Fatigue-Free Electrodes Enabled Joule Heating Device for Wearable Thermotherapy

Abstract

Wearable Joule heating devices have received tremendous attention from researchers due to their applications in personal thermal management systems, like thermal management cloth, and healthcare application, such as wearable thermotherapy. Permeability, stretchability, dynamic stability, and conductivity are essential factors for electrothermal heating devices. Wearable devices usually work under cyclic loading of low stain, so fatigue, mechanical failure induced by cyclic loading at low strain level, is a common disease for metal electrodes. Fatigue-free materials are of great importance to ensure robustness for long-term application. Stretchable electrodes, such as noble metal nano mesh, conductive fillers-based elastomer and metal nanowires have been used to fabricate wearable heater. Liquid metal (LM) has also attracted lots of attention due to its high conductivity and fluidity at room temperature. Such fluidity not only makes LM attractive materials for flexible devices, but also render LM fatigue-free attribute. Many manufacturing methods, such as direct ink writing, screen printing and spray coating have been applied to fabricate LM based electrodes for flexible devices. Recently, electrospun technique have also been applied to fabricate LM particles doped polymer fibers, but LM based conductive fiber electrodes have not yet been fabricated using electrospun process. Here, a LM particles embedded fibers network electrode is fabricated using electrospun method, followed by wrapping a polymer layer on the fiber surface. The LM particles embedded in the electrospun fibers form interconnected network, which exhibits excellent electrical conductivity, high mechanical stretchability, and good fatigue performance. Such network electrode could be directly used as a Joule heater, which is permeable, stretchable and fatigue-free. High conductivity of the electrodes ensures low driving voltage for this electrothermal heating devices. High stretchability of the electrode ensures good Joule heating performance at high strain level. In addition, the uniform fibers size could induce large-scale uniform heating. The LM fiber electrodes could be cut into various patterns to fit curvilinear surface of human skin. Also, the ultrathin and compliant nature of the LM fiber electrode enable seamless attachment with human skin, which could ensure high thermal transfer efficiency. The combination of good electrical and mechanical performances of the LM fiber-based Joule heater enable long-term wearable thermotherapy.