Liquid or solid? a biologically inspired concentrated suspension for protective coating

Thermophiles can survive in a high-temperature environment due to the synergy of hydrophobic interaction and electrostatic interaction in their proteins. Shear thickening fluid (STF) is a kind of concentrated suspension, which shows shear thickening (ST) behavior and can transform from a liquid state to a solid state under shearing. However, this special phenomenon relies on the hydrogen bonds between particles and dispersing medium. At elevated temperatures, the hydrogen bonds will break and the ST effect will become weaker or even disappear. Herein, inspired by the high-temperature resistance mechanism of thermophile proteins, a novel MOF-801 based STF with better ST effect at elevated temperatures is reported. Specifically, the hydrogen bonds that conventional STF relies on are replaced with hydrophobic interaction and electrostatic interaction, adopting a strategy of dispersing MOF-801 into a mixture containing poly(ethylene glycol), poly(acrylic acid), and Ca2+. When the temperature rises to 55 degrees C, the storage modulus of M-STF rises from 13 Pa to 2036 Pa, and the suspension transforms to a solid-like state. Thus, a shapeable, self-healing, shear-stiffing, and conductive polymer-like substance can be obtained. In addition, a high-performance composite can be developed by impregnating M-STF into Kevlar, which shows promising applications in lightweight body protection.