Multi-functional integrated organohydrogel fibers for wearable electronics

Abstract

Nowadays, the development of wearable electronics towards miniaturization and high integration with textiles and clothing for varied applications such as healthcare, entertainment, sports, and communication systems. Compared with traditional planar wearable electronics, fiber-based electronics have miniature, lightweight, flexible and wearable advantages, enabling them to fit conformally to the irregular surface of the human body. Especially, stretchable conductive fibers have become the essential components in wearable electronics, which can be widely used as interconnectors and electrodes with strain-independent conductance or multiple sensors with strain-dependent conducting performances. Considering the unexpected damages and harsh environments in the actual practical scenarios, the development of multi-functional integrated fibers with the metrics of stretchability, self-healing ability, conductivity, and multi-environmental tolerance are of great significance, enhancing the durability and stability of fibers. Among them, organohydrogel fiber is one of the ideal substrates for preparing conductive fibers because of its potentially excellent stretchability, multi-environmental tolerance, and self-healing feasibility by deliberately designing components. However, challenges remain in balancing mechanical properties, electrical performances, and self-healing abilities. Until now, the advent of multifunctional conductive fiber with stretchable and self-healable properties and adaptability to complex and harsh environments (such as cold, dry, or wet conditions) is still vacant. Moreover, another challenge lies in the absence of a high-throughput and cost-effective fabrication for producing long and continuous organohydrogel fibers to realize the multi-functional integration. To address these challenges, this thesis focused on developing the multi-functional integrated organohydrogel fibers through the delicate design of materials, structures, and processing technologies in facile manners. As a result, two types of conductive organohydrogel fibers, based on different conducting mechanisms and facile fabrications, are demonstrated. Firstly, glycerol/water binary solvent was prepared through a template method and in-situ photopolymerization of acrylic acid (AA) monomers in the binary solvent. The as-prepared poly(acrylic acid) (PAA) organohydrogel fibers exhibited highly stretchable, durable, and self-healing performances in cold and arid conditions, owing to the multiple hydrogen bonds between glycerol, water and PAA chains. Subsequently, highly conductive fibers were developed based on the PAA organohydrogel fibers. A simple dip-coating method was adopted to coat the AgNWs sheets onto the pre-stretched organohydrogel fibers to form a buckled and continuous conductive layer, then encapsulated by the PDMS. The macroscopically buckled structures and PDMS sheath rendered ultrahigh conductivity and excellent strain-insensitive resistance under large deformation, no matter in ambient, cold, arid, or underwater conditions. They were also integrated into wearable form by embroidery techniques as stable and durable interconnectors in the E-textiles. Then another conductive organohydrogel fibers were developed by a dynamic spinning method based on the fast polymerization of AA under UV irradiation and constant drawing of the pre-gels. The key factors for the continuous spinning were the proper photopolymerization time under UV irradiation and moderate mechanical properties to withstand the post drawing. As a proof of concept, a long organohydrogel fiber consisting of PAA and carboxymethyl cellulose (CMC) in the binary solvent of ethylene glycol (EG)/water crosslinked by Al3+-ligand coordination and hydrogen bonds was prepared by this method. The fiber exhibited competitive mechanical properties and high mechanical self-healing performance. Due to the transfer of ions inside the liquid phase, the fiber also exhibited moderate ionic conductivity and strain-sensitive conducting even under -20 ℃, enabling it to be a strain sensor in varied environments. Besides, a distinct humidity sensitivity was observed due to the hygroscopicity of EG and LiCl, indicating its potential as a multi-responsive sensor. In summary, this work explored the feasibility of preparing multi-functional integrated organohydrogel fibers through the materials and structure design, as well as a novel fabrication strategy. The template method and dip-coating method were utilized to design sandwiched-structural fibers with ultrahigh electron conductivity. And the novel dynamic spinning method realizes the scalable and one-step fabrication of ionically conductive organohydrogel fibers. And by deliberately designing the composition of precursor solution, both the as-prepared conductive fibers have excellent stretchability and self-healing ability under varied environments. In principle, these design concepts can be applied to other materials, which can introduce diverse functions in the conductive fibers and further impact the fields of wearable electronics.