Recently, the team from the Institute of Nanoscience, School of Aeronautics and Astronautics of our university has made important progress in the research of micro-nano confined water. The results were published online in the National Science Review under the title An Analog of Friedel Oscillations in Nanoconfined water.
Research in physics, mechanics and other fields generally starts from the ideal system, but the behavior of the actual system is usually disturbed by defects, impurities and so on. Thus, attempts have been made to understand the effects of local disturbances caused by defects, impurities, etc., on systems of (quasi-) particles (such as Fermi liquids, most typically electrons in metals) and to find that electrons, etc., produce interesting density oscillations (figure below). This phenomenon is known as Friedel oscillations and is a manifestation of quantum effects. In the one-dimensional constrained system, the interaction between fermions becomes prominent, making the Behavior of Friedel oscillations more significant.
Figure 1. Positively charged impurities on the metal surface cause electron density to produce Friedel oscillations.
Similarly, this behavior shift caused by dimensionality reduction is also common in molecularly confined systems, such as the phase transition of low-dimensional confined water. The study of low-dimensional confined water can not only promote the development of micro-nanocrystalline devices, but also help to understand the transport of biomass. On the other hand, natural or synthetic nanoscale confined water systems are often disturbed by uneven pore surface, chemical modification, adsorbed impurities, and uneven charge. Could molecular systems behave like the Fredel oscillations of quantum systems?
Recently, the team from the Institute of Nanoscience of our university studied the structure and dynamic behavior of one-dimensional confined water under local disturbance based on large-scale molecular dynamics simulation, revealing the quantum veil of confined water -- like Friedel oscillation. It is found that the one-dimensional confined water density oscillates significantly in the axial direction under local perturbation and attenuates with distance, which is very similar to the Behavior of Friedel oscillation in quantum system. Moreover, their simulations show that this phenomenon exists in different forms of perturbation systems and echoes the oscillations of quantum systems in many characteristics. The team further developed a physical-mechanical model to demonstrate that the intensity and decay rate of such Friedell-like oscillations depend on the intensity of the disturbance and the dipole correlation of water molecules, respectively. More strikingly, the oscillations of the molecular density of the confined water can exert repulsive forces on the ions in the channel, thus blocking ion transport remotely. This has a unique regulation effect on ion transport in confined solution, which not only brings a new understanding of signal transmission in biological system, but also has a broad application prospect in seawater desalination and other fields.
Figure 2. (a) The axial density of one-dimensional confined water under local perturbations produces a Fredel-like oscillation. (b) The ion blocking behavior is caused by the Fredel-like oscillation in one-dimensional confined water.
The above research results reveal the little-known quantum-like behavior of confined water and open up a new way of mass transfer regulation of micro-nano confined fluids. The first author of this paper is Dr. Xue Minmin, corresponding author is Professor Zhang Zhuhua and Academician Guo Wanlin. The co-authors also include Professor Qiu Hu, Dr. Hu Zhili and Dr. Shen Chun.
Link：https://academic.oup.com/nsr/advance-article/doi/10.1093/nsr/nwab214/6446008?searchresult=1