Not found SPECIAL TOPIC — Water at molecular level

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    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
    Abstract711)   HTML    PDF (1914KB)(241)      

    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.

    Rules essential for water molecular undercoordination
    Chang Q Sun(孙长庆)
    Chin. Phys. B, 2020, 29 (8): 088203.   DOI: 10.1088/1674-1056/ab8dad
    Abstract465)   HTML    PDF (3431KB)(165)      

    A sequential of concepts developed in the last decade has enabled a resolution to multiple anomalies of water ice and its low-dimensionality, particularly. Developed concepts include the coupled hydrogen bond (O:H-O) oscillator pair, segmental specific heat, three-body coupling potentials, quasisolidity, and supersolidity. Resolved anomalies include ice buoyancy, ice slipperiness, water skin toughness, supercooling and superheating at the nanoscale, etc. Evidence shows consistently that molecular undercoordination shortens the H-O bond and stiffens its phonon while undercoordination does the O:H nonbond contrastingly associated with strong lone pair “:” polarization, which endows the low-dimensional water ice with supersolidity. The supersolid phase is hydrophobic, less dense, viscoelastic, thermally more diffusive, and stable, having longer electron and phonon lifetime. The equal number of lone pairs and protons reserves the configuration and orientation of the coupled O:H-O bonds and restricts molecular rotation and proton hopping, which entitles water the simplest, ordered, tetrahedrally-coordinated, fluctuating molecular crystal covered with a supersolid skin. The O:H-O segmental cooperativity and specific-heat disparity form the soul dictate the extraordinary adaptivity, reactivity, recoverability, and sensitivity of water ice when subjecting to physical perturbation. It is recommended that the premise of “hydrogen bonding and electronic dynamics” would deepen the insight into the core physics and chemistry of water ice.

    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
    Abstract636)   HTML    PDF (1328KB)(133)      

    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.

    Effects of water on the structure and transport properties of room temperature ionic liquids and concentrated electrolyte solutions
    Jinbing Zhang(张晋兵), Qiang Wang(王强), Zexian Cao(曹则贤)
    Chin. Phys. B, 2020, 29 (8): 087804.   DOI: 10.1088/1674-1056/ab9c07
    Abstract696)   HTML    PDF (2100KB)(326)      

    Transport properties and the associated structural heterogeneity of room temperature aqueous ionic liquids and especially of super-concentrated electrolyte aqueous solutions have received increasing attention, due to their potential application in ionic battery. This paper briefly reviews the results reported mainly since 2010 about the liquid-liquid separation, aggregation of polar and apolar domains in neat RTILs, and solvent clusters and 3D networks chiefly constructed by anions in super-concentrated electrolyte solutions. At the same time, the dominating effect of desolvation process of metal ions at electrode/electrolyte interface upon the transport of metal ions is stressed. This paper also presents the current understanding of how water affects the anion-cation interaction, structural heterogeneities, the structure of primary coordination sheath of metal ions and consequently their transport properties in free water-poor electrolytes.

    Atomic-level characterization of liquid/solid interface
    Jiani Hong(洪嘉妮) and Ying Jiang(江颖)
    Chin. Phys. B, 2020, 29 (11): 116803.   DOI: 10.1088/1674-1056/aba9d0
    Abstract473)   HTML    PDF (2242KB)(410)      

    The detailed understanding of various underlying processes at liquid/solid interfaces requires the development of interface-sensitive and high-resolution experimental techniques with atomic precision. In this perspective, we review the recent advances in studying the liquid/solid interfaces at atomic level by electrochemical scanning tunneling microscope (EC-STM), non-contact atomic force microscopy (NC-AFM), and surface-sensitive vibrational spectroscopies. Different from the ultrahigh vacuum and cryogenic experiments, these techniques are all operated in situ under ambient condition, making the measurements close to the native state of the liquid/solid interface. In the end, we present some perspectives on emerging techniques, which can defeat the limitation of existing imaging and spectroscopic methods in the characterization of liquid/solid interfaces.

    Water on surfaces from first-principles molecular dynamics
    Peiwei You(游佩桅), Jiyu Xu(徐纪玉), Cui Zhang(张萃), and Sheng Meng(孟胜)$
    Chin. Phys. B, 2020, 29 (11): 116804.   DOI: 10.1088/1674-1056/aba279
    Abstract519)   HTML    PDF (1229KB)(357)      

    Water is ubiquitous and so is its presence in the proximity of surfaces. To determine and control the properties of interfacial water molecules at nanoscale is essential for its successful applications in environmental and energy-related fields. It is very challenging to explore the atomic structure and electronic properties of water under various conditions, especially at the surfaces. Here we review recent progress and open challenges in describing physicochemical properties of water on surfaces for solar water splitting, water corrosion, and desalination using first-principles approaches, and highlight the key role of these methods in understanding the complex electronic and dynamic interplay between water and surfaces. We aim at showing the importance of unraveling fundamental mechanisms and providing physical insights into the behavior of water on surfaces, in order to pave the way to water-related material design.

    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
    Abstract453)   HTML    PDF (955KB)(225)      

    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.

    Evaporation of nanoscale water on solid surfaces
    Rongzheng Wan(万荣正) and Haiping Fang(方海平)
    Chin. Phys. B, 2020, 29 (12): 126601.   DOI: 10.1088/1674-1056/abc0d3
    Abstract427)   HTML    PDF (1408KB)(297)      
    The evaporation of water is essential in the macroscopic world. Recent researches show that, on solid surfaces, the evaporation of nanoscale water is quite different from that on bulk water surfaces. In this review, we show the theoretical progress in the study of nanoscale water evaporation on various solid surfaces: the evaporation rate of nanoscale water does not show a monotonic decrease when the solid surface changes from hydrophobic to hydrophilic; the evaporation of nanoscale water on hydrophobic-hydrophilic patterned surfaces is unexpectedly faster than that on uniform surface; the evaporation of nanoscale water on patterned graphene oxide is faster than that on homogeneous one; how temperature affects the evaporation of nanoscale water on solid surface; how ions affect the evaporation of nanoscale water on graphene oxide.