Dynamic bonds as sticky friction in shear thickening dense suspensions

The discussion of frictional network formation has presented a new paradigm for understanding non-Newtonian shear-thickening behavior of dense suspensions. Recent studies have exclusively focused on volatile friction that instantaneously vanishes when the shear is ceased. We studied dense suspensions of thiol-functionalized particles suspended in ditopic polymers endcapped with benzalcyanoacetamide Michael-acceptors. The subsequent room temperature, catalyst free dynamic thia-Michael reactions can result in chemical friction between the particles when sheared, and the friction releases at the rest state. The frictional force can be tuned by the electronic nature of benzalcyanoacetamide moiety, and its relaxation strongly depends on the molecular weight of the ditopic polymers. These variables allow access to dense suspensions with a wide range of frictional force and stickiness. We found that such dynamic bond sticky friction drastically influences time-dependent rheology.