Highly uniform core-shell composites, polypyrrole@polyaniline (PPy@PANI), have been successfully constructed by directing the polymerization of aniline on the surface of PPy microspheres. The thickness of PANI shells, from 30 to 120 nm, can be well controlled by modulating the weight ratio of aniline and PPy microspheres. PPy microspheres with abundant carbonyl groups have very strong affinity to the conjugated chains of PANI, which is responsible for the spontaneous formation of uniform core-shell microstructures. However, the strong affinity between PPy microspheres and PANI shells does not promote the diffusion or reassembly of two kinds of conjugated chains. Coating PPy microspheres with PANI shells increases the complex permittivity and creates the mechanism of interfacial polarization, where the latter plays an important role in increasing the dielectric loss of PPy@PANI composites. With a proper thickness of PANI shells, the moderate dielectric loss will produce well matched characteristic impedance, so that the microwave absorption properties of these composites can be greatly enhanced. Although PPy@PANI composites herein consume the incident electromagnetic wave by absolute dielectric loss, their performances are still superior or comparable to most PANI-based composites ever reported, indicating that they can be taken as a new kind of promising lightweight microwave absorbers. More importantly, microwave absorption of PPy@PANI composites can be simply modulated not only by the thickness of the absorbers, but also the shell thickness to satisfy the applications in different frequency bands.

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The possibility of laser cooling of bismuth hydride (BiH) molecules has been investigated based on high-level ab initio calculations by considering the core-valence and the spin-orbit coupling (SOC) effects. The potential energy curves of the 12 Λ-S states as well as the 25 Ω states that split from them via SOC are obtained by multireference configuration interaction plus the Davidson correction. The properties of b-X transition are investigated. Based on our calculations, we show that the transition between Ω states b0+–X10+ of BiH is a possible candidate for laser cooling, with consideration of the intermediate Ω state X21. An optical cycling scheme is proposed by utilizing four lasers at wavelengths around 471 and 601 nm with 5400 cycles for photon absorption/emission and a sub-microkelvin temperature. Our study should shed some light on searching for possible molecular candidates for laser cooling with the existence of an intermediate electronic state.

Rational design of the microstructure paves new ways for microwave absorbing materials because it can create more facilities for the attenuation of incident electromagnetic waves. In this study, a simple method is proposed to prepare yolk-shell carbon microspheres through differential shrinkage in the internal cores and external shells of polypyrrole microspheres with the assistance of outermost SiO2 coating. This method simplifies the preparation procedures and avoids strictly controlled conditions. The electromagnetic parameters, such as relative complex permittivity and permeability, of the as-prepared yolk-shell carbon microspheres, are investigated in the frequency range of 2.0–18.0 GHz. Compared with solid carbon microspheres, yolk-shell carbon microspheres exhibit significantly enhanced microwave absorption properties in terms of both the reflection loss intensity and absorption bandwidth. The minimum reflection loss value can reach up to −27.5 dB at 8.32 GHz with an absorber thickness of 2.96 mm. The absorption bandwidth over −10.0 dB is in the range of 11.3–16.2 GHz at the typical thickness of 2.0 mm. The enhanced microwave absorption properties may be attributed to the good attenuation ability and well matched characteristic impedance. This work not only provides a promising candidate for microwave absorption, but also provides an attractive strategy to prepare various yolk-shell composites.

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