Negative pressure is a rare and challenging-to-detect phenomenon in physics. Using liquid-filled optical fibers and sound waves, researchers at the Max Planck Institute for the Science of Light (MPL) in Erlangen have now discovered a new method to measure it. In collaboration with the Leibniz Institute of Photonic Technologies in Jena (IPHT), the scientists in the Quantum Optoacoustics research group, led by Birgit Stiller, can gain important insights into thermodynamic states.
As a physical quantity pressure is encountered in various fields: atmospheric pressure in meteorology, blood pressure in medicine, or even in everyday life with pressure cookers and vacuum-sealed foods. Pressure is defined as a force per unit area acting perpendicular to a surface of a solid, liquid, or gas. Depending on the direction in which the force acts within a closed system, very high pressure can lead to explosive reactions in extreme cases, while very low pressure in a closed system can cause the implosion of the system itself.
Overpressure always means that the gas or liquid pushes against the walls of its container from the inside, like a balloon expanding when more air is added. Regardless of whether it’s high or low pressure, the numerical value of pressure is always positive under normal circumstances.
However, liquids exhibit a peculiar characteristic. They can exist in a specific metastable state corresponding to a negative pressure value. In this metastable state, even a tiny external influence can cause the system to collapse into one state or another. One can imagine it as sitting at the top of a roller coaster: the slightest touch on one side or the other sends you hurtling down the tracks. In their current research, the scientists are examining the metastable state of liquids with negative pressure.
To achieve this, the research team combined two unique techniques in a study published in Nature Physics to measure various thermodynamic states. Initially, tiny amounts—nanoliters—of a liquid were encapsulated in a fully closed optical fiber, allowing both highly positive and negative pressures. Subsequently, the specific interaction of optical and acoustic waves in the liquid enabled the sensitive measurement of the influence of pressure and temperature in different states of the liquid.
2023-09-25 13:48:02
Link from phys.org