Ultralight, Flexible, and Biomimetic Nanocellulose/Silver Nanowire Aerogels for Electromagnetic Interference Shielding

Abstract

Ultralight and highly flexible biopolymer aerogels, composed of biomimetic cellular microstructures formed from cellulose nanofibers and silver nanowires, are assembled via a convenient and facile freeze-casting method. The lamellar, honeycomb-like, and random porous scaffolds are successfully achieved by adjusting freezing approaches to modulate the relationships between microstructures and macroscopic mechanical and electromagnetic interference (EMI) shielding performances. Combining the shielding transformation arising from in situ compression and the controlled content of building units, the optimized lamellar porous biopolymer aerogels can show a very high EMI shielding effectiveness (SE), which exceeds 70 or 40 dB in the Xband while the density is merely 6.2 or 1.7 mg/cm 3 , respectively. The corresponding normalized surface specific SE (defined as the SE divided by the material density and thickness) is up to 178235 dB•cm 2 /g, far surpassing that of the so-far reported shielding materials. Antibacterial properties and hydrophobicity are also demonstrated extending the versatility and application potential of the biopolymer hybrid aerogels.

Recent Progress on Nanocellulose Aerogels: Preparation, Modification, Composite Fabrication, Applications

“…Using this simple and flexible directional freeze drying technique, the selective adjustment of the aerogel structure can be realized by employing an appropriate cold source (liquid nitrogen at −196 °C or milder cold ethanol with adjustable temperatures) and temperature gradients, [ 48 ] and has been promoted in numerous fields of nanocellulose aerogel applications, including selective absorption, [ 51 ] gas capture, [ 52 ] solar steam generation, [ 12d ] EMI shielding, [ 53 ] energy storage, [ 52 ] strain sensor, [ 54 ] and others. [ 31,55 ]…”

“…Therefore, researchers have introduced these metal materials as functional fillers into nanocellulose aerogels to enrich their uses. [ 18d,44a,53b,80 ]…”

“…For mobile charge carriers to interact with the incoming EM field and for the porous structure to promote the multiple reflections, adsorption of EM waves plays an important role. Compared with other 1D or 2D conducting composites, nanocellulose composite aerogels exhibited promising properties for EMI shielding by introducing novel conductive fillers (e.g., silver nanowires (AgNWs), [ 53a ] MXene [ 99,180 ] ), as they can combine advantages of nanocellulose, conductive fillers, and aerogels including i) biocompatibility, biodegradability, and chemical stability, ii) excellent electrical conductivity, and iii) ultralow density, large open pores, and ultrahigh SSA.…”

“…assembled 1D AgNWs with a higher aspect ratio and electrical conductivity into CNF dispersions, forming ultralight and highly flexible CNF/AgNW composite aerogels via unidirectional freeze drying ( Figure a). [ 53a ] The lamellar, honeycomb‐like porous structures, and effective conductive networks provided by the AgNWs, and strong hydrogen bond interactions between CNFs and polyvinylpyrrolidone adsorbed on the AgNW surfaces endowed aerogels with a markedly high EMI shielding effectiveness (SE) of >70 dB (Figure 23b). Fei et al.…”

Ice-Templated Cellulose Nanofiber Filaments as a Reinforcement Material in Epoxy Composites

“…Ice-templating is a method that can be used to turn a nanocellulose water suspension into a porous honeycomb-like structure [18][19][20]. The resulting aerogels are composed of aligned pores that run through the material in the direction of the ice crystal growth and can be used as preforms for composite materials by filling the structure with a polymer [21][22][23].…”