Nanoarchitectonics of RGO‐Wrapped CNF/GO Aerogels with Controlled Pore Structures by PVA‐Assisted Freeze‐Casting Approach for Efficient Sound and Microwave Absorption**

Abstract

Acoustic absorption materials play an important role in eliminating the negative effects of noise. Herein, a polyvinyl alcohol (PVA)‐assisted freeze‐casting was developed for controllably fabricating reduced graphene oxide wrapped carbon nanofiber (RGO@CNF)/graphene oxide composite aerogel. During the freeze‐casting, PVA was used as an icing inhibitor to control the size of ice crystals. While the concentration of PVA increased from 0 to 15 mg ⋅ ml−1, the average pore size of the aerogel was reduced from 154 to 45 μm. Due to the modulation of the pore size and composition, the propagation path and friction loss for sound were optimized, especially at low frequency. For instance, the normalized sound absorption coefficient of RGO@CNF/GO‐10 achieves 0.79 (250–6300 Hz). The sample also exhibits a desirable microwave absorbing property whose maximum reflection loss is −47.3 dB (9.44 GHz, d=3.0 mm). Prospectively, this synthetic strategy can be extended to develop other forms of elastic aerogel with a controlled pore size.

High-Performance Microwave Absorption Materials: Theory, Fabrication, and Functionalization

“…According to transmission line theory, the input impedance ( Z in ) of the material can be expressed as Z in = Z 0 μ r ε r tanh true( normalj 2 π italicf italicd italicc μ normalr ε normalr true) where Z 0 is the free-space impedance of material, μ r and ε r are the complex permeability and the complex permittivity, respectively, d is the thickness of the material, c is the speed of light, and f is the frequency of microwaves …”

“…where Z 0 is the free-space impedance of material, μ r and ε r are the complex permeability and the complex permittivity, respectively, d is the thickness of the material, c is the speed of light, and f is the frequency of microwaves. 55 The wave absorption properties of material can be assessed by refection loss (RL) calculated by the formula 5: 56…”