Zaoming Wang

Towards efficient microwave absorption: intrinsic heterostructure of fluorinated SWCNTs

The construction of heterostructures is always effective to achieve efficient microwave absorption (MA) properties. Herein, different from conventional hybrid techniques, a novel microwave absorber with an intrinsic heterostructure is fabricated via direct heating fluorination of SWCNTs (F-SWCNTs) utilizing F2/N2. The as-prepared inhomogeneous F-SWCNTs are confirmed to contain both fluorinated domains and aromatic domains at the nanoscale. The evolution of the fluorinated domains is closely related to the development of the C–F groups, whereas the –CF2 groups have no effect. For MA, it is proposed that the aromatic domains function as attenuation regions, whereas the fluorinated domains serve as microwave transparent regions. When the area of aromatic domains is almost equal to that of fluorinated domains, the complementarity between attenuation ability and impedance match endows F-SWCNTs (fluorine content equals of 6.8%) with a good MA performance. Specifically, with only 4.8 wt% loading, the minimum reflection loss (RL) reaches −64.3 dB at the thickness of 1.61 mm, and the effective absorption region (RL < −10 dB) covers a range of 14.1–18 GHz at the thickness of 1.15 mm. The MA performances rely on the evolution of the physical heterostructure, instead of the introduced chemical bonds or fluorine-containing functional groups. The simplicity and feasibility of our design concept indicate the potential application of F-SWCNTs industrially.

Skin–core structured fluorinated MWCNTs: a nanofiller towards a broadband dielectric material with a high dielectric constant and low dielectric loss

This paper presents a novel skin–core structured multiwalled carbon nanotube (MWCNTs) nanofiller to enhance the dielectric performance of epoxy resin through selective fluorination of the outer shell of the MWCNTs. The outer fluorinated shells not only guarantee good dispersibility of the fluorinated MWCNTs (F-MWCNTs) in epoxy, but also prevent the direct contact of the conductive inner tubes. As a result, the inner tubes in adjacent F-MWCNTs can form abundant microcapacitors, leading to an obvious improvement of the dielectric constant of the epoxy resin with low dielectric loss. When the filler content is 8 wt%, the dielectric constant of the F-MWCNTs/epoxy composite varies from 57 at 100 Hz to 44.9 at 1 MHz, about 11.9 times and 10.8 times that of neat epoxy resin, respectively. Simultaneously, the dielectric loss maintains low values of 0.043 at 100 Hz and 0.036 at 1 MHz, respectively. The broadband high-κ and low dielectric loss demonstrate the frequency-stable dielectric behavior of the F-MWCNTs/epoxy composites, which is attributed to the suppression of the space charge polarization induced by the grafting of the strongly electronegative element fluorine onto the outer shell. We believe that the convenient preparation process and special structure will provide a new design for fabricating broadband high-κ dielectric materials with low dielectric loss.