Content of SPECIAL TOPIC—Water at molecular level in our journal

Published in last 1 year |  In last 2 years |  In last 3 years |  All Please wait a minute... For selected: Download citations EndNote Ris BibTeX Toggle thumbnails Select Energy stored in nanoscale water capillary bridges formed between chemically heterogeneous surfaces with circular patches Bin-Ze Tang(唐宾泽), Xue-Jia Yu(余雪佳), Sergey V. Buldyrev, Nicolas Giovambattista§, and Li-Mei Xu(徐莉梅)¶ Chin. Phys. B, 2020, 29 (11): 114703.   DOI: 10.1088/1674-1056/abb664 Abstract （454）   HTML    PDF （955KB）（225）       Knowledge map    The formation of nanoscale water capillary bridges (WCBs) between chemically heterogeneous (patchy) surfaces plays an important role in different scientific and engineering applications, including nanolithography, colloidal aggregation, and bioinspired adhesion. However, the properties of WCB of nanoscale dimensions remain unclear. Using molecular dynamics simulations, we investigate the geometrical and thermodynamic properties of WCB confined between chemically heterogeneous surfaces composed of circular hydrophilic patches on a hydrophobic background. We find that macroscopic capillary theory provides a good description of the WCB geometry and forces induced by the WCB on the confining surfaces even in the case of surface patches with diameters of only 4 nm. Upon stretching, the WCB contact angle changes from hydrophobic-like values (θ > 90°) to hydrophilic-like values (θ < 90°) until it finally breaks down into two droplets at wall separations of ∼ 9–10 nm. We also show that the studied nanoscale WCB can be used to store relevant amounts of energy EP and explore how the walls patch geometry can be improved in order to maximize EP. Our findings show that nanoscale WCB can, in principle, be exploited for the design of clean energy storage devices as well as actuators that respond to changes in relative humidity. The present results can also be of crucial importance for the understanding of water transport in nanoporous media and nanoscale engineering systems. Select Fast and accurate determination of phase transition temperature via individual generalized canonical ensemble simulation Ming-Zhe Shao(邵明哲), Yan-Ting Wang(王延颋), Xin Zhou(周昕) Chin. Phys. B, 2020, 29 (8): 080505.   DOI: 10.1088/1674-1056/ab9c03 Abstract （714）   HTML    PDF （1914KB）（241）       Knowledge map    It is very important to determine the phase transition temperature, such as the water/ice coexistence temperature in various water models, via molecular simulations. We show that a single individual direct simulation is sufficient to get the temperature with high accuracy and small computational cost based on the generalized canonical ensemble (GCE). Lennard-Jones fluids, the atomic water models, such as TIP4P/2005, TIP4P/ICE, and the mW water models are applied to illustrate the method. We start from the coexistent system of the two phases with a plane interface, then equilibrate the system under the GCE, which can stabilize the coexistence of the phases, to directly derive the phase transition temperature without sensitive dependence on the applied parameters of the GCE and the size of the simulation systems. The obtained result is in excellent agreement with that in literatures. These features make the GCE approach in determining the phase transition temperature of systems be robust, easy to use, and particularly good at working on computationally expensive systems. Select Discontinuous transition between Zundel and Eigen for H5O2+ Endong Wang(王恩栋), Beien Zhu(朱倍恩), Yi Gao(高嶷) Chin. Phys. B, 2020, 29 (8): 083101.   DOI: 10.1088/1674-1056/ab973d Abstract （637）   HTML    PDF （1328KB）（133）       Knowledge map    The hydrated-proton structure is critical for understanding the proton transport in water. However, whether the hydrated proton adopts Zundel or Eigen structure in solution has been highly debated in the past several decades. Current experimental techniques cannot directly visualize the dynamic structures in situ, while the available theoretical results on the infrared (IR) spectrum derived from current configurational models cannot fully reproduce the experimental results and thus are unable to provide their precise structures. In this work, using H5O2+ as a model, we performed first-principles calculations to demonstrate that both the structural feature and the IR frequency of proton stretching, characteristics to discern the Zundel or Eigen structures, evolve discontinuously with the change of the O-O distance. A simple formula was introduced to discriminate the Zundel, Zundel-like, and Eigen-like structures. This work arouses new perspectives to understand the proton hydration in water.