Balancing Dielectric Loss and Magnetic Loss in Fe-NiS2/NiS/PVDF Composites toward Strong Microwave Reflection Loss.

Lightweight, broad-band, and highly efficient microwave-absorbing materials (MAMs) with tunable electromagnetic properties are in high demand. However, the absorption properties are limited by the simple loss mechanism in commonly used absorbing materials. Here, we tested the microwave-absorbing properties of Fe-NiS2/NiS/poly(vinylidene fluoride) (PVDF) in the frequency range of 2-18 GHz. For the 2.5% Fe-NiS2/NiS/PVDF with the filling content of 20 wt %, the maximum reflection loss can reach -61.72 dB at 14.88 GHz, and the bandwidth can reach 3.8 GHz with the reflection loss value below -10 dB. Loss mechanisms of different composites were analyzed on the basis of their magnetic and dielectric properties using both experimental and computational methods. The results indicate that strong microwave absorption property is achieved through a balancing of dielectric loss and magnetic loss. These findings present a new strategy for the future design of MAMs.

Design, Fabrication and Characterization of Pressure-Responsive Films Based on The Orientation Dependence of Plasmonic Properties of Ag@Au Nanoplates.

A novel pressure-responsive polymer composite film was developed based on Ag@Au composite nanoplates (NPLs) and polyvinylpyrrolidone (PVP) by using Au nanoparticles as concentration reference. The orientation change of Ag@Au NPLs is impelled by the deformation of polymer matrix under pressure, resulting in its localized surface plasmon resonance (LSPR) intensity change of in-plane dipolar peak. The intensity ratio between plasmon peak of Au nanoparticles and in-plane dipolar peak of Ag@Au NPLs relies on the intensity and duration of pressure. By adjusting the viscosity of the polymer, the orientation change of LSPR may respond to a wide range of stresses. This pressure sensitive film can be utilized to record the magnitude and distribution of pressure between two contacting surfaces via optical information.

Aqueous solution synthesis of CaF2 hollow microspheres via the ostwald ripening process at room temperature.

Nearly monodispersive CaF2 hollow microspheres were synthesized by a facile aqueous solution route from the mixed aqueous solutions of CaCl2, Na2WO4, and NaF at room temperature. The as-prepared products were characterized by X-ray diffraction (XRD), scanning electron microscopy, transmission electron microscopy (TEM), high-resolution transmission electron microscopy, and N2 adsorption-desorption techniques. The CaF2 hollow microspheres have an average diameter of about 1.5 microm and a hollow interior of 0.5 microm. The shell is composed of numerous single-crystalline nanoparticles with diameter of about 20 nm. The morphologies and diameters of the CaF2 products are strongly dependent on the experimental parameters, such as the concentration of the aqueous NaF solution and the reaction temperature. The synthetic experiments indicate that the growth process of CaF2 hollow microspheres involves first the formation of CaWO4 solid microspheres and then the formation of CaF2 solid microspheres through the reaction between CaWO4 and F(-) ions controlled by the difference of the solubility product for CaWO4 and CaF2. Phenomenological elucidation based on TEM observations and XRD patterns of intermediate products at different precipitation stages indicates that the formation mechanism for the CaF2 hollow microspheres is related to the Ostwald ripening mechanism. N2 adsorption-desorption measurement shows that the CaF2 hollow microspheres possess a high Brunauer-Emmett-Teller surface area and porosity properties. The synthetic procedure is straightforward and represents a new example of the Ostwald ripening mechanism for the formation of inorganic hollow structures in an aqueous solution at room temperature.

Room temperature synthesis of hollow CdMoO(4) microspheres by a surfactant-free aqueous solution route.

Hollow cadmium molybdate microspheres have been successfully prepared via a template-free aqueous solution method with the assistance of NaCl at room temperature. The structure and morphology of the CdMoO(4) hollow microspheres were characterized by X-ray diffraction, field-emission scanning electron microscopy, and transmission electron microscopy. The microspheres have diameters of 3-6 microm and hollow interiors of 2-3 microm. The shell is composed of numerous single-crystalline nanorods with diameters of 30-120 nm and lengths of 1-2 microm which are radially oriented to the center. A certain concentration of NaCl plays a key important role in the formation process of hollow microspheres, which might provide a suitable chemical environment to favor the formation of hollow CdMoO(4) microspheres. A possible NaCl-induced Ostwald ripening process is proposed for the formation of hollow CdMoO(4) microspheres on the basis of scanning electron microscopy observation of intermediate products at different precipitation stages.