At the most fundamental levels, science often challenges common sense. And a new finding might be the most nonsensical of them all: liquids break.<\/p>\n
A recent Physical Review Letters<\/a> paper, \u201cUnexpected Solidlike Fracture in Simple Liquids,\u201d reports observing exactly that\u2014when liquids are stretched with enough force, the supposedly fluid material fractures like a solid object. The findings suggest that viscosity<\/a>, or a liquid\u2019s resistance to flowing, may play a greater role in the mechanical properties of liquids than we believed. What\u2019s more, this behavior likely applies to very common liquids, like water or oil, raising new considerations for manipulating liquids across various applications.<\/p>\n \u201cWhat we observed was so unexpected that we needed to repeat the experiments a few more times to make sure it was real,\u201d Nicolas Alvarez, study co-author and an engineer at Drexel University, said in a statement<\/a>. \u201cThis fundamentally changes our understanding of fluid dynamics.\u201d<\/p>\n Not an equipment issue <\/p>\n The fancy way of describing fractures is to refer to the balance between surface energy and elastic energy release that results in a new interface. More simply, fractures appear when the energy released by a material exceeds the energy required to create a new surface. This is a defining trait that \u201cdefines solids\u201d but not liquids, which \u201cyield and flow rather than deform elastically under stress,\u201d according to the paper.<\/p>\n The researchers were initially studying this yielding and flowing behavior in tar-like hydrocarbon blends. What they expected to see was something like the \u201cdrawn-out thinning behavior familiar to anyone who\u2019s dolloped a glob of honey into a cup of tea,\u201d according to the statement. Then they heard the noise.<\/p>\n \u201cThe fracture caused a very loud snapping noise that actually startled me,\u201d recalled Thamires Lima, the study\u2019s lead author and an engineer at Drexel. \u201cI thought at first the machine had broken but soon realized that the noise came from the stretching fluid.\u201d<\/p>\n Cracking the cracks <\/p>\n According to Lima, the noise resulted in the team pivoting to \u201can entirely different scientific endeavor.\u201d Once they verified that the noise didn\u2019t come from any equipment failures, the researchers designed experiments to check for similar behavior in liquids with the same viscosity as the hydrocarbons. A high-speed camera recorded each session, giving the team a detailed look into how things unfolded.<\/p>\n Fascinatingly, the liquids showed a consistent pattern of stretching until reaching a \u201ccritical stress\u201d point, at which they simply broke in half. This threshold measured up to\u00a02 megapascals, which is equivalent to the \u201ctension you\u2019d unpleasantly experience if you pushed a laundry bag containing 10 bricks off a ledge and its drawstring snagged on your fingernail,\u201d they explained.<\/p>\n This pattern persisted even as temperature shifts adjusted the viscosity, the team reported. The liquid fracture remained proportional to 2 megapascals until each sample\u2019s viscosity dropped low enough such that the equipment, which has a limited stretching capacity, wasn\u2019t able to stretch it any further.<\/p>\n A liquid\u2019s breaking point <\/p>\n The findings challenge the consensus that fracturing is a property of elasticity<\/a>, or a material\u2019s ability to hold stress. So far, scientists believed that elasticity more or less applied only to solids or to liquids cooled enough such that they started becoming solid-like. But the new study demonstrates that simple liquids with enough viscosity are \u201cenough to promote solid-like fracture behavior,\u201d Lima said.<\/p>\n