title: Tunable Microwave Absorption Frequency by Aspect Ratio of Hollow Polydopamine@α-MnO2 Microspindles Studied by Electron Holography.
abstract: A tunable response frequency is highly desirable for practical applications of microwave absorption materials but remains a great challenge. Here, hollow lightweight polydopamine@α-MnO2 microspindles were facilely synthesized with the tunable absorption frequency governed by the aspect ratio. The size of the hard template is a key factor to achieve the unique shape; the polymer layer with uniform thickness plays an important role in obtaining spindles with homogeneous size. With the aspect ratio increasing, the maximum reflection loss, as well as the absorption bandwidth (<-10 dB), increases and then decreases; meanwhile, the microwave absorption band shifts to the low frequency. The optimized aspect ratio of the cavity about the hollow polydopamine@α-MnO2 microspindles is ∼2.8. With 3 mm thickness at 9.7 GHz, the strongest reflection reaches -21.8 dB, and the width of the absorbing band (<-10 dB) is as wide as 3.3 GHz. Via electron holography, it is confirmed that strong charge accumulates around the interface between the polydopamine and α-MnO2 layers, which mainly contributes to the dielectric polarization absorption. This study proposes a reliable strategy to tune the absorption frequency via different aspect ratio polymer@α-MnO2 microspindles.
authors.affiliation: Laboratory of Advanced Materials, Department of Materials Science, Collaborative Innovation Center of Chemistry for Energy Materials, Fudan University , Shanghai 200438, China.
authors.forename: Wen
authors.initials: W
authors.lastname: She
authors.affiliation: Laboratory of Advanced Materials, Department of Materials Science, Collaborative Innovation Center of Chemistry for Energy Materials, Fudan University , Shanghai 200438, China.
authors.forename: Han
authors.initials: H
authors.lastname: Bi
authors.affiliation: Laboratory of Advanced Materials, Department of Materials Science, Collaborative Innovation Center of Chemistry for Energy Materials, Fudan University , Shanghai 200438, China.
authors.forename: Zhiwei
authors.initials: Z
authors.lastname: Wen
authors.affiliation: Laboratory of Advanced Materials, Department of Materials Science, Collaborative Innovation Center of Chemistry for Energy Materials, Fudan University , Shanghai 200438, China.
authors.forename: Qinghe
authors.initials: Q
authors.lastname: Liu
authors.affiliation: Laboratory of Advanced Materials, Department of Materials Science, Collaborative Innovation Center of Chemistry for Energy Materials, Fudan University , Shanghai 200438, China.
authors.forename: Xuebing
authors.initials: X
authors.lastname: Zhao
authors.affiliation: Laboratory of Advanced Materials, Department of Materials Science, Collaborative Innovation Center of Chemistry for Energy Materials, Fudan University , Shanghai 200438, China.
authors.forename: Jie
authors.initials: J
authors.lastname: Zhang
authors.affiliation: Laboratory of Advanced Materials, Department of Materials Science, Collaborative Innovation Center of Chemistry for Energy Materials, Fudan University , Shanghai 200438, China.
authors.forename: Renchao
authors.initials: R
authors.lastname: Che
keywords: aspect ratio; core−shell structure; dielectric loss; electron holography; manganese dioxide; microwave absorption; tunable frequency