Bending Stiffness-Directed Fabricating of Kevlar Aerogel-Confined Organic Phase-Change Fibers

Significance 

Smart and functional fibers are the basic building blocks of fabrics. Besides, they find applications in other fields such as wearable electronics and solar cells. Although much have been done on the functionality of smart fibers, their wearing comfort has been given limited attention as most smart fiber suffers from negative wearing experience. Generally, the wearing comfort of smart fibers is related to several parameters, including moisture, temperature, bending stiffness and contact, which can be modified to achieve the desired temperature regulation capabilities and many other applications.

Smart fibers with effective thermal comfort management capabilities are desirable for more comfortable living. Phase change fibers fabricated by combining phase change materials (PCMs) and advanced fiber manufacturing techniques are promising candidates for effective temperature control and regulation. An increase in the ambient temperature changes the PCM from solid to liquid to absorb and store heat in the fiber. In contrast, the PCM releases the stored heat by changing from liquid to solid when the ambient temperature decreases. Thus, phase change fibers enable intelligent thermal control and regulation. Although many phase-change fibers have been reported, their phase change enthalpies are significantly low, leading to poor temperature-regulation performance.

Nanoconfinement strategies can address the inherent leakage problems and improve enthalpy values of phase-change fibers. Aerogel fibers rich in mesopores, particularly Kevlar aerogel fiber (KAF), are suitable candidates for nanoconfinement of PCM to fabricate phase change fibers owing to their low density and large specific surface area. Although KAF exhibits superior mechanical strength than other aerogel fibers, its hydrophilic nature could make it shrink upon contact with water of moisture surface, resulting in the possible collapse of the aerogel structure. Thus, conducting hydrophobic functionalization in KAF is of great significance in their application as porous media for fabricating smart phase change fibers.

On this account, Ms. Yaqian Bao, Dr. Jing Lyu, Mr. Zengwei Liu and Dr. Yi Ding and led by Professor Xuetong Zhang from the Suzhou Institute of Nano-tech and Nano-bionics, Chinese Academy of Sciences fabricated the smart hydrophobic Kevlar aerogel-confined paraffin wax fiber ([email protected]) via the newly proposed bending stiffness-directed strategy. Specifically, the fiber was fabricated by employing paraffin as the functional guest and hydrophobic-KAFs as the porous host. The hydrophobic-KAFs were obtained via a two-step KNF functionalization process in a special coagulation bath comprising n-bromobutane and ethanol mixture. The main objective was to fabricate smart phase change fibers with controllable diameters and various bending stiffness desirable for different applications. The work is currently published in the research journal, ACS Nano.

The authors showed that the as-prepared [email protected] exhibited excellent thermal cyclic stability at constant enthalpy values even after 100 cycles, good mechanical properties of 30% in tensile strain and 30 MPa in tensile strength and high latent heat value (135.1 – 172 J/g) attributed to high filling ratio of up to 90.2%. The superiorities of the [email protected] was attributed to large specific surface area (326 – 353 m2/g) of the as-prepared hydrophobic aerogel fiber provided the required mesoporous matrix for confining paraffin. [email protected] with low bending stiffness (fiber diameter < 91.8µm) in both molten and solid states of the PCM exhibited high flexibility coupled with high washable performance and thermal management capability suitable for fabricating smart temperature-regulating fabrics. In contrast, those with high bending stiffness above the critical value can be used as shape-memory materials due to the transition between flexibility and rigidity.

In summary, the research team successfully designed the fabrication of [email protected] with different stiffness using the bending stuffiness-directed method. This approach enabled effective control of the fiber diameter, allowing the fabrication of [email protected] with superior properties. The proposed concept was successfully validated by designing a dynamic gripper based on the [email protected] with a fiber diameter of 400 µm. The gripper effectively transported items by gripping and releasing them under low and high temperatures, respectively. In a statement to Advances in Engineering, Professor Xuetong Zhang, the corresponding author who is also affiliated with University College London said that their findings advance the diverse application of phase-change composites in smart fabrics and intelligent control systems.

Reference

Bao, Y., Lyu, J., Liu, Z., Ding, Y., & Zhang, X. (2021). Bending Stiffness-Directed Fabricating of Kevlar Aerogel-Confined Organic Phase-Change FibersACS Nano, 15(9), 15180-15190.

Go To ACS Nano

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