Preparation of ultra-thin and flexible silver nanowires/reduced graphene oxide/cellulose nanofibers composite paper and its electromagnetic shielding properties
With the development of wireless communication technology,electromagnetic radiation pollution is becoming more and more serious.It is necessary to develop ultra-light,ultra-thin,flexible,and great mechanical properties electromagnetic shielding materials to protect precision electronic devices from electromagnetic radiation in-terference.Silver nanowires are often used as fillers to prepare two-dimensional composite papers and films or three-dimensional sponges and aerogels due to their excellent electrical conductivity,high aspect ratio and good mechanical flexibility.Cellulose nanofibers(CNFs)are abundant,low cost,biodegradable and have high crystallinity,excellent mechanical properties,and good biocompatibility.At the same time,CNFs with abundant active groups can bond with different conductive fillers,and then construct composite materials with enhanced structure through self-assembly.Therefore,using cellulose nanofibers and Ag NWs as substrates and fillers,it is expected to develop ultra-thin,flexi-ble and high mechanical properties electromagnetic shielding materials.In this study,using cellulose nanofibers(CNFs)as matrix,silver nanowires(Ag NWs)and graphene oxide(GO)as conductive fillers,the ultra-thin and flexible electromagnetic shielding composite paper with gradient structure(with a thickness of 34 µm)was constructed by an alternate vacuum filtration of CNFs and Ag NWs/GO mixtures with different proportions.The wet-tability,mechanical properties and electromagnetic shielding properties of the composite film were studied,and the in-fluence of the microstructure and composition of the composite paper on its wettability,mechanical properties and electromagnetic shielding properties were investigated.SEM results showed that the composite paper had a layered structure.The electrical conductivity test results showed that the conductivity of the three conductive layers varied in gradient.The results of the contact angle test showed that the contact angle of the composite paper was 115° after the formation of the multi-layer gradient structure,showing a certain hydrophobicity.The examination results obtained u-sing the universal mechanical testing machine showed that the composite paper with the gradient structure had a high stress and strain of 26.7 MPa and 2.16％,respectively,which was a certain increase compared with the mixed non-stratified composite paper.The test results of vector network analyzer showed that the electromagnetic shielding effi-ciency of the composite paper with gradient structure was 24 dB at 8.2 GHz,which was higher than that of the com-posite paper with hybrid non-gradient structure(19 dB),and the absorption loss was the main component.Thus,it can be concluded that the mechanical properties and electromagnetic shielding properties of composite paper can be significantly improved by constructing gradient structure.
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