Xiaojing Zhang,Bo Liu,Wenbo Feng,Wangchong Wei,Weiwei Shen,Shaoming Fang,Kaiqi Fan
Conductive composite hydrogels are attracting much attention as artificial skin-like materials, with great potential for applications in wearable electronics, flexible printable electronics, and tissue engineering scaffolds. However, the design of conductive hydrogels possessing multifunctional properties such as excellent mechanical properties , self-healing, high conductivity, low swelling ratio (SR), and high strain sensitivity remains a challenge. Here, we designed and synthesized a polyhedral oligomeric silsesquioxane (POSS)-based composite hydrogel (OCAPS/PAA–Na/PAM) via the copolymerization of acrylamide and an ionic supramolecular monomer consisting of a cationic octa(3–chloroammoniumpropyl) silsesquioxane (OCAPS) core surrounded by sodium acrylate to achieve a combination of high stretchability, low SR, self-healing, high conductivity, biocompatibility, and strain sensing properties. The introduction of OCAPS as a physical crosslinking agent enhanced the toughness and compression properties of the hydrogel. The SR of the OCAPS/PAA–Na/PAM hydrogel was greatly suppressed, with a much lower value (SR: 200 %) than that of the hydrogel without POSS (SR: ~22,000 %). The elongation at break and fracture energy reached 4396 % and 3.7 kJ·m −2 , respectively. OCAPS/PAA–Na/PAM hydrogels also had good self-healing properties due to the sufficient electrostatic interactions and hydrogen bonding between OCAPS and the polymer chains. Moreover, the supramolecular monomers provided abundant ion sites and in-situ generated NaCl , which imparted good electrical conductivity (0.678 mS·cm −1 ) and excellent strain sensitivity (gauge factor = 3.78) to the hydrogel. The OCAPS/PAA–Na/PAM hydrogel could detect electrical signal changes in large strain and small limb deformation and they showed good biological transmission sensitivity, which is expected to contribute to the fields of safety detection, gait detection, and wearable devices .
Conductive hydrogels can be utilized in the field of flexible supercapacitors due to their stretchable properties and high ionic conductivity. However, many of the conductive hydrogels lose their stretchability and conductivity at subzero temperatures. Herein, a novel Janus POSS-based hydrogel electrolyte that shows excellent flexibility and ionic conductivity at low temperatures is designed and prepared by the copolymerization of acrylamide and a water-soluble Janus-type polyhedral oligomeric silsesquioxane (AS-POSS) containing sodium sulfonate groups and double bonding groups. The sodium sulfonate groups of AS-POSS and LiCl endow the hydrogel electrolyte with excellent anti-freezing ability. Simultaneously, the double bonding groups of AS-POSS enable a successful POSS crosslinking in the polymer network, resulting in a highly stretchable hydrogel electrolyte (1445%) with high ionic conductivity (0.067 S cm −1 ) at −20°C. Thereafter, the all-in-one flexible supercapacitor is prepared by in-situ polymerization of aniline. Based on the exceptional anti-freezing properties of the Janus POSS-based hydrogel electrolyte, the all-in-one supercapacitor exhibits stable electrochemical performance (>90% capacitance retained under deformation at −20°C) and excellent cycling stability (only 19.7% capacitance decay over 2000 charge/discharge cycles at −20°C) at low temperatures. The Janus POSS-based hydrogel electrolyte is expected to be a promising gel electrolyte for an all-in-one supercapacitor that resists freezing.
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