Shear-Thickening Covalent Adaptive Networks for Bifunctional Impact-Protective and Post-Tunable Tactile Sensors

Abstract

Shear-thickening materials have been widely applied in fields related to smart impact protection due to their ability to absorb large amounts of energy during sudden shock. Shearthickening materials with multifunctional properties are expanding their applications in wearable electronics, where tactile sensors require interconnected networks. However, current bifunctional shear-thickening cross-linked polymer materials depend on supramolecular networks or slightly dynamic covalently cross-linked networks, which usually exhibit lower energy-absorption density than the highly dynamic covalently cross-linked networks. Herein, we employed boric ester-based covalent adaptive networks (CANs) to elucidate the shear-thickening property and the mechanism of energy dissipation during sudden shock. Guided by the enhanced energy-absorption capability of double networks and the requirements of the conductive networks for the wearable tactile sensors, tungsten powders (W) were incorporated into the boric ester polymer matrix to form a second network. The W networks make the materials stiffer, with a 13-fold increase in Young's modulus. Additionally, the energy-absorption capacity increased nearly 7 times. Finally, we applied these excellent energy-absorbing and conductive materials to bifunctional shock-protective and strain rate-dependent tactile sensors. Considering the self-healable and recyclable properties, we believe that these anti-impact and tactile sensing materials will be of great interest in wearable devices, smart impact-protective systems, post-tunable materials, etc.

Entropy-Driven Design of Highly Impact-Stiffening Supramolecular Polymer Networks with Salt-Bridge Hydrogen Bonds

“…This high energy-dissipating behavior of the polyTA/arginine SPN stems from its high loss moduli (G″ = 0.25∼16.7 MPa from 0.1 to 100 Hz, Figure 2d), which represents the energy dissipated as heat at a specified frequency. 51 Furthermore, to examine the impact-stiffening behavior of the polyTA/arginine SPN in the high-speed regime, a split-Hopkinson pressure bar (SHPB) system, comprising a gas gun, a striker bar, an incident bar, and a transmitted bar, 12,20,24,52 was employed (Figure 4h). The initial high-speed stress wave (500 s −1 ) led to the elastic deformation of the SPN, exhibiting an ultrahigh modulus of ∼2 GPa (Figure 4i,j).…”

“…Furthermore, to examine the impact-stiffening behavior of the polyTA/arginine SPN in the high-speed regime, a split-Hopkinson pressure bar (SHPB) system, comprising a gas gun, a striker bar, an incident bar, and a transmitted bar, ,,, was employed (Figure h). The initial high-speed stress wave (500 s –1 ) led to the elastic deformation of the SPN, exhibiting an ultrahigh modulus of ∼2 GPa (Figure i,j).…”

“…To address this challenge, impact-stiffening materials have been developed as smart soft armors, retaining softness under quasi-static conditions while undergoing dramatic stiffening upon impact at high strain rates . Two notable examples include polyborosiloxanes (PBSs) or Silly Putty, which rely on rate-dependent B–O dative bonds, and shear-thickening fluids (e.g., cornstarch and silica suspensions), which operate based on a reentrant jamming transition. , To enhance their functionality, numerous efforts have focused on modifying their composition or hybridizing them with fillers/scaffolds. − Nevertheless, constrained by material type and rate-responsive mechanisms, the stiffening response of current impact-stiffening materials remains relatively low, with the storage modulus ( G ′) increase generally less than 1000 times within the typical shear frequency range of 0.1–100 Hz.…”