Unlimited recyclable wearable sensors based on a homogeneous ionic liquid and polyvinyl alcohol network

Abstract

Smart wearable electronics are now of great significance in the fields of biomedical applications and environmental sensors. The development of new devices will be a continuing pivotal hotspot for human beings in future. However, contamination caused by large quantities of traditional electronic waste has already done serious damage to the reputation, especially the unignorable and irreversible environmental pollution caused by the leakage of heavy metal ions and plastic microparticles. To address the issues mentioned above, we design recyclable, flexible and stretchable homogeneous wearable sensors, which are hydrogen bonding crosslinked polyvinyl alcohol (PVA) conductive films, via applying ion-conductive 1-hexyl-3-methylimidazolium bromide ([HMIM]⁺Br⁻) ionic liquids, into a PVA polymer network by the freeze-thawing method. The application of [HMIM]⁺Br⁻ (Br-IL) can guarantee stable conductivity with no effect on the recyclability of the whole device. What's more, Br-IL also endows the PVA film with tuneable properties, such as enhancing the flexibility and stretchability of films which is a challenge for polymer-based electronics. Not only that, Br-IL also creates a bi-continuous ion conductive phase structure in the polymer network, which could be called a “swimming lane effect”. Experiments successfully prove that the PVA/Br-IL ion-conductive films can be used for strain/temperature/humidity sensing applications with perfect recyclability and reusability.