Improvement of electromagnetic interference properties of 3D few-layer graphene composite by means of freeze-drying

In this paper, we present a facile, green, and scalable approach for preparing high-quality few-layer graphene (FLG) nanoplatelets through a jet cavitation process. The electromagnetic interference (EMI) performance of FLG of three different lateral sizes is investigated. The midsized FLG (M-FLG) exhibits the best EMI performance. The jet-exfoliation technology used herein preserves the structure of FLG with few structural defects. The I-D/I-G ratio of M-FLG is as low as 0.092. Furthermore, we introduce 20 wt% M-FLG into paraffin wax to obtain a bulk material for conducting shielding measurements. The shielding effectiveness (SE) in the X-band is 19.28 dB, which exceeds that of unexfoliated graphite. Finally, we use freeze-drying technology to inhibit stacking of the graphene suspension during drying. The SE of the freeze-dried M-FLG (M-FLG-fd) increased considerably to 39 dB. The results indicate that jet cavitation combined with freeze-drying substantially improved the dielectric properties and absorption capabilities of FLG.