Unexpected Solidlike Fracture in Simple Liquids.

Solids fracture under critical stress, while liquids exhibit continuous deformation. Viscoelastic liquids can fracture like solids when the deformation rate is high enough that the material's storage modulus G^{'} is approximately the same or higher than its loss modulus G^{''}. Here, we present direct experimental evidence of solidlike fracturing in hydrocarbon blend liquids whose G^{''} is an order of magnitude greater than G^{'} for the rates probed. In our experimental setup, high-viscosity simple liquids were subjected to shear and extensional flow. Fracture occurred at a total critical stress of 2(±1)  MPa for hydrocarbon blends and styrene oligomers, which interestingly remained independent of viscosity, chemical composition, temperature, and velocity. Near the crack-onset velocity, ductile cup-cone fractures are observed, whereas at higher deformation rates the fracture becomes predominantly brittle. To test the generality of this phenomenon, we repeated the experiments using a different simple liquid, styrene oligomer, at different temperatures and observed the same fracture behavior. Our findings suggest that fractures in liquids can occur independent of the relative dominance of viscous or elastic behavior. These findings expand our understanding of fracture mechanics beyond purely elastic-induced phenomena. Further research is warranted to explore the underlying mechanisms and practical implications.