Research reveals that nanoparticles can break the rules of thermodynamic: what do these findings imply?
Are you an undergraduate who will soon approach the end of semester Thermodynamic exam? Stop studying immediately!
Last week popular scientific websites were full of the “big” news: nanoparticles violate the second rule of thermodynamics. It made me eager to read the original paper, published in Nature Nanotechnology, a journal on which many scientists long to have a paper in. After all the excitement I found out that the news was not a big deal for physicists. In fact, the same findings were already published in 2002. But why then was the new research accepted by one of the Gods of Scientific Journals if the discovery was first revealed more than ten years ago? I sincerely wanted to grab the deep and true meaning of the new research and decided to contact Prof. Lukas Novotny, from ETH Zürich, who was involved in the brand new study.
Prof. Novotny immediately confirmed that it is impossible to apply the traditional thermodynamics rules in every situation: «Thermodynamics consists of statistical descriptions, where you have a lot of impacts between molecules and therefore random collisions between them. Therefore, the second rule of thermodynamics describes an average behavior. However, when you have only one collision, there is no statistics anymore». Thus, the interesting and exceptional point is another one. Was it planned?
Surprisingly, he did not expect such a high scientific impact when the team started the project: «In fact, it all started with unexpected results from some measurements». The research group was using a standard experimental set- up, called laser tweezers, where a nanoparticle is trapped by a tightly focused laser beam. In general, the experiment is carried out in a liquid environment, so that the damping forces make the particle stay in the trap. In this case, the researchers substituted the liquid with high vacuum. This means that there is no friction anymore, «it is like a skateboard on a halfpipe: if there is no friction, the skateboard arrives on the other side of the halfpipe with the same speed». Hence, in order to slow down the particle in absence of friction, the scientists opted for a cooling mechanism.
Then, the weird started: «We wanted to assess how the particle re- heated, and every time it behaved differently. The traditional fluctuation theorem did not work because it is based on heat generation. That’s when one member of the team got involved developing a more detailed model. The new model was related to the entropy production, instead».
But when one research question is solved, further challenges disclose. So what would be the next steps? «Different directions are possible: we can try to further cool the system or we can analyze the particle hop between two traps and use such a “macroscopic” object to play at the interface of quantum mechanics and gravitation». In any case, the setting developed provides the scientists «an almost infinite time to play around with different parameters». Such high level of control is, indeed, what mostly excites Novotny.
The future will bring more experiments and maybe further discoveries of nanoparticles’ innovative properties and behaviors. But there is good news for students: you are not likely to have a new “Physic of Nanoparticles” course. Prof. Novotny’s states that all these new finding will not develop into a «separate field, but would rather enter into different fields, like biochemistry etc.». So, no further exams, but why don’t you try and impress your Thermodynamic professor by reporting such paper?
Photo: Flickr, Tyler J. Bolker
Gieseler J, Quidant R, Dellago C, & Novotny L (2014). Dynamic relaxation of a levitated nanoparticle from a non-equilibrium steady state. Nature nanotechnology PMID: 24681775
Wang, G., Sevick, E., Mittag, E., Searles, D., & Evans, D. (2002). Experimental Demonstration of Violations of the Second Law of Thermodynamics for Small Systems and Short Time Scales Physical Review Letters, 89 (5) DOI: 10.1103/PhysRevLett.89.050601
nanoparticles, thermodynamic, molecule, experiment, Nature, property, behavior