Search

Microparticle rotation is an important process in biomedical engineering, such as biosensors, cell injection or cell morphology. Single particle rotation has been widely investigated, while rotation of particle chains has gained rare attention. In this paper, we utilize a noncontact manipulation method to rotate microparticle chains via electrorotation by designing an octuple-electrode array (OEA). Finite element simulations were conducted for analyzing the desired electrode field and optimizing the structure of microelectrode pairs. The direction of the electric field in the workspace is investigated with different voltage signal inputs through specially designed circuits. In the experiment, microparticles are driven to form several chains in the proposed electrode fields. With the rotation of the electric field, particle chains could be rotated synchronously. Automated rotation and detection of polystyrene microspheres and yeast cell chains are achieved using machine vision technology. Results show that the proposed method could be utilized to rotate ordered microparticles with an appropriate input signal. [ABSTRACT FROM AUTHOR]

High areal capacitance or energy density is still a challenging issue for carbon-based micro-supercapacitors (MSCs). Herein, porous carbon nanosheets with a unique polycrystalline-like micro-morphological feature (PL-PCN) are in situ constructed for the first time through a two-step fabrication strategy, which is realized by the synthesis of 2D polycrystalline titanium carbide (TiC) nanosheets (P–TiC) using graphene nanosheets (GNS) as the template and the subsequent high-temperature chlorination of P–TiC. Interestingly, the resultant PL-PCN has the characteristics of a high specific surface area (up to 1649.97 m2 g−1), superb wettability to electrolytes, and a unique hierarchical micro- and meso-porous structure, in which the mesopores existing in the form of "grain boundary" and the micropores inside the "grain" can effectively provide abundant ion transport channels and accessible electrochemically active sites, respectively. Arising from these advantages, the all-solid-state MSC built by using PL-PCN as the electrode material delivers exceptional electrochemical performances, such as an ultrahigh areal capacitance of 108.88 mF cm−2 and energy density of 14.73 μW h cm−2, both of which, to the best of our knowledge, are among the highest values reported so far for carbon-based MSCs. Furthermore, the fabricated MSC also possesses superb mechanical flexibility, and the capacitive output and voltage can be easily regulated by connecting multiple MSC devices in parallel and series. Hence, this work provides a new insight to design and fabricate a carbon electrode material for high-performance micro-supercapacitors. [ABSTRACT FROM AUTHOR]

Composite particles with multiple components and specific structures are promising microwave absorbents due to their excellent and easily tailored synergism of multiple dissipation mechanisms and good impedance matching, but their design and highly efficient preparation remain as big challenges. In the present work, novel composite carbon–FeNi alloy–nickel ferrite hollow microspheres with a thin shell were constructed through a highly efficient spray drying–calcination route. The amorphous carbon serves as the matrix of the shell, and the FeNi alloy and nickel ferrite form an embedded structure in the carbon shell. The design of this matrix–dual dispersion phase structure not only enables the synergism between the magnetic loss of the magnetic dispersion phase and the dielectric loss of the carbon matrix, but also brings multiple reflection and scattering, interface polarization as well as an appropriate impedance matching. Due to these features, the hollow microspheric product presents excellent microwave-absorbing properties related to the processing conditions (the optimized effective absorption bandwidth reaches 7.76 GHz at a thickness of 2.04 mm). The hollow microspheres reported here are a promising candidate for a microwave absorbent with low density and strong dissipation. [ABSTRACT FROM AUTHOR]

Due to their multiple dissipation mechanisms, low density and easily tailored impedance matching, heterogeneous hollow structures are promising candidates for microwave absorbents towards wideband absorption and lightweight design. In this work, a new type of hollow microspheres with a porous carbon shell embedded with crystalline FeCo alloy nanoparticles have been prepared via a stepwise spray drying–calcination strategy. The effects of both the FeCo/C molar ratio and the calcination temperature on the structure and property of the porous hollow microspheres (PHMs) have been studied. It is found that the effective absorption bandwidth of the as-prepared FeCo/C PHMs surpassed 7.44 GHz at a matching thickness of 2.64 mm, which covers the full Ku-band. Moreover, with an elevated calcination temperature, high microwave absorbing performance can be achieved at a much reduced matching thickness. A probable absorbing mechanism has been proposed involving the synergistic effect of the hollow interior, the porous shell structure, and the electric and magnetic dissipation due to the coexistence of carbon and magnetic metals. This work opens a new pathway to synthesize microwave absorbents with a heterogeneous hollow structure, and may shed some light on the design and controlled preparation of other hollow structures with various shell compositions. [ABSTRACT FROM AUTHOR]

Low density (ca. 0.69 g cm−3) sandwich structured silicate–CoNi–carbon triple shell composite hollow microspheres (CHMs) were prepared by a stepwise three-stage shell-assembly route. Hollow microspheres with robust silicate shells were fabricated firstly through spray drying-high temperature melting, which were subsequently employed as a support for the in situ formation and assembly of CoNi shells. Then the CoNi shells underwent a double-interface co-constricted crystallization during calcination-induced carbonization to form the final product. The density of the hollow microspheres increases gradually with the stepwise assembly of the CoNi and the carbon shells, while the broken ratio of the hollow microspheres at the same isostatic pressure varies in an opposite trend. Moreover, the enriched interfaces with distinguished conductivity, multiple electromagnetic dissipation mechanisms and suitable impedance matching favour the triple shell CHMs with excellent electromagnetic absorption properties. The minimum reflection loss value can reach −55.4 dB, and a broad effective frequency range of 6.8 GHz can be achieved. Moreover, when used as lightweight functional fillers, the as-obtained polymer-triple shell CHMs composite exhibits a low density of 0.92 g cm−3 and high compression strength of 132 ± 2.1 MPa. [ABSTRACT FROM AUTHOR]

Herein, we described photoenzymatic dynamic kinetic resolution (DKR) of amines under mild conditions. The racemization of amines via a photoredox-mediated hydrogen atom transfer (HAT) protocol in conjunction with an enzyme catalyst to achieve the DKR of amines allows a variety of primary amines to be converted into a single enantiomer in high yield and with excellent enantioselectivity. Notably, this protocol can also be extended to 1,4-diamine derivatives with high levels of diastereo- and enantioselectivity. [ABSTRACT FROM AUTHOR]

Composite shelly hollow particles with glass–iron oxide, glass–iron and glass–iron–carbon shells were prepared on a large scale through a stepwise strategy involving sol combustion assembly and controlled heat treatment. Micron-sized silicate glass hollow particles prepared in our previous work were used as the starting material to serve as the first shell with hollow interior. Then iron oxide and iron–carbon shells were assembled on the silicate glass shell by fast dehydration–combustion of a mixed sol containing iron resource, fuel and the preformed glass hollow particles in air and nitrogen atmospheres, respectively. Afterwards, the glass–iron oxide composite shelly hollow particles underwent a thermal reduction treatment to get metallic iron shells. The electromagnetic properties of the composite shelly hollow particles were studied and the results demonstrate that they present ferromagnetic properties and tunable microwave-absorbing performances related to the composition of the ferruginous shells. Owing to the synergism of appropriate magnetic and dielectric losses and enhanced interfacial effects, the glass–iron–carbon composite shelly hollow particles possess the best microwave-absorbing performance, in terms of both the minimum reflection loss (RL) value and the effective bandwidth, among the three kinds of products. Moreover, the as-obtained samples possess ultra-low density of 0.44, 0.46 and 0.51 g cm−3, respectively, for the glass–iron oxide, glass–iron and glass–iron–carbon composite shelly hollow particles, and may be promising candidates as low-density magnetic materials and microwave absorbents. [ABSTRACT FROM AUTHOR]

Silica–nickel–carbon composite microspheres with shelly hollow structures and tunable electromagnetic properties were prepared in large scale through a three-step route. Micron-sized precursor microspheres were prepared firstly by spray drying of water glass. Then a subsequent acid leaching with diluted hydrochloric acid was carried out to eliminate the Na2O in the precursor microspheres to get single shell silica hollow microspheres (SHMs). Afterwards, Ni–C composite shells were assembled on the surface of the previously formed SHMs through a calcination route in an inert atmosphere to form silica–nickel–carbon composite shelly hollow microspheres (CSHMs) through decomposition of the reactants and carbon thermal reduction. By properly tuning the calcination conditions, silica–nickel CSHMs with gradients in composition can also be prepared. The electromagnetic properties of the CSHMs were studied and the results demonstrate that they present ferromagnetic and microwave absorbing properties related to the shell composition. The DSHPs thus obtained may have some promising applications in the fields of low-density magnetic materials and microwave absorbers. This work provides a new strategy to fabricate shelly hollow particles, which can be expected to be extended to the controlled preparation of similar structures with various compositions. [ABSTRACT FROM AUTHOR]

Novel glass/Fe3O4core/shell composite hollow spheres with the shell layer assembled by multi-layered wafers were successfully synthesized by reduction of a glass/α-Fe2O3precursor, which was obtained through a facile solvothermal process. The effects of some reaction parameters on the morphology of the shell layers and the magnetic properties of the products were investigated. [ABSTRACT FROM AUTHOR]

Novel 3D urchin-like glass/Ni-Ni(3)P/Co(2)P(2)O(7) core/shell/shell composite hollow structures are fabricated for the first time by controlled stepwise assembly of granular Ni-Ni(3)P alloy and ribbon-like Co(2)P(2)O(7) nanocrystals on hollow glass spheres in aqueous solutions at mild conditions. It is found that the shell structure and the overall morphology of the products can be tailored by properly tuning the annealing temperature. The as-obtained composite core/shell/shell products possess low density (ca. 1.18 g cm(-3)) and shape-dependent magnetic and microwave absorbing properties, and thus may have some promising applications in the fields of low-density magnetic materials, microwave absorbers, etc. Based on a series of contrast experiments, the probable formation mechanism of the core/shell/shell hierarchical structures is proposed. This work provides an additional strategy to prepare core/shell composite spheres with tailored shell morphology and electromagnetic properties.

Novel urchin-like core/shell composite hollow spheres were fabricated by assembly of nickel nanocones on the surface of hollow glass spheres; the effects of some reaction parameters on the morphology of the shell layers and the room temperature magnetic properties of the products were investigated.