Anisotropic Composites Research Articles

Transport Properties and Structure of Anisotropic Composites Based on Cation-Exchange Membranes and Polyaniline

Transport Properties and Structure of Anisotropic Composites Based on Cation-Exchange Membranes and Polyaniline

Anisotropic Shape Memory Composite for Dynamically Adjustable Electromagnetic Interference Shielding

Smart electromagnetic interference (EMI) shielding materials that enable dynamical adjustment of electromagnetic wave transmission are highly desirable for various applications. Nevertheless, ordinary materials show nonadjustable EMI shielding performance after deployment. Herein, an anisotropic smart EMI shielding composite is presented, which shows tunable EMI shielding effectiveness by rotation, shape memory, and simple stacking. The composite possesses a sandwich structure consisting of two graphene fibrous films (GFFs) with intermediate shape memory poly(ethylene-co-vinyl acetate) (EVA). Owing to the aligned graphene fibers of GFF, the GFF/EVA composite showed anisotropic mechanical property, shape memory property, and shielding effectiveness. The composite shows high tensile strength but declined shape memory property in the axial direction (0°) of the graphene fibers. In the 0° direction of the GFF/EVA composite, a total shielding effectiveness (SET) of >40.8 dB in the X-band is observed, which is much higher than that in the 90° direction (vertical, <8.1 dB). The rotation-modulated EMI shielding of GFF/EVA is achieved by the anisotropy-dependent EMI shielding performance. Moreover, tunable EMI shielding is demonstrated through the shape memory process of the composite and the average SET can be adjusted in the range from 43.2 to 33.1 dB by fixing a tensile strain from 0 to 100%. Furthermore, the EMI shielding of the multilayered composite can be modulated by stacking individual GFF/EVA composites at different angles. The smart GFF/EVA composite with tunable and function-switchable features is demonstrated, which will contribute to the development of smart EMI shielding materials and devices for electromagnetic applications in various fields.

Additive manufacturing of anisotropic graphene-based composites for thermal management applications

Additive manufacturing of anisotropic graphene-based composites for thermal management applications

Transport Properties and Structure of Anisotropic Composites Based on Cation Exchange Membranes and Polyaniline

A comprehensive characterization of basic heterogeneous cation-exchange MK-40 and Ralex CMH membranes and composite membranes with polyaniline based on them was performed, including the determination of conductivity and diffusion permeability, measurement of current–voltage curves in solutions of sodium, calcium, magnesium chlorides and hydrochloric acid, distribution curves of water binding energy and effective pore radii, as well as an assessment of the transport-structural parameters of microheterogeneous model. The time of polyaniline synthesis on the surface of cation-exchange membranes by successive diffusion of an oxidizing agent and monomer solution through the membrane into water was determined. Samples with an anisotropic structure and asymmetric electrotransport properties were obtained. Based on the analysis of the electrotransport properties, structure characteristics and model transport-structural parameters of membranes in solutions of singly and doubly charged ions, the obtained materials were defined as promising for use in the processes of electrodialysis desalination of multicomponent solutions.

Functionally graded structure design for magnetic field applications

This study presents topology optimization methodology of anisotropic magnetic composites, which consist of two ferromagnetic materials with low and high reluctivity values, considering the nonlinear magnetic saturation effect. Instead of employing the asymptotic homogenization theory, the representative volume element method combined with the machine learning is used to build the continuous function model and it is applied to obtain the material property according to the design variable change. Finally, the micro-scale functionally graded structure composed of two ferromagnetic materials with the macro-scale topological morphology is simultaneously designed to improve the magnetic performance of actuators. Numerical examples for symmetric and asymmetric magnetic actuator models are provided to validate the effectiveness of proposed design process. In the numerical results, optimized configurations and objective values obtained with the nonlinear magnetic composite material, which depend on the intensity of the magnetic flux density, are compared with those of the linear magnetic composite material.

Remarkable Conductive Anisotropy of Ag-Coated Glass Microbeads/UV Adhesive Composites Made by Electric Field Induced Alignment

We successfully prepared highly anisotropic conductive composites (ACCs) made of Ag-coated glass microbeads/UV adhesive via electric field-induced alignment, which was achieved using custom patterned microelectrode arrays. An optimized AC electric field (2 kV/cm, 1 kHz) with pole-plate spacing (50 μm) was utilized to effectively assemble the microbeads into chain arrays, which were precisely positioned on the microelectrode arrays to construct ordered conductive channels. In this case, tangling and cross-connection of the assembled microchains could be reduced, resulting in enhanced performance of the ACCs with high conductivity as well as excellent anisotropy. With a minor loading (3 wt %), the conductivity in the alignment direction could reach ∼24.9 S/m, which was the highest among the reported ACCs to the best of our knowledge, and it could also be 6 orders of magnitude higher than that within the plane. Besides, the samples exhibited high reliability in wire connections with low resistances. Due to these fascinating properties, the ACCs demonstrate promising applications for reliable electrical interconnects and integrated circuits.

A probabilistic framework for source localization in anisotropic composite using transfer learning based multi-fidelity physics informed neural network (mfPINN)

The practical application of data-driven frameworks like deep neural network in acoustic emission (AE) source localization is impeded due to the collection of significant clean data from the field. The utility of the such framework is governed by data collected from the site and/or laboratory experiment. The noise, experimental cost and time consuming in the collection of data further worsen the scenario. To address the issue, this work proposes to use a novel multi-fidelity physics-informed neural network (mfPINN). The proposed framework is best suited for the problems like AE source detection, where the governing physics is known in an approximate sense (low-fidelity model), and one has access to only sparse data measured from the experiment (high-fidelity data). This work further extends the governing equation of AE source detection to the probabilistic framework to account for the uncertainty that lies in the sensor measurement. The mfPINN fuses the data-driven and physics-informed deep learning architectures using transfer learning. The results obtained from the data-driven artificial neural network (ANN) and physics-informed neural network (PINN) are also presented to illustrate the requirement of a multi-fidelity framework using transfer learning. In the presence of measurement uncertainties, the proposed method is verified with an experimental procedure that contains the carbon-fiber-reinforced polymer (CFRP) composite panel instrumented with a sparse array of piezoelectric transducers. The results conclude that the proposed technique based on a probabilistic framework can provide a reliable estimation of AE source location with confidence intervals by taking measurement uncertainties into account.

Anisotropic Heavy-Metal-Free Semiconductor Nanocrystals: Synthesis, Properties, and Applications.

Heavy-metal (Cd, Hg, and Pb)-containing semiconductor nanocrystals (NCs) have been explored widely due to their unique optical and electrical properties. However, the toxicity risks of heavy metals can be a drawback of heavy-metal-containing NCs in some applications. Anisotropic heavy-metal-free semiconductor NCs are desirable replacements and can be realized following the establishment of anisotropic growth mechanisms. These anisotropic heavy-metal-free semiconductor NCs can possess lower toxicity risks, while still exhibiting unique optical and electrical properties originating from both the morphological and compositional anisotropy. As a result, they are promising light-emitting materials in use various applications. In this review, we provide an overview on the syntheses, properties, and applications of anisotropic heavy-metal-free semiconductor NCs. In the first section, we discuss hazards of heavy metals and introduce the typical heavy-metal-containing and heavy-metal-free NCs. In the next section, we discuss anisotropic growth mechanisms, including solution-liquid-solid (SLS), oriented attachment, ripening, templated-assisted growth, and others. We discuss mechanisms leading both to morphological anisotropy and to compositional anisotropy. Examples of morphological anisotropy include growth of nanorods (NRs)/nanowires (NWs), nanotubes, nanoplatelets (NPLs)/nanosheets, nanocubes, and branched structures. Examples of compositional anisotropy, including heterostructures and core/shell structures, are summarized. Third, we provide insights into the properties of anisotropic heavy-metal-free NCs including optical polarization, fast electron transfer, localized surface plasmon resonances (LSPR), and so on, which originate from the NCs' anisotropic morphologies and compositions. Finally, we summarize some applications of anisotropic heavy-metal-free NCs including catalysis, solar cells, photodetectors, lighting-emitting diodes (LEDs), and biological applications. Despite the huge progress on the syntheses and applications of anisotropic heavy-metal-free NCs, some issues still exist in the novel anisotropic heavy-metal-free NCs and the corresponding energy conversion applications. Therefore, we also discuss the challenges of this field and provide possible solutions to tackle these challenges in the future.

Impact Localization in Anisotropic Composites With Time Difference Matrix Matching and Edge Accuracy Optimization

Composites play an important role in the development of modern science and technology, but the special anisotropy leads to difficulties in impact localization. To achieve impact localization on composite materials, this paper proposes a time difference matrix matching method with edge accuracy optimization. The method uses the propagation characteristics of Lamb wave in composite materials to solve the direction dependence of wave velocity. To overcome the anisotropy, the time difference feature vector of each element of the composite material is obtained by grid division, and the impact location is found according to the similarity. In addition, edge accuracy optimization is proposed to further improve localization accuracy. Using 49 points in the 800mm×800mm composite area for 147 impact tests, the result shows that the average error can reach 0.532cm, and the variance is 0.217cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> .

Correlation of Light Polarization in the Magnetic Media with Non-Spherical Point-Like Inclusions

Light propagation through magnetic media with ellipsoidal inclusions much smaller than the light wavelength was investigated theoretically. It is assumed that the ellipsoidal inclusions have the same orientation but are randomly distributed inside the magnetic medium by the Gaussian law. The theoretical model is based on the multiple-scattering theory in the ladder approximation. A new type of electromagnetic field correlation is found to appear in this case, while it is absent in isotropic magnetic nanocomposites and nonmagnetic anisotropic composites. This feature allows for the precise control of light polarization in anisotropic magnetic media.

Anisotropic nucleation and compatibilization of SiO2@PS Janus particles on expandable polystyrene

Inorganic particles usually used as nucleation agent to promote the polymer foaming of supercritical carbon dioxide. However, they are apt to agglomerating in the matrix, which is not conducive to obtaining foamed materials with homogeneous cells. Herein, the organic-inorganic Janus particles possess anisotropic chemical compositions were introduced into expandable polymer, in which two sides can perform compatibilization and nucleation independently. The dispersion of silica@polystyrene (SiO2 @PS) Janus particles (JPs) in PS matrix and the resulting improvements in rheological property, foaming performance, compressive strength of PS was discussed systematically. JPs could be uniformly dispersed in PS matrix attributed to the PS end of JPs. While the SiO2 end of JPs could act as heterogeneous nucleation agent and promote cell formation. Compared with PS foams, PS/JPs foams had smaller and more uniform cell sizes, leading to better compressive properties, i.e. the compressive strength of PS/JPs-5% foams at 100 °C, 110 °C and 120 °C increased by 37.4%, 60.6% and 57.9%, respectively. This work demonstrates that JPs are a novel nucleation and compatibilizer for making polymer foams with optimal cell structure and compressive property.

Molten-State Dielectrophoretic Alignment of EVA/BaTiO3 Thermoplastic Composites: Enhancement of Piezo-Smart Sensor for Medical Application.

Dielectrophoresis has recently been used for developing high performance elastomer-based structured piezoelectric composites. However, no study has yet focused on the development of aligned thermoplastic-based piezocomposites. In this work, highly anisotropic thermoplastic composites, with high piezoelectric sensitivity, are created. Molten-state dielectrophoresis is introduced as an effective manufacturing pathway for the obtaining of an aligned filler structure within a thermoplastic matrix. For this study, Poly(Ethylene-co Vinyl Acetate) (EVA), revealed as a biocompatible polymeric matrix, was combined with barium titanate (BaTiO3) filler, well-known as a lead-free piezoelectric material. The phase inversion method was used to obtain an optimal dispersion of the BaTiO3 within the EVA thermoplastic matrix. The effect of the processing parameters, such as the poling electric field and the filler content, were analyzed via dielectric spectroscopy, piezoelectric characterization, and scanning electron microscopy (SEM). The thermal behavior of the matrix was investigated by thermogravimetric analysis (TGA) and differential scanning calorimetry analysis (DSC). Thermoplastic-based structured composites have numerous appealing advantages, such as recyclability, enhanced piezoelectric activity, encapsulation properties, low manufacturing time, and being light weight, which make the developed composites of great novelty, paving the way for new applications in the medical field, such as integrated sensors adaptable to 3D printing technology.

Anisotropic cellulose nanocrystal composite hydrogel for multiple responses and information encryption

Anisotropic composites based on well-ordered cellulose nanocrystals (CNCs) have received increasing attention due to their fascinating optical properties. In this study, we fabricated a multi-functional hydrogel with nematic organization of CNC by soaking a pre-stretched polyvinyl alcohol (PVA)/CNC cyrogel in Na2SO4, CaCl2 solution and DI water in sequence. The crystalline domains, water content and transmittance of the hydrogel are regulated via the Hofmeister effect and hydrophobic interactions, which makes the birefringence of the hydrogel observable by interference colors. The aligned CNC not only enhance the mechanical strength of hydrogel, but also endow it with stimuli-responsive ability to the varying environment such as ion strength (0 to 5 M NaCl solution) and external forces (pressure of 0 to 248 kPa). Moreover, the patterned hydrogels are successfully fabricated by the method of local solvent displacement. Due to the low light transmission, the pattern can be encrypted and only be observed between crossed polarizers. These optical properties made the hydrogel a promising candidate for environmental monitoring and anti-counterfeit material.

Electrical performance of orthotropic and isotropic 3YTZP composites with graphene fillers

3 mol% yttria tetragonal zirconia polycrystal (3YTZP) composites with orthotropic or isotropic microstructures were obtained incorporating few layer graphene (FLG) or exfoliated graphene nanoplatelets (e-GNP) as fillers. Electrical conductivity was studied in a wide range of contents in two configurations: perpendicular (σꓕ) and parallel (σ//) to the pressing axis during spark plasma sintering (SPS). Isotropic e-GNP composites presented excellent electrical conductivity for high e-GNP contents (σꓕ ∼ 3200 S/m and σ// ∼ 1900 S/m for 20 vol% e-GNP), consequence of their misoriented distribution throughout the matrix. Optimum electrical performance was achieved in the highly anisotropic FLG composites, with high electrical conductivity for low contents (σꓕ ∼ 680 S/m for 5 vol%), percolation threshold below 2.5 vol% FLG and outstanding electrical conductivity for high contents (σꓕ ∼ 4000 S/m for 20 vol%), result of the high aspect ratio and low thickness of FLG.

Flask-like Janus Colloidal Motors with Explicit Direction and Tunable Speed.

Nanoparticles with an anisotropic morphology and composition are flourishing in various scientific fields. Their morphology has a great impact on their functions, but the precise regulation of their growth and final morphology is still challenging. Here, flask-like Janus particles (FJPs) with different compositions segmented on the inner and outer surfaces were fabricated via a sol-gel process using different silane precursors. The neck length of the flask-like particles can be controllably regulated by employing different silane precursors. The Pt catalyst was selectively loaded in their cavities, and as-formed FJPs@Pt are employed as colloidal motors. Due to the adjustable neck length, the Janus colloidal motors have explicit directionality and tunable speeds (max diffusion coefficient is 18.2 μm2 s-1).

Polymer-bonded magnets produced by laser powder bed fusion: Influence of powder morphology, filler fraction and energy input on the magnetic and mechanical properties

Bonded permanent magnets are key components in many energy conversion, sensor and actuator devices. These applications require high magnetic performance and freedom of shape. With additive manufacturing processes, for example laser powder bed fusion (LPBF), it is possible to produce bonded magnets with customized stray field distribution. Up to now, most studies use spherical powders as magnetic fillers due to their good flowability. Here, the behavior of large SmFeN platelets with a high aspect ratio as filler material and its influence on the arrangement and the resulting magnetic properties are examined in comparison to a spherical magnetic filler. The 3D distribution and orientation of the magnetic filler was studied by computed tomography and digital image analysis. The platelet-shaped particles align themselves perpendicular to the buildup direction during the process, which offers a new and cost-effective way of producing composites by LPBF with anisotropic structural and functional properties. The influence of LPBF parameters on the properties of the composites is investigated. Highest filling fractions are required for high magnetic remanence, however the powder itself limits this maximum due to particle shape and required minimal polymer fraction to form mechanically stable magnets. The coercivity decreases for higher filling fractions, which is attributed to increased rotation of insufficiently embedded magnetic particles in the matrix. It is discussed how filler morphology influences the observed change in coercivity since the rotation of spherical particles in comparison to platelet-shaped particles requires less energy. Our work shows the challenges and opportunities of large platelet shaped fillers used in LPBF for the production of anisotropic functional and structural composites.

Damage imaging method for composites laminates based on sparse reconstruction of single-mode Lamb wave

To address the problems of anisotropy and mode mixing in damage imaging on anisotropic composites laminates using ultrasonic Lamb wave, a sparse reconstruction imaging method based on S0 single-mode is proposed in this paper. In this approach, the sparsely arranged piezoelectric ceramic drivers sensor group on the surface of the measured composite laminate is employed to excite and receive Lamb wave. The received signal shows sparse under a pre-built damage dictionary with damage scattering signal waveform, and the damages can be localized and imaged using a sparse reconstruction method. Considering the velocity difference between S0 and A0 mode of the received Lamb wave signal, the S0 mode is extracted by intercepting the signal before the peak of the first wave packet to eliminate the influence of Lamb wave mode mixing. In order to minimize the influence of anisotropy of composites laminates on Lamb wave propagation, the Lamb wave propagation direction is divided evenly into several sectors, and Lamb wave propagation direction within a certain sector is considered as propagation in a quasi-isotropic material. The sparse reconstruction is solved by using the basis pursuit de-noising algorithm, which can find the optimal solution with a small number of iterations in noise interference. The experiments on composite fiber laminate specimens show that the proposed method can accurately locate simulated single delamination damage and has less artifact interference compared to the delay-and-sum method.

A measure of complexity for axial self-gravitating static fluids

One of the feasible potential candidates for illustrating the accelerating expansion of the cosmos can be taken through the notion of modified gravity. Within the context of metric f(R) gravity, the contribution of this work features a better understanding of complexity factors for anisotropic static fluid composition in axially symmetric spacetime. This is a generalization of the work done by Herrera et al (2019, Phys. Rev. D 99, 044 049). We formulate generalized dynamical and field equations for anisotropic sources in our analysis. We will compute three distinct complexity factors (Y TF1, Y TF2, Y TF3) after incorporating structure scalars via orthogonal breakdown of the curvature tensor. The differential equations for the conformal tensor are assessed in terms of these complexity factors for the physical illustration. It is inferred that all these factors vanish for the matter spheroid provided with energy homogeneity and isotropic pressure. Nonetheless, the vanishing of these factors might be observed in different scenarios. This happened because energy inhomogeneity and pressure anisotropy cancel out each other in the description of complexity factors. Certain exact solutions of this nature have been reported and studied. All of the outcomes would reduce to general relativity within usual limits.

Giant magnetostriction in low-concentration magnetorheological elastomers

Magnetorheological elastomers (MREs) are smart composite materials that can vary their mechanical properties under the influence of an external magnetic field. In the present work, we report the giant magnetostriction of low-concentration isotropic and anisotropic MREs, by combining a soft elastomer matrix with helicoidal-shaped particles. Magnetic characterization has shown high magnetic sensitivity of the anisotropic MREs near H ≅ 0, which can be up to 400% larger comparing to the isotropic counterparts. The determination of tensile elastic modulus (E) of the MREs indicates that the anisotropic samples become softer when the magnetic field is increased from H = 0 to H = 200 Oe. Due to the higher field sensitivity of the anisotropic composites, the magneto-induced elongation contributes to the increase in the overall strain when measuring the elastic modulus at low deformation. This compliance of the MRE explains the decrease in E from H = 0 to H = 200 Oe. Magnetostriction measurements were performed and giant strain values up to 3731 ppm were obtained for isotropic samples with 3.4 vol% of Hiperco particles under a field of H = 3500 Oe. This result stands out from the literature due to the giant induced elongation, with reduced volume fraction of particles. The developments of this work are a step forward on improving smart and efficient composites, that can have many applications, such as switches, controllable valves, and vibration attenuators.

Rapid synthesis of biocompatible bilayer hydrogels via frontal polymerization

AbstractHydrogels have been attracting much attention as smart soft materials. The exploration of methods allowing hydrogels to have anisotropic composition, structure, and properties would benefit the fabrication of smart materials with versatile multi‐functions. Here we report the rapid frontal polymerization (FP) of bilayer hydrogels possessing good water swelling, mechanical strength, self‐healing, biocompatibility, and antibacterial capabilities. The bilayer hydrogels, consisting of poly(AM‐co‐AMPS) (G‐1) and poly(AM‐co‐HPA) (G‐2) (AM, acrylamide; AMPS, 2‐acrylamide‐2‐methylpropanesulfonic acid; HPA, hydroxypropyl acrylate), are synthesized in one step within 6 minutes (min) by horizontal FP. These polymer hydrogels have hierarchical porous morphology with pore sizes of several micrometers and several hundreds of micrometers respectively, equilibrium swelling ratio up to 3371% in water, tensile strength up to 0.204 MPa, and self‐healing ability. The good cytocompatibility and low toxicity of the hydrogels are demonstrated through cell culture of L929 fibroblasts in vitro experiments. The tests of hydrogels with Escherichia coli and Staphylococcus aureus reveal their antibacterial property. The results demonstrate that biocompatible anisotropic hydrogels with versatile functions could be fabricated via the rapid and energy‐saving approach of FP.