the usage of glass fibre due to its comparable properties. The aim of adding nanofiller in polymer composites is to enhance the mechanical properties of the composites. In theory, the incorporation of high strength and stiffness nanofiller, namely graphene nanoplatelet (GNP), could create superior composite properties. However, the main challenges of incorporating this nanofiller are its poor dispersion state and aggregation in epoxy due to its high surface area and strong Van der Waals forces in between graphene sheets. In this study, we used one of the effective methods of functionalization to improve graphene’s dispersion and also introducing nanosilica filler to enhance platelets shear mechanism. The high dispersive silica nanospheres were introduced in the tactoids morphology of stacked graphene nanosheets in order to produce high shear forces during milling and exfoliate the GNP. The hybrid nanofiller modified epoxy polymers were impregnated into BF to evaluate the mechanical properties of the basalt fibre reinforced polymeric (BFRP) system under tensile, compression, flexural, and drop-weight impact tests. In response to the synergistic effect of zero-dimensional nanosilica and two-dimensional graphene nanoplatelets enhanced the mechanical properties of BFRP, especially in Basalt fibre + 0.2 wt% GNP/15 wt% NS (BF-H0.2) with the highest increment in modulus and strength to compare with unmodified BF. These findings also revealed that the incorporation of hybrid nanofiller contributed to the improvement in the mechanical properties of the composite. BF has huge potential as an alternative to the synthetic glass fibre for the fabrication of mechanical components and structures.

Degradations of endocrine-disrupting chemicals and pharmaceutical compounds in wastewater with carbon-based nanomaterials: a critical review

Although water occupies 75% of the earth's surface, only 0.0067% of the total water is available for human activities. These statistics further decline with the population growth and consequent multiplication in the amount of annual waste produced. The demand for clean and safe drinking water has always been a prime concern in the global scenario. Among various types of waste materials, endocrine-disrupting chemicals (EDCs) and pharmaceutical effluents have become a constant threat to the aquatic ecosystem and possess challenges worldwide. Endocrine-disrupting chemicals (EDCs) are a mixed group of emerging concern chemicals with the ability to mimic the mechanisms of biosynthesis, transport, and metabolism of hormones. These chemicals pose various health threats such as early puberty, infertility, obesity, diabetes, reproductive disorders, cancerous tumors, and related disorders (immune cells, hormones' activity, and various organs). On the other hand, pharmaceutical compounds such as antibiotics also harm the natural environment, human health, and soil microbiology. Their low concentration, ranging from a few ng/L to μg/L, gives rise to a micro-pollution phenomenon, which makes it difficult to detect, analyze, and degrade in wastewater treatment plants. Activated carbons (ACs) and other adsorbents, including naturally occurring materials (wood, keratin) are considered as nanomaterials (NMs) reference for the separation of organic pollutants. It is generally acknowledged that mass-transfer phenomena control sorption kinetics at the liquid/solid interface, with retention controlled by the sorbent/sorbate properties. Therefore, the type of interaction (strong or weak van der Waals forces) and the hydrophilic/hydrophobic properties of the adsorbent are two crucial factors. Besides, EDCs and pharmaceutical compound sorption on such kinds of nanoporous solids depend on both the molecule size and charge density. The applications of nanomaterials on non-conservative methods, like advanced oxidation processes or AOPs (e.g., photocatalysis and Fenton reaction), are contemplated as more apt in comparison to conservative technology like reverse osmosis nanofiltration, and adsorption, etc. One of the reasons is that AOPs generate free radicals (hydroxyls), which are strong oxidants for the demineralization of organic compounds and the extreme case that hydroxyl radicals can attack any kinds of pollutants with the generation of only water and carbon dioxide as final products. AOPs may imply the use of NMs as either catalysts or photocatalysts, which improve the selective removal of the target pollutant. Therefore, various literature reviews have revealed that there is a timely need to upgrade the efficiency of the remediation approaches to protect the environment against EDCs and pharmaceuticals adequately. There is currently a lack of definitive risk assessment tools due to their complicated detection and associated insufficiency in the health risk database. Hence, our present review focuses on applying carbon-based nanomaterials to remove EDCs and pharmaceuticals from aqueous systems. The paper covers the effect of these pollutants and photocatalytic methods for treating these compounds in wastewater, along with their limitations and challenges, plausible solutions, and prospects of such techniques.

One-Pot Hydrothermal Synthesis of Solution-Processable MoS2/PEDOT:PSS Composites for High-Performance Supercapacitors.

It is challenging to hydrothermally synthesize solution-processable MoS2, as the strong van der Waals force between MoS2 nanosheets induces self-assembly of agglomerates. Here, we introduce poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) into the precursor to impede aggregate formation in the hydrothermal process. A hybrid MoS2/PEDOT:PSS (MP) hydrogel is formed due to the electrostatic interactions between the negatively charged MoS2 and positively charged PEDOT chains. This hydrogel can be easily dispersed in water for subsequent solution processing such as vacuum filtration to form free-standing flexible films or extrusion 3D printing to create novel patterns. The MP film with a fracture strength of 18.59 MPa displays excellent electrochemical performance in both aqueous Na2SO4 electrolyte (474 mF cm-2) and solid-state PVA-H3PO4 electrolyte (360 mF cm-2). Flexibility and robustness can be evidenced by high capacitance retention rates of 94 and 89% after being repeatedly bent to 180° for 5000 cycles in aqueous and solid-state electrolytes, respectively.

Investigation of interactions between oxygen-containing groups and water molecules on coal surfaces using density functional theory

The oxygen-containing group is a crucial factor that affects the water wettability of a coal surface. An investigation of the interaction between the oxygen-containing group and water molecule is conducive for understanding the water wettability of the coal surface. In this study, water contact angle measurements and X-ray photoelectron spectroscopy were used to explore the surface wettability and oxygen-containing groups for different rank coals respectively. The adsorption behavior of water molecules on the coal surface was investigated using the density functional theory. The results indicated that the oxygen-containing group enhances the hydrophilicity of the coal surface. In oxygen-containing groups, oxygen atoms possess strong nucleophilicity, and enhance the electrophilicity of hydrogen atoms attached to them. The oxygen atom in the water molecule prefers to form strong hydrogen bonds with the hydrogen atom that is attached to the oxygen atom in the oxygen-containing group. The hydrogen atom in the water molecule prefers to face down, thereby generating a strong van der Waals force on the carbon rings. Based on the combined action of hydrogen bonds and van der Waals force, the effect of oxygen-containing groups on water adsorption capability follows the order –OOH > –OH > –CHO > –OCH3.

Hard Carbon Nanotube Sponges for Highly Efficient Cooling via Moisture Absorption-Desorption Process.

Heat dissipation is a serious limitation for increasingly miniaturized and functionalized electronics, resulting in the continuous need for developing highly efficient cooling methods. Here, utilizing the strong van der Waals force between super-aligned carbon nanotubes (SACNTs), a self-supported three-dimensional (3D) CNT/CaCl2 radiator with a more outstanding cooling performance than Al cooling fins was designed. Unlike the soft CNT sponges, these 3D structures could sustain a high pressure of 4.5 MPa with a small compression of 10% and thus are defined as hard CNT sponges. Hard CNT sponges show a 44.3% higher cooling efficiency than commercial Al cooling fins at a humidity of 50% due to the massive latent heat of water combining with the high thermal conductivity of CNTs and the high emissivity of the composites. The self-adjusting moisture absorption-desorption process could dissipate heat by water evaporation when electronics work at high power and spontaneously absorb moisture to regenerate the sponges at the standby mode of electronics. Besides, hard CNT sponges possess a much lower density (0.98-1.70 g cm-3) than aluminum (2.7 g cm-3). This high-performance cooler provides an alternative thermal management method for electronics.

Study on effects of co-solvents on the structure of DhaA by molecular dynamics simulation

With the increasing application of enzymes in various research fields, the choices of co-solvents in enzymatic preparations which directly related to the catalytic activity have been attracted attention. Thus, researching on the stabilization or destabilization behaviors of enzymes in different solvents is extremely essential. In this study, the structural changes of DhaA in two typical aprotic co-solvents (acetonitrile and tetrahydrofuran) were firstly investigated by molecular dynamics (MD) simulation. The simulation results revealed the strong van der Waals force between co-solvents and DhaA which could induce the structural change of enzyme. Interestingly, the differences of molecular size and the electrostatic force with enzyme of two co-solvents led to quite different influences on DhaA. As for acetonitrile, solvent molecules could penetrate into the catalytic site of DhaA which promoted by the electrostatic interaction. On the contrary, tetrahydrofuran molecules were mainly distributed around the catalytic site due to the relative weak electrostatic interaction and steric resistance effect. It can be concluded that different co-solvent can affect the key domains, substrate pathway and catalytic pocket of DhaA. Communicated by Ramaswamy H. Sarma

Study on Interaction of Coomassie Brilliant Blue G-250 with Bovine Serum Albumin by Multispectroscopic

Aim of present study was to investigate the interaction of coomassie brilliant blue G-250 (CBBG-250) with bovine serum albumin (BSA) by the multispectroscopic methods. Fluorescence-data showed that the complex of BSA-CBBG-250 forming made the intrinsic fluorescence quenching of BSA by CBBG-250 interaction. BSA also could interact with CBBG-250 and the CBBG-BSA complexes formed in a molar ratio of 1:1. UV–Vis results displayed that the apparent binding (association) constant Ka of CBBG-250 with BSA was 5.03 × 104 (298 K), 3.04 × 104 (303 K), 2.84 × 104 (308 K) and 1.99 × 104 (313 K) L mol−1 at different temperatures, respectively. The enthalpy change (△H) and entropy change (△S) were respectively calculated to be − 45.32 kJ mol−1 and − 139.18 J mol−1 K−1, indicating that the hydrogen bonds and Van der Waals forces played dominant roles in the interaction. The results showed that the diphenylamine structure and amino acid residues in the Coomassie Brilliant Blue G-250 had a strong Van der Waals force. The phenyl sulphonic acid group undergoes electrostatic interactions and hydrogen bond interactions with basic amino acids; the compound Coomassie Brilliant Blue G-250 can form a stable complex with BSA.

The cocrystal mechanism of HMX and LLM-105 by theoretical simulations

Isothermal-isobaric molecular dynamics (NPT-MD) simulations and density functional theory (DFT) calculations were performed to explore the cocrystal formation mechanism of energetic materials. Based on the morphologically dominant crystal habits of HMX (octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine) and LLM-105 (2,6-diamino-3,5-dinitropyrazine-l-oxide), six interface structures of HMX with LLM-105 have been established to obtain the interaction energy, radial distribution function (RDF), electrostatic potential and mechanical properties. It revealed that the interaction energies in different models are different, owing to the various molecular orientation and stackingmanner of the contacted crystal face of HMX and LLM-105. The (1 1 –1)/(1 1 0) interface is mainly governed by the O···H hydrogen bond and strong van der Waals forces and this model possesses the largest interaction energy. Electrostatic potentials indicate (1 1 –1)/(1 1 0) interface blending the strongest, which reveals that the cocrystal process is stronglyrelevant to the interface behavior of (1 1 –1)/(1 1 0) among the 6 interfaces. Moreover, the mechanical parameters show that the (1 1 –1)/(1 1 0) interface structure (VI) exhibits excellent ductility and fracture strength. Additionally, this work presents a novel insight, which from the crystal face of HMX and LLM-105 as well as the interaction behavior to research the cocrystal mechanism.

Rosin-based chiral wormlike Micelles: Rheological behavior and its application in preparing ultrasmall gold nanoparticles

Innovations in surfactant structures are a feasible way to prepare unique molecular aggregates with interesting properties. Herein, taking dehydroabietic acid as the starting material, a new amine oxide surfactant, abbreviated as R-8-AO, was synthesized. Cryogenic transmission electron microscopy (cryo-TEM) images and circular dichroism (CD) spectra reveal that at suitable concentrations, R-8-AO molecules form rarely discovered right-handed chiral wormlike micelles, which have a cross-sectional diameter of 5–6 nm. The overlap concentration of R-8-AO is approximately 8 mM, above which the wormlike micelles began to entangle in solutions. Due to the strong van der Waals forces between R-8-AO molecules, the scaling law gives an exponent of 7.88, which is higher than the theory predicted value. Gold nanoparticles were synthesized in-situ by irradiating mixed solutions of HAuCl4 and wormlike micelles formed by R-8-AO with UV light. These ultrasmall spherical gold nanoparticles, which are located at the surface of wormlike micelles, have a uniform particle size of 3 ± 1 nm, as observed by TEM. In addition, the gold nanoparticles form a worm-like morphology induced by the wormlike micelles, showing soft-aggregate-directed nanoparticle assembly. This work is first to reveal the effectiveness of preparing ultrasmall gold nanoparticles with new morphological wormlike micelles as soft templates. The resulting organic-inorganic hybrid aggregates are also expected to find applications in catalysis and electronic fields.

Chemical activation of hollow carbon nanospheres induced self-assembly of metallic 1T phase MoS2 ultrathin nanosheets for electrochemical lithium storage

Ultrathin nanosheets made by transition metal dichalcogenide show the potential as high-capacity anode materials for lithium ion batteries (LIBs). However, the tendency of restacking individual nanosheet due to strong van der Waals force, a dramatic volume variation upon continuous cycling, as well as poor intrinsic conductivity greatly restrict their practical applications. In this work, high content metallic phase molybdenum disulfide (1T/2H–MoS2) ultrathin nanosheets with higher intrinsic conductivity and extended interlayer distance are vertically assembled on the outer surface of chemically activated hollow carbon nanospheres (CAHCSs) through a facile solvothermal method. Phase structure, chemical composition, and microstructure studies show that the obtained composites (CAHCSs@1T/2H–MoS2) have optimized structural and compositional advantages to efficiently store lithium ions. When evaluated as anodes for LIBs, the CAHCSs@1T/2H–MoS2 electrode show excellent fast and stable lithium storage properties. In specific, the CAHCSs@1T/2H–MoS2 electrode delivers a large reversible capacity of 831 mAh g−1 at 1 A g−1 after 200 cycles. At a higher current density of 2 A g−1, the CAHCSs@1T/2H–MoS2 electrode has a reversible capacity of 863 mAh g−1. The proposed electrode design strategy provides an alternative route to promote the ion storage in transition-metal-dichalcogenides-based materials.

MOF-derived hybrid nanoarchitectured carbons for gas discrimination of volatile aromatic hydrocarbons

Two-dimensional layered graphene nanosheets are very interesting with regard to molecular sensing and vapor discrimination between aromatic hydrocarbons and their aliphatic analogues. However, graphene oxide (GO) suffers from stacking due to strong van der Waals forces between the adjacent nanosheets, thus reducing the surface area of exposure and limiting molecular ion transport in porous electrodes. Mixing GO with nanoporous carbon polyhedra derived from zeolitic imidazolate framework-8 (ZIF-8) generates a 3D continuous framework of hybrid nanoarchitectured hollow carbon macropores coated with reduced GO (rGO). This 3D hollow graphitic carbon framework (HGCF) synergistically combines π-rich-electron nanospaces with a high surface area and a large hierarchical pore volume, both of which are particularly beneficial as porous electrodes for selective detection of hazardous aromatic hydrocarbon vapors over their aliphatic analogues because of reinforced noncovalent π–π interactions with a π-conjugation system of aromatic rings. A designed quartz crystal microbalance (QCM) nanosensor coated with an HGCF heterostructure clearly shows the high impact of π-rich-electrons in graphene as sensing antennae on the molecular discrimination of vaporized toxic aromatic hydrocarbons as compared to carbon polyhedron shapes derived from the ZIF-8 of low sp2-graphitized carbon content.

Figure of Merit Enhancement of Surface Plasmon Resonance Biosensor Using Ga-Doped Zinc Oxide in Near Infrared Range

This work presents a surface plasmon resonance biosensor for the figure of merit enhancement by using Ga-doped zinc oxide (GZO), i.e., nanostructured transparent conducting oxide as plasmonic material in place of metal at the telecommunication wavelength. Two-dimentional graphene is used here as a biorecognition element (BRE) layer for stable and robust adsorption of biomolecules. This is possible due to stronger van der Waals forces between graphene's hexagonal cells and carbon-like ring arrangement present in biomolecules. The proposed sensor shows improved biosensing due to fascinating electronic, optical, physical, and chemical properties of graphene. This work analyses the sensitivity, detection accuracy, and figure of merit for the GZO/graphene SPR sensor on using the dielectric layer in between the prism and GZO. The highest figure of merit of 366.7 RIU−1 is achieved for the proposed SPR biosensor on using the nanostructured GZO at the 3000 nm dielectric thickness. The proposed SPR biosensor can be used practically for sensing of larger size biomolecules with due availability of advanced techniques for the fabrication of the nanostructured GZO and graphene.

Flexural Properties of Halloysite Nanotubes (HNTS) and Carbon Nanotubes (CNTS) Toughened Epoxy Composites

In this research, four different concentrations of halloysite nanotubes and carbon nanotubes (0wt%, 0.2 wt%, 0.5 wt% and 1 wt%) were produced using solution casting method. Both fillers were dispersed using bath sonicator for 10 minutes. Flexural properties, surface roughness and microhardness were studied. The highest flexural modulus and flexural strength were observed in the 0.2 wt% HNTs-epoxy composites, where the maximum values were 36.6% and 82% respectively. The maximum surface roughness was recorded in the case of 0.2 wt% HNTs-epoxy composites. The highest microhardness value was found in the 0.5 wt% HNTs-epoxy composites where the microhardness improved by 80%. The results suggest, HNTs were easily dispersed in epoxy matrix than CNTs, at shorter processing time. From the SEM images, it can be observed that, HNTs significantly changed the microstructure of the nanocomposites, as there were many straight and elevated crack lines, this can be associated with the toughening mechanism offered by the filler. CNTs on the other hand, had influenced on the micro cracks and showed semi-parabolic pattern. However, the flexural properties of CNTs are slightly lower than HNTs because CNTs have strong van der Waals force and as a result very difficult to disperse by simple sonication. HNTs can be utilised as an alternative to CNTs, since the dispersion state is better even though at minimum sonication time.

Compartmentalization of gold nanoparticle clusters in hollow silica spheres and their assembly induced by an external electric field

Assembly of plasmonic nanoparticle clusters having hotspots in a specific space is an effective way to efficiently utilize their plasmonic properties. In the assembly, however, bulk-like aggregates of the nanoparticles are readily formed by strong van der Waals forces, inducing a decrease of the properties. The present work proposes an advanced method to avoid aggregation of the clusters by encapsulating into a confined space of hollow silica interior. Hollow spheres incorporating gold nanoparticle clusters were synthesized by a surface-protected etching process. The observation of inner nanoparticles with liquid cell transmission electron microscopy experimentally proved that the nanoparticles moved as a cluster instead of as dispersed nanoparticles within the water-filled hollow compartment. The hollow spheres incorporating the nanoparticle clusters were assembled in the vicinity of electrodes by application of an external AC electric field, resulting in the enhancement of Raman intensities of probe molecules. The nanoparticle-cluster-containing hollow spheres were redispersed when the electric field was turned off, showing that the hollow silica spheres can act as a physical barrier to avoid the cluster aggregation. The Raman intensities were reversibly changed by switching the electric field on and off to control the assembled or dispersed states of the hollow spheres.

Multiscale design, interaction mechanism and performance of CL-20/Al energetic composites with embedded structure.

In order to design and prepare hexanitrohexaazaisowurtzitane/aluminum (CL-20/Al) composites, the contact state of CL-20 with aluminum particles under different mixed solvent contents were calculated with the method of dissipative particle dynamics (DPD). Then the modified attachment energy (AE) model was applied to predict the morphologies of CL-20 in ethyl acetate, hexane and ethyl acetate/hexane mixed solvents. Furthermore, the morphologies, the surface element distribution, the sensitivity and the energy performance of CL-20/Al composites prepared with the solvent/non-solvent method were characterized, and the interaction mechanism were also obtained. The results achieved show that phase separation phenomenon becomes obvious with the decrease of ethyl acetate/n-hexane mixed solvent content. CL-20/aluminum particles will form the composites of aluminum particles embedded in CL-20 crystal when the solvent content is zero. The order of modified attachment energies for ethyl acetate/hexane mixed solvents on CL-20 faces is (011) > (110) > (101) ≈ (11−1) ≈ (10−1) > (002). Besides that, the crystalline morphology of CL-20 in acetate/hexane mixed solvents is spindle-shaped. There are many Al particles embedded in CL-20 crystals of CL-20/Al composites prepared by using solvent/non-solvent method. The calculated results agree well with the experimental results. In CL-20/Al composites, aluminum particles interact with CL-20 mainly through hydrogen bond and strong van der Waals force. The sensitivity of CL-20/Al composites decreased obviously compared with pure CL-20 and mechanical mixing composites. Besides, the CL-20/Al composites with embedded structure can increase the explosion reaction temperature to 791.2 K, which has obvious energy advantage compared with CL-20/Al physical mixture.