A facile route to mechanically robust graphene oxide fibers

Abstract

Excellent mechanical, electrical, and thermal properties of graphene have been achieved at the macroscale by assembling individual graphene or graphene oxide (GO) particles. Wet-spinning is an efficient and well-established process that can provide GO assemblies in fiber form. The coagulation bath in the wet-spinning process has rarely been considered for the design of mechanically robust GO fibers (GOFs). In this study, locating the amidation reaction in the coagulation bath yielded mechanically improved GOFs. The imides 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide and N-hydroxysuccinimide were used to form covalent amide bonds between GO flakes and chitosan, thereby reinforcing the GOFs. Evidence and effects of the amidation reaction were systematically examined. The tensile strength and breaking strain of the GOFs improved by 41.6% and 75.2%, respectively, and the toughness almost doubled because of the optimized crosslinking reaction. Our work demonstrated that using a coagulation bath is a facile way to enhance the mechanical properties of GOFs.

Fig. 1. Cross-sectional and surface field-emission scanning electron microscopy images of graphene oxide fibers (GOFs) and chemically crosslinked GOFs (C-GOFs). (a and b) GOFs, (c and d) C-GOF1, (e and f) C-GOF2, (g and h) C-GOF3, (i and j) C-GOF4, and (k and l) C-GOF5. Marked areas were used for the effective diameter calculation.

Fig. 2. Schematic diagrams describing (a) amide bond formation between graphene oxide (GO) flakes and chitosan molecules via the 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC)/N-hydroxysuccinimide (NHS) activation mechanism and (b) wet-spinning for manufacturing continuous GO fibers using the amidation reaction.

Fig. 3. Characterization of the amidation reaction. (a) Fourier transform-infrared spectra and (b) wide-scan X-ray photoelectron spectra of GOF and C-GOFs. Deconvoluted high-resolution N1s signal for (c) GOF, (d) C-GOF1, (e) C-GOF2, (f) C-GOF3, (g) C-GOF4, and (h) C-GOF5.

Fig. 4. Thermal decomposition behaviors of raw materials and GOFs. (a) Full temperature range and (b) near 500 degrees of thermogravimetric curves. (c) Differential scanning calorimetry curves.

Fig. 5. Diameter change of GOFs soaked in distilled water with increasing time during the swelling test. (a) Long and (b) short soaking times.

Fig. 6. Mechanical properties of the GOFs. (a) Typical stress–strain curves, (b) Young's modulus, (c) tensile strength, (d) elongation at break, and (e) toughness.

Fig. 7. Low and high magnification field-emission scanning electron microscopy images of fractured cross-sectional surfaces of GOFs and C-GOFs. (a and b) GOFs, (c and d) C-GOF1, (e and f) C-GOF2, (g and h) C-GOF3, (i and j) C-GOF4, and (k and l) C-GOF5.