In the field of physics, negative pressure has always been a rare and challenging phenomenon to identify. However, thanks to the groundbreaking research conducted by the Quantum Optoacoustics research group at the Max Planck Institute for the Science of Light (MPL) in Erlangen, a new method to measure negative pressure has been discovered. Collaborating with the Leibniz Institute of Photonic Technologies in Jena (IPHT), the scientists have utilized liquid-filled optical fibers and sound waves to gain valuable insights into thermodynamic states.
Pressure, as a physical quantity, plays a crucial role in various fields such as meteorology, medicine, and everyday life. It is defined as the force per unit area acting perpendicular to the surface of a solid, liquid, or gas. Depending on the direction of the force within a closed system, high pressure can lead to explosive reactions, while low pressure can cause implosion. Under normal circumstances, pressure values are always positive. However, liquids possess a peculiar characteristic – they can exist in a metastable state with negative pressure values. This unique state of matter can be disrupted by even the slightest external influence. Imagine sitting at the top of a roller coaster, where the gentlest touch can send you hurtling down the tracks.
The researchers’ current study focuses on examining the metastable state of liquids with negative pressure. To achieve this, they combined two distinct techniques: encapsulating minuscule amounts of liquid in a closed optical fiber and utilizing the interaction of optical and acoustic waves in the liquid. This combination allowed for the precise measurement of the influence of pressure and temperature in different states of the liquid. Sound waves served as sensors to explore this unique state of matter with high precision and spatial resolution.
In the case of negative pressure, the laws of thermodynamics dictate that the volume of the liquid will decrease. However, the liquid is retained in the glass fiber capillary due to adhesive forces, similar to a water droplet sticking to a finger. This results in a “stretching” of the liquid, where it is pulled apart and behaves like a stretched rubber band.
In the past, measuring negative pressures required complex setups with extensive safety precautions, especially when using toxic liquids. However, the researchers developed a compact setup using light and sound waves for precise pressure measurements. This method eliminates the need for large laboratory spaces and minimizes disturbances to the metastable state of the system. The optical fiber used in the setup is as thin as a human hair. Dr. Birgit Stiller, the head of the Quantum Optoacoustics research group, expresses excitement about the possibilities that new measurement methods can provide for exploring difficult phenomena.
The Potential of Sound Waves
The sound waves utilised by the research group offer high sensitivity to changes in temperature, pressure, and strain along the optical fiber. These measurements can provide a spatially resolved image of the situation inside the fiber with centimeter-scale resolution. Alexandra Popp, one of the lead authors of the article, explains that this method allows for a deeper understanding of the thermodynamic dependencies within the fiber-based system. Andreas Geilen, another lead author, highlights the surprising effects observed in the measurements, particularly in the frequency of the sound waves.
The combination of optoacoustic measurements and tightly sealed capillary fibers opens up opportunities for monitoring chemical reactions in toxic liquids and investigating difficult-to-access materials and microreactors. This breakthrough provides access to high pressures and other thermodynamic regimes. It also offers the potential to explore and manipulate nonlinear optical phenomena in this type of fiber, unlocking new properties and states of materials that were previously unexplored.
With this new method to measure negative pressure, scientists can delve deeper into the mysteries of thermodynamics and gain unprecedented insights into the behavior of various materials. The implications of this research are vast, ranging from improved safety in pressure-related applications to advancements in our understanding of matter and its unique states.