Terahertz Birefringent Biomimetic Aerogels Based on Cellulose Nanofibers and Conductive Nanomaterials

Abstract

Biomimetic, lamellar, and highly porous transition-metal carbide (MXene) embedded cellulose nanofiber (CNF) aerogels are assembled by a facile bidirectional freeze-drying approach. The biopolymer aerogels have large-scale, parallel-oriented micrometer-sized pores and show excellent mechanical strength and flexibility, tunable electrical properties, and low densities (2.7–20 mg/cm3). The CNF, MXene, and lamellar pores are efficiently utilized to endow the aerogels with exceptionally high birefringence in the terahertz (THz) regime. Birefringence values as high as 0.09–0.27 at 0.4 THz are achieved, which is comparable to most commercial THz birefringent materials such as liquid crystals, which suffer from fast disintegration, high cost, and complicated preparation processes. Empirical modeling for different MXene contents and an experimental comparison with silver nanowire or carbon nanotube embedded CNF aerogels suggest that the intrinsic conductivity and content of embedded nanomaterials, the aerogel porosity, and the lamellar cell walls can affect the optical properties such as the THz birefringence and absorption. The determination of optical anisotropy in the biopolymer aerogels lays a foundation for further exploration of ultralight, freestanding, and low-cost biomimetic porous architecture-based THz devices.

Porous and Ultra-Flexible Crosslinked MXene/Polyimide Composites for Multifunctional Electromagnetic Interference Shielding

“…AFM image is further provided, and the thickness of ~ 1.7 nm can be identified for a single MXene flake (Fig. 1 d); this is consistent with the previous reports [ 26 , 27 , 55 ]. The pure PI foams showed micrometer-sized pores and smooth pore cell surfaces (Fig.…”

“…First, a stable Ti 3 C 2 T x MXene (T represents the surface hydrophilic functional groups (-OH, -O, and -F)) in an aqueous dispersion was prepared by etching and delamination of the precursor Ti 3 AlC 2 MAX with a compact rocklike microstructure (Figs. 1 a and S1a) [ 26 , 27 ]. After etching of Al layers of MAX precursor [ 26 , 54 ], multilayer Ti 3 C 2 T x (m-Ti 3 C 2 T x ) was obtained (Fig.…”

“…Ti 3 AlC 2 MAX with a compact rocklike microstructure (Figs. 1a and S1a) [26,27]. After etching of Al layers of MAX precursor [26,54], multilayer Ti 3 C 2 T x (m-Ti 3 C 2 T x ) was obtained (Fig.…”

“…However, the interactions formed among MXene flakes are generally very weak, which is against the formation of robust pure MXene porous structures [20,22,25], and consequently hinder its practical applications. Polymers acting as efficient 'binder phase' are most widely employed to improve the mechanical strength and flexibility of MXenebased macrostructures [26,27]. The poly (vinyl alcohol) (PVA) [28], sodium alginate (SA) [22], aramid fiber (ANF) [29,30], and cellulose nanofiber (CNF) [26,[31][32][33][34] have been reported to achieve mechanical strong and flexible MXene-based composites.…”

Effects of different amounts of cellulase on the microstructure and soluble substances of cotton stalk bark

“…As one of the three major components of plant biomass, cellulose has attracted much attention. Cellulose can be used to make paper, paperbased materials, hydrogels, and aerogel [23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38][39]. Besides, cellulose and its derivatives can be applied in the field of electrical materials [40][41][42][43][44][45].…”