Youna Kim1,Jinkee Hong1
Yonsei University1
Every year, exposure to volatile organic compounds (VOCs) causes fatal accidents including dyspnea and explosions. Personal protection equipment (PPE), such as VOCs sensors to monitor indoor air quality and masks to prevent inhalation of VOCs, is needed to prevent VOC exposure. However, single-functional PPE leads to inconvenience for workers as they must wear multiple pieces of PPE. Therefore, PPE must have the versatility to check not only air quality but also the health condition of workers.<br/>PPE combined with wearable electronics could provide multifunctionality with human health monitoring including strain and motion signals and VOCs detection. The electric materials for wearable electronics should be lightweight, flexible, and stretchable. Hydrogels are attracting attention in wearable electronics because of their flexibility, stretchability, and conductivity. However, it has weak mechanical strength and suffered the deterioration of conductivity and shape shrinkage due to moisture evaporation. Furthermore, few studies have controlled the mechanical and electrical properties of hydrogels due to VOCs exposure except for color changes. In order for VOCs-responsive hydrogels to exhibit various VOC-sensing performances, like actuation and electrical changes, an understanding of polymer behavior caused by VOCs must be investigated.<br/>In this study, we designed a VOC-responsive polymer network (VRN), a wearable electronics that can change its mechanical and electrical properties through VOC reaction. Through a solvation effect by different chemical affinity, the inter/intramolecular interaction and arrangement between polymer chains could be controlled. Based on the solvation effect, we considered (1) the control of polymer chain mobility and hydrogen bonding within VRN and (2) the chemical affinity between the VRN and VOCs.<br/>To control the VRN network, VRN is composed of polyvinyl alcohol (PVA) as hydrophilic semicrystalline and deep eutectic solvents (DES) as ionic liquids. DES is used as a processing and conductive additive to increase the entangled polymer chains and inhibit hydrogen bonding between polymer chains. Accordingly, VRN shows ionic conductivity and stretchability, which can be used for strain-responsive electrodes.<br/>After VOCs exposure, the increased hydrogen bonding and chain relaxation energies affected not only mechanical properties but also the electrical resistance of VRN. A relative resistance change (ΔR/R<sub>0</sub>) of VRN is increased by 50% when VRN is exposed to VOCs vapor. The peak voltage based on the triboelectric energy generator (TENG) system decreased by 30% due to VOCs exposure. VRN can be applied to PPE in various forms such as fiber and spray coating.<br/>In addition, we studied the VOCs responsive mechanism of polymer chains using rheological and Raman analysis. We expect VRN to propose VOCs-responsive mechanisms and technologies needed to move towards advanced PPE.