Controllable construction of Fluorine-Contained phase region induced by fluorination phase Transformation: Towards enhanced microwave absorption of carbon foam

Towards enhancing microwave absorption (MA) performance of microwave absorbers, constructing multicomponent structure with heterogeneous interface structure are the commonly adopted strategies. Herein, we proposed a different idea to modify the MA property of carbon foam sheets (CFSs) by constructing phase region structure through direct fluorination utilizing F-2/N-2. The fluorination of CFSs obey a phase expanding model, which starts at defect sites, and subsequently expands to neighboring aromatic benzene ring. As a result, the fluorination process experienced phase transformation from "discrete fluorine (F)-contained" phase region to "cluster F-contained" phase region and then to "expanded F-contained" phase region. With phase structure transforming, the dominated dissipation mechanism toward electromagnetic wave varied from dipole polarization to interfacial polarization, making the MA property of F-CFSs to be customized. For F-CFSs with "discrete F-contained" phase region, strong dipole polarization provided by discrete C-F bond would noticeably enhance the MA property around Ku band (RLmin similar to -66.6 dB, covering 65.3% of Ku band). By contrast, For F-CFSs with "cluster or expanded F-contained" phase region, interfacial polarization generated by countlessly atomic-level heterojunctions between fluorinated and aromatic region would improve the MA property around C band (RLmin similar to -66 dB, covering 76% of C band). Our work provided a new insight to enhance and customize microwave absorption for carbon based microwave absorbers.