Nanoparticles found to violate second law of thermodynamics
By Heidi Hoopes
April 3, 2014
It may be a little late for April Fool’s, but some skepticism is nonetheless warranted when reading that researchers have shown nanoparticles to disobey a fundamental law of physics which dictates the flow of entropy and heat in, it was believed, any situation. Specifically, researchers from three universities theoretically proposed then demonstrated that a nanoparticle in a state of thermal non-equilibrium does not always behave as larger particles might under the same conditions, with implications for various fields of research.
The second law of thermodynamics is the one that makes perpetual motion machines impossible. It states that the entropy – the measure for the disorder of a system – of any isolated system cannot decrease spontaneously, with the system evolving towards the state of maximum entropy (favoring disorder). The team has shown that a nanoparticle trapped with laser light temporarily violates this law. This seeming violation of universal law is transient, something that the researchers first derived as a mathematical model of fluctuations expected at the nanoscale.
To test their theorem, scientists at the University of Vienna, the Institute of Photonic Sciences in Barcelona and the Swiss Federal Institute of Technology in Zürich trapped a nanosized silica sphere with a radius of less than 75 nm in a laser "trap." Not only was the particle held in place, but could be precisely measured in three different directions, important when your particle is so small that 10,000 of them could line the width of a pinhead.
The nano-sphere was cooled lower than the temperature of the surrounding gas, creating a state of nonequilibrium. At a macro scale, a state of thermal non-equilibrium is what dictates that a snowman melts in a suddenly warming environment by absorbing heat from its surroundings, rather than growing more frozen by losing heat. A blindingly obvious example, yet at the nanoscale, such real-life observations are not without exception.
Indeed, by measuring the oscillations in the particle, the researchers were able to determine that the nanoparticle would, at times, effectively release heat to its warming surroundings rather than absorb heat.
Nanoparticles could range from natural parts within cells to man-made devices being developed in medicine and electronics. All of these particles experience random conditions due to their tiny scale. Both this experimental setup and the fluctuation theorem represent new ways to assess how nanoscale technology might fare when exposed to random environmental buffetings. Further studies are planned to further explore this phenomenon.
The research was originally published in Nature Nanotechnology.
Source: University of Vienna