Fabrication Of Such Composites Research Articles

Thermally tunable ethanol impregnated PDMS/CoZTO/SWCNT composite architecture for smart electromagnetic shielding

Shape memory elastomer composites with externally stimulated shielding capability are greatly sought to protect high-end artificial intelligence-based electrical and telecommunication devices in the military, aerospace, robotics, etc., from electromagnetic interference (EMI). However, the fabrication of such composites integrated with externally responsive green EMI shielding capabilities is promising but greatly challenging. Herein, ethanol (thermally active phase) mixed polydimethylsiloxane (PDMS)/single wall carbon nanotube (SWCNT)/cobalt doped zinc tin oxide (CoZTO) hybrid composite with an active guest method was devised. This design strategy explores how the thermally controlled liquid-gas phase transition led microstructural modifications regulate the macroscopic shielding features like absorption enhancement and reflection minimization. The composite adapts the 72.18 % volumetric actuation by liquid-to-vapor phase transition of ethanol at 80 °C, promoting the total EMI shielding value up to 48.77 dB from 18.4 dB at 20 GHz due to microstructure induced electromagnetic modifications. Additionally, a green index of 7.2 confirms the absorption dominance over reflection shielding in the studied composite. Furthermore, ethanol-generated foamed architecture of composite offers pressure-sensitive on-off shielding tunability, which accounts for the potential use in manufacturing advanced RF switches.

Glass-based composites comprised of CaWO4:Yb3+, Tm3+ crystals and SrAl2O4:Eu2+, Dy3+ phosphors for green afterglow after NIR charging

In this paper, we demonstrated the fabrication of new phosphate-based composites with green persistent luminescence after being charged with near-infrared light using the direct doping method. The composites are composed of a phosphate glass and phosphors. The 75NaPO3 − 25CaF2 and 90NaPO3 − 10NaF (in mol%) were the 2 glasses of investigation. The intense blue up-conversion emission between 450 and 500 nm upon 980 nm pumping is obtained by adding CaWO4: Tm3+, Yb3+ crystals in the glass melt before quenching whereas the green persistent luminescence is from the SrAl2O4:Eu2+,Dy3+ phosphors also added in the glass melt. The green persistent luminescence above 0.3 mcd/m2 is observed for ∼30 min after charging with 980 nm due to energy transfer between the upconverter crystals and the persistent luminescent phosphors. Here, the challenges related to the fabrication of such composites are discussed. While it is important for the blue UC emission to be intense to charge the SrAl2O4:Eu2+,Dy3+ crystals, we demonstrate that the glass matrix should not crystallize upon the addition of the different crystals. Additionally, the composites should remain translucent with limited light scattering for the blue UC emission to charge the persistent luminescent phosphors.

Low energy repair of co-continuous metal-ceramic composites using electrodeposition

The concept of self-healing materials, mainly inspired from biological systems, in the last several decades has been pursued toward fully autonomous materials and structures. Self-healing of polymers (extensively) and metals (to much less extent) have been demonstrated, however, there are no such reports for metal-ceramic composites. Metal-ceramic composites are technologically significant as structural and functional materials and are among the most expensive materials to manufacture and repair. Hence, technologies for self-healing metal-ceramic composites are of paramount importance. Here, we demonstrate a concept to fabricate and heal co-continuous metal-ceramic composites at room temperature. The composites are fabricated by infiltration of metal (here copper) into a porous alumina preform (fabricated by freeze-casting) through electroplating; a low-temperature and low-cost (by ∼60-times lower cost compared to traditional molten metal infiltration) process for fabrication of such composites. Additionally, the same electroplating process is demonstrated for healing damages such as grooves and cracks in the original composite, such that the healed composite recovers its strength by more than 80%. Such technology may be expanded toward fully autonomous self-healing structures.

Construction and hydrophilic modification of dual-network structured nonwoven/UHMWPE composite membranes for water processing.

Water pollution caused by the continuous development of industrialization has always been a common concern of mankind. Herein, a novel strategy to fabricate a high-performance composite membrane based on dual-network structured nonwoven net/UHMWPE nanopores via a thermal phase separation and composite technique is reported. By thermal phase separation of ultra-high-molecular weight polyethylene (UHMWPE)/liquid paraffin (LP), this approach enables 3D nanopores to tightly bond with a nonwoven net to form a dual-network structure. The dual-network composite membrane possesses the integrated features of pore structure and high porosity (89.9%). After modification with hyperbranched polymers (HBPs), the composite membrane with the desirable surface chemistry achieves high-efficiency filtration (water flux = 1054 L m-2 h-1, rejection rate = 50 nm PS nanospheres almost close to 100%, and antibacterial properties). The fabrication of such composites may provide new insights into the design and development of high-performance filtration and separation materials for various applications.

CaWO4:Yb3+,Tm3+ Crystals and SrAl2O4:Eu2+,Dy3+ Phosphors in Glass-Based Composites for Green Afterglow after NIR Excitation

Here, we present the preparation of composites with green persistent luminescence using melting process. The composites are phosphate glass (75NaPO3-25CaF2 and 90NaPO3-10NaF (in mol%)) with embedded phosphors: CaWO4: Yb3+, Tm3+ crystals with blue upconversion and SrAl2O4:Eu2+,Dy3+ with green persistent luminescence. Green persistent luminescence above 0.3 mcd/m2 can be seen for ~ 30 minutes after charging with 980 nm due to energy transfer between the blue upconverter crystals and the persistent luminescent phosphors. Challenges related to the fabrication of such composites are discussed.

Molecular engineering of the surface of boron nitride nanotubes for manufacture of thermally conductive dielectric polymer composites

Recent developments in microelectronic devices have led to rising demand for polymeric nanocomposites that can simultaneously deliver enhanced thermal conduction and electrical insulation. Boron nitride nanotube (BNNT) is one of the most promising fillers for the fabrication of such composites. While being electrically insulating, effective crystal lattice vibrations allow BNNTs to achieve thermal conductivity values that can even surpass that of diamond. However, when BNNTs are surface functionalized and incorporated within polymers, their lattice vibrations are significantly suppressed, resulting in polymeric nanocomposites with thermal conductivity values only a fraction of what BNNTs can achieve in air. The aim of this study is to shed light on the underlying cause of this challenge for thermally conductive, dielectric polycarbonate (PC)/BNNT nanocomposites that were produced using two distinct surface functionalization approaches. By incorporation of BNNTs in PC, the thermal conductivity values were significantly increased. However, depending on nanotubes’ concentration, the thermal conductivity of pristine BNNTs in PC were comparable or superior to those of the functionalized nanotubes. Theoretical analysis and experimental characterization have been conducted to elucidate the fundamental impacts of surface functionalization on the lattice vibrations of BNNTs and their subsequent effects on the thermal properties of dielectric BNNT composites.

Molecular dynamics investigation of atomic mixing and mechanical properties of Al / Ti interface

With the urgent lightweight demand in the aerospace engineering and transportation industries, Al / Ti composite structures have attracted much interest due to their excellent performances compared with conventional materials. Computational simulations have contributed to the understanding of both fundamental and practical aspects of fabrication of such composites and studying of their properties. The present work reports the results of studies based on molecular dynamics simulations on the mechanical properties of an Al / Ti composite obtained by compression combined with shear strain. Tensile properties of a nanosized Ti / Al composite consisting of two single crystals obtained after different compression rates are analyzed. The loading scheme applied in the present work is a simplification of the scenario experimentally realized previously to obtain Al-matrix composites. It is confirmed that uniaxial compression combined with shear deformation is an effective way to obtain the composite structure since severe plastic deformation facilitates the diffusion process. The results indicated that a symmetrical atomic movement took place in the Ti / Al interface during deformation. However, Al atoms diffuse into the Ti block easier than Ti atoms into the Al block. Tensile tests showed that fracture took place in the Al part of the final composite sample, which means that the interlayer region where the mixing of Ti and Al atoms is observed is stronger than the pure Al part.

Microstructure and wear characterization of carbon nanotubes (CNTs) reinforced aluminum matrix nanocomposites manufactured using selective laser melting

Aluminum matrix composites are attractive in aerospace and automobile industry due to its low density, high strength and high corrosion resistance. Additive manufacturing methods such as selective laser melting enable the fabrication of such composites with a complex geometry, and the processing of novel, customized, tailored hybrid materials with unique hierarchical microstructures across multiple length scales. However, the microstructure evolution, wear resistance, frictional behavior under different fabrication and operation conditions of such composites still need to be explored. This study aims to fill the research gap in microstructure evolution and wear characterization of SLM-produced CNTs reinforced aluminum matrix nanocomposites. The surface characteristics, density, wear groove morphology, and surface damages in wear tests were examined. It was determined with SEM/EDS that the major phases of SLM-processed CNTs/Al-based nanocomposites were Al9Si and Si. These phases formed during the SLM process within the composites changed their wear behavior drastically. The wear surfaces were undergoing severe plastic deformation and progressive pitting. The wear rate of CNTs/AlSi10Mg nanocomposites specimens is about 33% lower than that of AlSi10Mg specimens. The higher wear resistance of the CNTs/AlSi10Mg nanocomposites specimens with shallow and narrow wear groove is attributed to the CNTs reinforcement induced higher surface hardness and also the unique hierarchical microstructure of the nanocomposites. The results showed that the SLM-produced CNTs reinforced aluminum matrix nanocomposites have good potentials to be an alternative to pure AlSi10Mg counterparts in terms of hardness, strength, frictional and wear behavior.

A comparative study of energy harvesting performance of polymer‐piezoceramic composites fabricated with different piezoceramic constituents

Polymer-piezoceramic composites harness the flexibility of polymer and piezoelectric properties of ceramics to offer flexible piezoelectric materials for use in energy harvesting applications. Although, there is a general temptation to use piezoceramics which exhibits high piezoelectric coefficient (d33) in the fabrication of such composites, there are limitations posed by the processing conditions of the composite which eventually determines their overall performance. In the present work we have explored this aspect in detail. We fabricated composites with polyvinylidene fluoride (PVDF) as the polymer and three different piezoceramic powders namely BaTiO3 (BT), Ba(Ti0.97Sn0.03)O3 (BTS) and Sm-doped Pb (Mg1/3Nb2/3)O3-PbTiO3(Sm-PMN-PT). Our focus here is to understand the role of grain size of the ceramic powders in determining the dielectric, piezoelectric, and energy harvesting performance of the composites. To broaden the perspective, the results are compared with another analogous composite 0.59PbTiO3-0.41Bi(Zr0.5Ni0.5)O3 (PT-BNZ)-PVDF reported before. We found that, although, the dense ceramic specimen of Sm-PMN-PT exhibits exceptionally large d33, the composite with PT-BNZ exhibited the best piezoelectric and energy harvesting performance. BT, BTS and Sm-PMN-PT composites showed maximum surface power density of 6.24, 12.81 and 23.18 μW/cm2, respectively, and volume power density of 416.18, 854.1 and 1104 μW/cm3, respectively. Whereas surface power density and volume power density of PT-BNZ was 101.80 μW/cm2 and 5088.80 μW/cm3 respectively. We have also attempted to establish a correspondence between the piezoelectric response, energy harvesting performance and the poling induced domain reorientation/structural changes in the ceramic grains of the composites.

3D-printed polymer composites with acoustically assembled multidimensional filler networks for accelerated heat dissipation

Polymer composites containing thermally conductive fillers show great promise in solving the overheating issue which is critical for electronic devices. Recent successes in developing functional polymer composites rely on the excellent filler property and heavy loading. Yet the intensive filler loading leads to challenges in manufacturing and composite properties. This study reports an alternative method for functional particle-polymer composite design and fabrication: instead of heavy loading, a small amount of filler composes highly concentrated multidimensional network functioning as active paths for heat dissipation in the polymer matrix. A novel 3D printing technique named acoustic field-assisted projection stereolithography realizes the fabrication of such composites. The local filler weight ratio in the network is > 7 times of the feedstock filler loading. With the same feedstock, the patterned composite exhibits >10 times higher efficiency in heat dissipation, compared to the uniform composite. With the same amount of fillers embedded, the patterned composite accelerates the heat dissipation twice than the uniform composite. Moreover, 3D filler network outperforms 2D network, showing that the higher network dimension is conducive to multidirectional heat transfer. With a low filler consumption while higher design flexibility, this new composite material design and manufacturing approach overcomes restriction caused by filler loading.

Grain-size dependent electric-field induced structural changes and its role in determining the piezoelectric response of 0–3 piezoceramic-polymer composite

Polymer-piezoceramic 0–3 composites combine the flexibility of polymers and the excellent piezoelectric properties of ferroelectric based ceramics. While the grain size of ceramic powder is one of the important considerations in the fabrication of such composites, a correlation relating poling field induced structural changes and its possible influence on the overall piezoelectric response of the composite is still lacking. In this paper, we examine this issue on a 0–3 piezo-composite comprising ceramic powders of a low-lead piezoelectric alloy (x)Bi(Ni1/2Zr1/2O3-(1-x)PbTiO3 in the proximity of its morphotropic phase boundary and polyvinylidene fluoride as the polymer component. Composites were fabricated by fixing the volume fraction of the ceramic while varying the grain size. We found a non-monotonic variation in the piezo-response as a function of grain size. Structural analysis before and after poling of the piezo-composites revealed evidence of poling induced cubic-like to tetragonal irreversible transformation, the extent of which is dependent on the grain size. Our findings suggest that the non-monotonic grain size dependence of the composite's piezoelectric response is associated with inducing a coexistence of long ranged and short ranged ferroelectric domains in the ferroelectric grains of the composite by the poling field. Our observations contradict a conjecture reported in the past, which attributed a similar non-monotonic grain size dependent piezoelectric behavior to the larger grains becoming off-stoichiometric.

Organic-Inorganic Composites Toward Biomaterial Application.

Bioactive ceramics are known to exhibit specific biological affinities and are able to show direct integration with surrounding bone when implanted in bony defects. However, their inadequate mechanical properties, such as low fracture toughness and high Young's modulus in comparison to natural bone, limit their clinical application. Bone is a kind of organic-inorganic composite where apatite nanocrystals are precipitated onto collagen fibre networks. Thus, one way to address these problems is to mimic the natural composition of bone by using bioactive ceramics via material designs based on organic-inorganic composites. In this chapter, the current research on the development of the various organic-inorganic composites designed for biomaterial applications has been reviewed. Various compounds such as calcium phosphate, calcium sulphate and calcium carbonate can be used for the inorganic phases to design composites with the desired mechanical and biological properties of bone. Not only classical mechanical mixing but also coating of the inorganic phase in aqueous conditions is available for the fabrication of such composites. Organic modifications using various polymers enable the control of the crystalline structure of the calcium carbonate in the composites. These approaches on the fabrication of organic-inorganic composites provide important options for biomedical materials with novel functions.

Morphology-controlled ZnO nanowire arrays for tailored hybrid composites with high damping.

Hybrid fiber reinforced composites using a nanoscale reinforcement of the interface have not reached their optimal performance in practical applications due to their complex design and the challenging assembly of their multiscale components. One promising approach to the fabrication of hybrid composites is the growth of zinc oxide (ZnO) nanowire arrays on the surface of carbon fibers to provide improved interfacial strength and out of plane reinforcement. However, this approach has been demonstrated mainly on fibers and thus still requires complex processing conditions. Here we demonstrate a simple approach to the fabrication of such composites through the growth of the nanowires on the fabric. The fabricated composites with nanostructured graded interphase not only exhibit remarkable damping enhancement but also stiffness improvement. It is demonstrated that these two extremely important properties of the composite can be controlled by tuning the morphology of the ZnO nanowires at the interface. Higher damping and flexural rigidity of these composites over traditional ones offer practical high-performance composites.

An Interface‐Induced Co‐Assembly Approach Towards Ordered Mesoporous Carbon/Graphene Aerogel for High‐Performance Supercapacitors

Hierarchically porous composites with mesoporous carbon wrapping around the macroporous graphene aerogel can combine the advantages of both components and are expected to show excellent performance in electrochemical energy devices. However, the fabrication of such composites is challenging due to the lack of an effective strategy to control the porosity of the mesostructured carbon layers. Here an interface‐induced co‐assembly approach towards hierarchically mesoporous carbon/graphene aerogel composites, possessing interconnected macroporous graphene networks covered by highly ordered mesoporous carbon with a diameter of ≈9.6 nm, is reported. And the orientation of the mesopores (vertical or horizontal to the surface of the composites) can be tuned by the ratio of the components. As the electrodes in supercapacitors, the resulting composites demonstrate outstanding electrochemical performances. More importantly, the synthesis strategy provides an ideal platform for hierarchically porous graphene composites with potential for energy storage and conversion applications.

In Situ Growth of TiO2 in Interlayers of Expanded Graphite for the Fabrication of TiO2–Graphene with Enhanced Photocatalytic Activity

We present a facile route for the preparation of TiO(2)-graphene composites by in situ growth of TiO(2) in the interlayer of inexpensive expanded graphite (EG) under solvothermal conditions. A vacuum-assisted technique combined with the use of a surfactant (cetyltrimethylammonium bromide) plays a key role in the fabrication of such composites. Firstly, the vacuum environment promotes full infusion of the initial solution containing Ti(OBu)(4) and the surfactant into the interlayers of EG. Subsequently, numerous TiO(2) nanoparticles uniformly grow in situ in the interlayers with the help of the surfactant, which facilitates the exfoliation of EG under the solvothermal conditions in ethanol, eventually forming TiO(2)-graphene composites. The as-prepared samples have been characterized by Raman and FTIR spectroscopies, SEM, TEM, AFM, and thermogravimetic analysis. It is shown that a large number of TiO(2) nanoparticles homogeneously cover the surface of high-quality graphene sheets. The graphene exhibits a multi-layered structure (5-7 layers). Notably, the TiO(2)-graphene composite (only 30 wt % of which is TiO(2)) synthesized by subsequent thermal treatment at high temperature under nitrogen shows high photocatalytic activity in the degradation of phenol under visible and UV lights in comparison with bare Degussa P25. The enhanced photocatalytic performance is attributed to increased charge separation, improved light absorbance and light absorption width, and high adsorptivity for pollutants.

Mechanisms of nonionic polymer adsorption on oxide surfaces

Oxide particles are commonly used as fillers in plastics, paper, rubber, etc. (particulate composites). The successful fabrication of such composites is dependent upon the adhesive strength of the filler particles to the matrix. The compatibility of the matrix and the filler particles is generally enhanced by the adsorption of surface modifiers such as surfactants and polymers at the particle-matrix interface. To develop a scientific basis for the selection of the appropriate modifiers it is necessary to understand their adsorption mechanisms. Specifically, the adsorption of polymeric additives is attributed to a combination of chemical and electrostatic interactions, hydrogen bonding and van der Waals forces. Hydrogen bonding has been suggested to be the primary adsorption mechanism for nonionic polymers. However, a literature survey of the Poly(ethylene oxide) (PEO)-oxide system suggested that PEO, a nonionic polymer, was substrate specific. A systematic study was undertaken to investigate the adsorption mechanisms of PEO on oxide particles. It was determined that strong Bronsted acid sites on the surface interact with the ether oxygen, a Lewis base, of PEO to induce adsorption. In this work, characterization of PEO binding sites on oxides is reported and the mechanisms of PEO adsorption are discussed.

The compressive behaviour of three-phase composite tubes

This paper describes the results of tests on a series of multi-phase composite tubes fabricated from carbon-fibre-reinforced epoxy resin interleaved with metallic foils. The object of the programme was to investigate the problems in the fabrication of such composites, and the behaviour characteristics under compressive loads. Failures were due to structural instability, and on the basis of the observed failure mode, a theory is proposed to predict ultimate loads.