Multi-Purpose Kevlar Liquid Crystal Airgel Fibers
Airgel fibers outperform natural and synthetic fibers in thermal insulation.
Study: Nanoscale Kevlar Liquid Crystal Airgel Fibers. Image Credit: Composite_Carbonman/Shutterstock.com
In a paper published in the journal ACS Nano, nano-sized Kevlar liquid crystal (LC) airgel fibers with varying degrees of building block arrangement were created from Kevlar nanofibers. A sequential approach of LC spinning, dynamic sol-gel process, cryodesiccation and cold plasma hydrophobization was followed.
Thermal insulation using airgel fibers
Thermal insulation in extreme conditions is essential for human survival. The market for highly efficient thermal insulation fibers is still expanding. For thermal insulation, the fibers must be very porous, with a very low density.
Airgel fibers have been hailed as the future of high performance thermal protection for humans. These fibers have the advantages of very low densities, very high porosities and large specific surfaces. Airgel fibers have shown major advantages over synthetic and natural fibers for thermal protection.
Significant efforts have been made in recent years to produce different airgel fibers.
Through reaction spinning, silica airgel fibers with good thermal insulation and broad temperature stability have already been created, with enormous promise for wearable applications.
Polyimide airgel fibers, with low thermal conductivity and a wide operating temperature range, were created using a confined sol-gel transition technique. These airgel fibers can be used as thermal insulation components in harsh conditions, including fire resistance and cold protection.
Several conductive airgel fibers based on metallic nanoparticles or graphene sheets have been developed over the years, with applications in electronics, energy management and joule heating.
Manufacture of airgel fibers
Airgel fibers differ from monolithic aerogels not only in shape but also in manufacturing techniques.
Aerogels are traditionally made using a sol-gel transition technique and either freeze-drying or a supercritical drying procedure.
The static sol-gel transition procedure for generating airgel monoliths can be used to produce any airgel, including metallic aerogels. To produce airgel fibers, wet spinning or reaction spinning is often used, resulting in a dynamic sol-gel transition mechanism.
This dynamic technique imposes limitations on the sizes of the airgel building blocks. The building blocks at the molecular level are far too small to perform the sol-gel procedure after being centrifuged in the coagulation bath. Yet, the micron-sized building blocks are too large to achieve the desired airgel fibers having a large specific surface area.
What did the researchers do?
Nanoscale structures like nanofibers, nanosheets and nanoparticles are the only suitable building blocks to produce airgel fibers. The team designed and fabricated nanoscale Kevlar LC airgel fibers in this study.
The inherent advantages of nanoscale Kevlar have allowed it to be used as a building block to construct airgel fibers with well-directed patterns.
The nanoscale Kevlar LC was subjected to liquid crystal wet spinning, dynamic sol-gel transition, freeze drying and cold plasma treatment to create airgel fibers with arranged and controlled microstructures.
Nano-scale Kevlar LC airgel fibers provided significant thermal insulation. After being soaked in a suitable solvent, Kevlar LC airgel fibers with varying degrees of building block arrangements transformed into corresponding gel fibers.
The nanoscale Kevlar LC airgel fiber showed dual functionality. These functions included thermal insulation as well as information encryption.
Nanoscale Kevlar LC airgel fibers with an adjustable building block arrangement were grown using matching LC spinning in a coagulating bath of proton-donating solvent.
Nanoscale Kevlar LC airgel fibers with varying building block orientations exhibited distinct luminosity under polarized light and were created by varying the amount of Kevlar nanofibers and draw ratio in the transition procedure dynamic sol-gel.
The associated nanoscale Kevlar LC airgel fibers have shown extraordinarily high mechanical strength, excellent thermal insulation and super hydrophobic characteristics.
By absorbing ethyl alcohol and drying at atmospheric pressure, the fabric woven from these nanoscale Kevlar LC airgel fibers can be cyclically exchanged between airgel-gel.
Interlacing or stitching using the produced nanoscale Kevlar LC airgel fibers with different building block orientations allowed the team to obtain a digital fabric containing encrypted data such as barcodes.
The developed structure demonstrated exceptional information security. Encrypted data could only be decrypted if the digital cloth was immersed in ethyl alcohol and then viewed under polarized light.
This study highlighted the potential of nanoscale Kevlar LC airgel fibers for applications in thermal insulation, data encryption, and on-demand decoding.
Liu, Z., Lyu, J., Ding, Y., Bao, Y., Sheng, Z., Shi, N. & Zhang, X. (2022). Nanoscale Kevlar liquid crystal airgel fibers. ACS Nano. Available at: https://pubs.acs.org/doi/10.1021/acsnano.2c06591