Three-dimensional Sandwich Structures Research Articles

A multifunctional flexible composite phase-change film with excellent solar driven thermal management

The development of multifunctional films with integrated temperature regulation, photothermal conversion, and bendability is urgently needed for personal thermal management products. In this paper, aminated multi-walled carbon nanotubes modified phase-change microcapsules (ACNTs-PCMC) were synthesized. Subsequently, a flexible polyvinyl alcohol (PVA)/graphene/ACNTs-PCMC composite film (PGAMF) with a three-dimensional sandwich structure was prepared by a simple tape-casting method. The obtained PGAMF films possessed a phase-change enthalpy of 45.5 ± 0.7 J/g. The designed sandwich structure can fix the ACNTs-PCMC microcapsules inside the PGAMF films through the bonding effect of the PVA to prevent them from falling off and sliding, so that the PGAMF composite films have the proper mechanical properties and excellent flexibility. More importantly, the PGAMF composite films had a high photothermal conversion efficiency of 88.8 %. In the cold environment, the center temperature of the PGAMF composite film adhered to the fiber fabric driven by a low solar radiation was 14.5 ± 0.5 °C higher than that of the fiber fabric without the PGAMF composite film. Therefore, the multifunctional composite films with flexibility, heat storage and solar-to-heat conversion prepared in this study have broad application scenarios in heat preservation in low temperature areas and solar-driven thermal management engineering.

Fabrication of a Three-Dimensional Microfluidic System from Poly(methyl methacrylate) (PMMA) Using an Intermiscibility Vacuum Bonding Technique.

In this study, the fabrication of microfluidic chips through the bonding of poly (methyl methacrylate) (PMMA) boards featuring designed patterns to create a three-dimensional sandwich structure with embedded microchannels was explored. A key focus was optimization of the interface quality of bonded PMMA pairs by adjusting the solvent, such as such as acetone, alcohol, and their mixture. Annealing was conducted below 50 °C to leverage the advantages of low-temperature bonding. Because of the differences in the chemical reactivity of PMMA toward acetone, alcohol, and their combinations, the resulting defect densities at the bonding interfaces differed significantly under low-temperature annealing conditions. To achieve the optimal sealing integrity, bonding pressures of 30 N, 40 N, and 50 N were evaluated. The interface was analyzed through microstructural examination via optical microscopy and stress measurements were determined using digital photoelasticity, while the bonding strength was assessed through tensile testing.

Fabrication and compression properties of continuous carbon fiber reinforced polyether ether ketone thermoplastic composite sandwich structures with lattice cores

Lightweight and high-strength sandwich structures with advanced materials are essential for the sustainable development of future industrial development. This paper focuses on investigating the fabrication technology and compression properties of the three-dimensional sandwich structure with lattice cores fabricated by using the continuous carbon fiber reinforced thermoplastic polyether ether ketone (CCF/PEEK). A novel fabrication technology for continuous carbon fiber reinforced thermoplastic polyether ether ketone lattice core is proposed utilizing the unique characteristic of repeated thermoforming of continuous carbon fiber reinforced thermoplastic polyether ether ketone. A mould was designed and then the continuous carbon fiber reinforced thermoplastic polyether ether ketone lattice cores were fabricated. Typical adhesive technology is selected to connect facesheets and lattice cores. The out-of-plane compression behaviors of continuous carbon fiber reinforced thermoplastic polyether ether ketone sandwich structures with lattice cores were investigated by experiment and simulation. Compared with the experimental results, the reliability and correctness of the simulation model were verified. By dint of the simulation model, the effect of stacking sequence of the lattice cores on the structural compression properties was investigated, and the correctness of lattice cores adopted [Formula: see text] stacking sequence in this paper was proved. The continuous carbon fiber reinforced thermoplastic polyether ether ketone lattice sandwich structures exhibit the competitive compression strength with other thermoplastic sandwich structures and surpasses some metal foams at a range of densities.

Novel method for preparation of metal-sulfide@reduced-graphene-oxide with high energy storage performance

Transition-metal sulfide with high theoretical capacity is a promising anode material. However, the poor conductivity and pulverization of the transition-metal sulfide caused by huge volume changes lead to a fast decay in specific capacity. In this study, we prepared a three-dimensional sandwich-structured anode material consisting of metal sulfides and reduced graphene oxide (rGO), which can address the above problems. The anode material is composed of Ni7S6/MnS2 micro/nanosheets uniformly attached on the rGO synthesized by an in-situ sulfuration of a NiMn2O3(OH)4@rGO precursor. The Ni7S6/MnS2@rGO composite exhibited a high electrochemical performance, which is mainly ascribed to the three-dimensional sandwich-structures, because it can well relieve the volume change and promote electron mobility and ion diffusion in the discharge/charge process. Furthermore, this method can be used to prepare other sulfides such as NiS2@rGO and Ni7S6/CoS2@rGO. The proposed universal preparation method and excellent electrochemical performance of Ni7S6/MnS2@rGO make the composite attractive anode material.

Hierarchical sandwiched Fe3O4@C/Graphene composite as anode material for lithium-ion batteries

A three-dimensional hierarchical sandwich structured Fe3O4@C/Graphene nanocomposite was synthesized with a facile hydrothermal method, followed by carbonization process. The Fe3O4@C/Graphene nanocomposite consists of well-dispersed carbon enwrapped Fe3O4 nanoparticles anchored on graphene layers. The three-dimensional sandwich structure and the wrapping carbon effectively improve the mechanical stability and conductivity of encapsulated Fe3O4. The as-prepared Fe3O4@C/Graphene composite delivers a specific capacity of 1253.3mAhg−1 at the first cycle and 901.5mAhg−1 after 200cycles at 200mAg−1. Even at 1500mAg−1, the Fe3O4@C/Graphene nanocomposite is able to deliver a discharge capacity of 592.3mAhg−1. The good cycle and rate performance of Fe3O4@C/Graphene anode can be attributed to its micro−/mesoporous structure with large specific surface area, which not only provides more transmission paths and active sites, but also reduces the diffusion impedance in electrolyte to realize fast transport of Li ions.

A novel flexible electrode with coaxial sandwich structure based polyaniline-coated MoS2 nanoflakes on activated carbon cloth

The combination of polyaniline (PANI)-coated molybdenum disulfide (MoS2) and activated carbon cloth (CC) is proposed on the basis of a facial hydrothermal and in situ polymerization. The flexible composite of CC/MoS2/PANI with a three-dimensional sandwich structure displays remarkable electrochemical performance, in terms of the highest specific capacitance of 972 F g−1 with a current density of 1 A g−1, compared to CC/MoS2 (425 F g−1) and CC/PANI (440 F g−1), good rate performance, low internal resistance, and more importantly, a long cycling life and notable electrochemical stability with retention of the initial specific capacitance at 87% after 5000 cycles (a large current density of 10 A g−1). The flexible self-assembled supercapacitors (FSCs) can display good electrochemical performance with the specific capacitance of 193.3 F g−1, as well as outstanding mechanical flexibility. Furthermore, the performance of this flexible device was obviously decreased under various bending states. The present composite design concept opens a new path for the discovery of efficient electrode materials with three-dimensional sandwich structures.

A free vibration analysis of three-dimensional sandwich beams using hierarchical one-dimensional finite elements

This paper presents a family of beam higher-orders finite elements based on a hierarchical one-dimensional unified formulation for a free vibration analysis of three-dimensional sandwich structures. The element stiffness and mass matrices are derived in a nucleal form that corresponds to a generic term in the displacement field approximation over the cross-section. This fundamental nucleus does not depend upon the approximation order nor the number of nodes per element that are free parameters of the formulation. Higher-order beam theories are, then, obtained straightforwardly. Timoshenko's classical beam theory is obtained as a special case. Short and slender beams are investigated. Simply supported, cantilevered and clamped-clamped boundary conditions are considered. Several natural frequencies as well as the corresponding modes are investigated. Results are validated in terms of accuracy and computational costs towards three-dimensional finite element solutions. The proposed hierarchical models, upon an appropriate choice of approximation order, yield accurate results with a reduced computational cost.

A novel acetylene black/sulfur@graphene composite cathode with unique three-dimensional sandwich structure for lithium-sulfur batteries

A novel acetylene black/sulfur@graphene composite (AB/S@G) with unique three-dimensional sandwich structure was successfully prepared via an in situ sulfur deposition strategy and self-assembly. Acetylene black as conductive carbon skeleton and graphene nanosheets as physical shields played an extremely important role for improving the electrochemical performances of the AB/S@G cathode. Compared with the AB/S cathode, the AB/S@G cathode with a sulfur content of 54wt% exhibited a high utilization of sulfur, an enhanced cyclical stability, and an excellent rate capability. The AB/S@G cathode came true a high sulfur utilization of 95.73% after undergoing a high initial discharge capacity of 1603.5mAhg−1 at a current density of 200mAg−1, much higher than that (71.78%) of the AB/S cathode. The excellent electrochemical performances were principally attributed to the combined effect of graphene nanosheets and acetylene black, which provided an improved electrical conductivity for the sulfur cathode, effective restraining for soluble polysulfides, and powerful buffer for the volume changes of sulfur during cycling.

Three-dimensional magneto-resistive random access memory devices based on resonant spin-polarized alternating currents

Selective switching of a magneto-resistive random access memory (MRAM) multilayer stack is demonstrated using resonant spin-polarized alternating currents (AC) superimposed on spin-polarized direct currents. Finite element micromagnetic simulations show that the use of frequency triggered AC allows one to maximize the transferred spin transfer torque selectively in order to merely reverse the magnetization of a single storage layer in a stack. Using layers with different resonance frequencies, which are realized by altering the anisotropy constants, allows one to address them by tuning the AC frequency. A rapid increase of the storage density of MRAM devices is shown by using three-dimensional sandwich structures.

Effects of Microstructure of Mesophase Pitch Precursor on the Compression Behaviour of Carbon Foam

The compression behaviour of carbon foams derived from synthetic naphthalene based and coal tar based mesophase pitch is studied. After carbonization and graphitization, the structure of carbon foam is modified obviously and compression behaviour decreased dramatically due to the transition of foam from two-dimensional turbostratic structures to graphite structures. The SEM, X-Ray diffraction and compression behaviour are used in the study of modification of mechanical properties. The results show that the compressive strength of carbon foam obtained from synthetic mesophase pitch is only 30% of the foam obtained from coal tar based mesophase pitch. The SEM shows that the length of micro-cracking of foam derived from synthetic mesophase pitch is as high as 5 μm and that of foam derived from coal tar based mesophase pitch is less than 2 μm. The causes of the differences in properties focused on rod structure of naphthalene based pitch transformed easier to three-dimensional sandwich structure.