Photothermally-Induced Reversible Rigidity of Nacre-Mimetic Composites Toward Semi-Active Personal Safeguard

Abstract

The capacity to withstand challenges posed by complex environments is crucial for developing advanced high-performance protective materials with mechanically adjustable nature. By constructing long-range hierarchical network of shear-stiffening gel-carbon nanotube-cellulose nanofiber (SCC) embedded within epoxy resin (ER), this work engineers a nacre-inspired variable-stiffness SCC-ER composite (SCCE). Lightweight SCC scaffold attenuates falling impact force from 2.23 to 0.46 kN, and reaches 60 °C within 20 s under 1 sun exposure. Additionally, owing to the rigid ER matrix, SCCE exhibits 4.03 GPa elastic modulus, outperforming numerous conventional engineering materials in puncture resistance. Specific energy absorption of nacre-mimetic SCCE presents 1.91 MJ m⁻³ while that of random structural SCCE is only 0.50 MJ m⁻³. More importantly, SCCE features representative photothermal-induced reversible rigidity whose storage modulus varies from 9.85 MPa at 30 °C to 11.61 kPa at 116 °C under light stimulation. It also presents shape-programmability, capable of adhering complex structural surfaces for protection. Eventually, SCCE-based semi-active adjustable protectors are constructed that leverage contactless photothermal effect to modulate rigidity. 5 mm-thick smart SCCE-protectors resist 163.93 m s⁻¹ ballistic impact while 15-mm commercial kneepads are penetrated at lower speed of 136.98 m s⁻¹. This bio-inspired semi-active strategy proposes a promising avenue for enhancing personal protective equipment.