Smart yarns are set to revolutionize the textile industry by combining traditional fiber technology with cutting-edge materials capable of electrical conductivity and adaptability. These advanced fibers can communicate and interact with their environment while maintaining their integrity under mechanical stress. The development of innovative materials, such as liquid metal (LM), has paved the way for the creation of yarns that offer high elasticity while effectively conducting electricity, crucial for the wearable technology sector.
The Promise of Smart Yarns
For centuries, fiber materials have facilitated human progress by offering essential functions in clothing and textiles. Today, the focus has shifted to smart yarns that can autonomously adapt to environmental changes. The infusion of state-of-the-art materials, including conductive fibers made from carbon nanotubes, graphene, and metal coatings, is at the heart of these innovations. Yet, achieving the required flexibility and conductivity for wearable applications has proven challenging due to the high modulus of many conductive fibers.
Tackling Challenges with Liquid Metal
Liquid metal offers a promising solution to the challenges facing conductive fibers. Known for its excellent adaptability and fluidity, liquid metal can adjust its volume in response to compressive forces, ensuring that conductive pathways remain intact even when the fiber is stretched or deformed. This adaptability is crucial, as the goal is to develop fibers capable of reliably transmitting electrical signals during various mechanical stressors.
To address issues such as dewetting, which can result in conductivity loss, researchers have proposed an innovative adhesion-channel strategy. This method integrates silver nanoparticles (Ag NPs) onto a yarn substrate, with the capillary wicking effect of microfibers enabling the effective infiltration of liquid metal while maintaining strong linkages and interfacial adhesion.
Innovative Fabrication Techniques
The creation of this advanced yarn — known as SBS/LM/Ag-SBS (SLMAS) yarn — involves a multi-step process that optimizes conductivity and elasticity. The fabrication technique includes the following key stages:
- Microfiber Construction: Poly(styrene-block-butadiene-block-styrene) (SBS) microfibers are electrospun onto spandex yarn to create a base yarn featuring a three-dimensional microchannel structure.
- Metalization: The microfibers are coated with a layer of silver, enhancing their wettability with liquid metal compared to other metals like copper or nickel.
- Liquid Metal Adsorption: The yarn is immersed in a liquid metal bath, allowing for effective adsorption which produces high conductivity.
- Encapsulation: A layer of waterproof electrospun microfibers is applied to protect and encapsulate the conductive layers, yielding the final SLMAS yarn.
The SLMAS yarn’s fabrication not only enhances its electrical performance but also ensures the robust adhesion of liquid metal through multiscale interlocking.
Performance Characteristics
The electromechanical properties of SLMAS yarns are remarkable. The addition of liquid metal significantly reduces electrical resistance from 1.600 Ω/cm (with no liquid metal) to just 0.082 Ω/cm when saturated. Moreover, with optimal liquid metal loading, the yarn exhibits minimal resistance changes even under strains up to 600%, demonstrating an impressive resistance change of only 0.703.
The yarns also maintain structural integrity under various mechanical stresses, including bending, twisting, and washing. In a demonstration, the yarn successfully powered an LED display while being stretched to a length of 550%, showcasing its practical application in smart textiles.
Joule Heating Capabilities
The high electrical conductivity of the SLMAS yarns enables them to serve as effective low-voltage heaters. Temperature measurements indicate that yarns can reach up to 122.7°C when the liquid metal content is maximized at 6.88 mg/cm and supplied with a voltage of 1.0V. Importantly, the heating performance remains relatively stable even under stretching, with negligible temperature change reflecting the yarn’s reliability in thermal applications.
Electro-Thermochromic Applications
In another application, researchers have created electro-thermochromic yarns by incorporating thermochromic microcapsules into the outer layer. Upon applying a voltage, the yarns display visible color changes, demonstrating potential use in advanced, responsive textiles that change appearance based on environmental conditions.
Stability and Long-term Performance
SLMAS yarns exhibit exceptional durability and resiliency. They maintain consistent electrical properties even after extensive cyclic loading, demonstrating their potential viability for long-term applications in wearable technology. These findings are underlined by testing that confirms an impressive operational lifespan, with minimal resistance changes noted after prolonged use.
Conclusion
The development of SLMAS yarns exemplifies a significant leap forward in textile technology, integrating advanced materials to create smart textiles capable of maintaining electrical conductivity and structural integrity under mechanical deformation. This innovation holds promise not only for wearable technologies but also for a variety of applications across electronics, sensing, and heating. With their compelling properties, smart yarns are poised to redefine the future of textiles, offering functional solutions that seamlessly blend with everyday life.