Stretchable, transparent, self-adhesive, anti-freezing and ionic conductive nanocomposite hydrogels for flexible strain sensors

Conductive hydrogels have attracted considerable attentions due to their great potential in the field of flexible strain sensors. However, the low stretchability, poor adhesiveness as well as the lack of freezing-resistant capacity of conventional conductive hydrogels greatly limited their practical applications. Herein, a stretchable, transparent, self-adhesive and anti-freezing conductive nanocomposite hydrogel (PAHS gel) was fabricated via a one-step in situ free-radical polymerization of sulfobetaine methacrylate (SBMA), acrylic acid (AA) and 2-hydroxyethyl methacrylate (HEMA) in the presence of alumina nanoparticles (Al2O3 NPs) and lithium chloride (LiCl) as the inorganic cross-linkers and conductive substance, respectively. The obtained PAHS gels displayed high transparency (higher than 85 % at 550 nm), excellent stretchability (up to 800 %) and good ionic conductivity (2.25 S/m) and could keep flexible and conductive at the temperature at −18 ℃. Furthermore, the various types of functional groups on the polymer chains endow the PAHS gels with strong self-adhesiveness to different substrates such as glass, rubber, skin, etc. In addition, the PAHS gels also revealed superior strain sensitivity (GF = 2.69) in the strain of 0 ∼ 100 %, which can be assembled into wearable strain sensors to monitor various human activity. Based on these combined merits, it is believed that this newly developed conductive nanocomposite hydrogel would have prospective applications in the field of wearable strain sensors and other flexible electronics.