最近人们认识到，液体黏度存在一个下限，该下限对所有液体几乎恒定，并由基本物理常数决定。这一点得到了稀有液体和分子液体实验数据的支持。在这里，我们开展大规模分子动力学模拟，以确定另外两种重要液体类型中的这一界限：离子熔盐体系 LiF 和金属 Pb。我们发现，这些离子体系和金属体系同样具有黏度下限，对应于约 10$^{-7}$ $\ rac{{\ m m}^2}{\ m s}$ 的运动黏度最小值。我们表明，这与其他具有不同结构和键合类型体系的实验数据一致，包括稀有液体、分子液体、金属液体和共价液体。这将黏度界限的普适性扩展到了已知的主要体系类型。
英文摘要：
Recently, it was realised that liquid viscosity has a lower bound which is nearly constant for all liquids and is governed by fundamental physical constants. This was supported by experimental data in noble and molecular liquids. Here, we perform large-scale molecular dynamics simulations to ascertain this bound in two other important liquid types: the ionic molten salt system LiF and metallic Pb. We find that these ionic and metallic systems similarly have lower viscosity bounds corresponding to the minimum of kinematic viscosity of about 10$^{-7}$ $\frac{{\rm m}^2}{\rm s}$. We show that this agrees with experimental data in other systems with different structures and bonding types, including noble, molecular, metallic and covalent liquids. This expands the universality of viscosity bounds into the main system types known.
Hydrogen bonding liquids, typically water and alcohols, are known to form labile structures (network, chains, etc...), hence the lifetime of such structures is an important microscopic parameter, which can be calculated in computer simulations. Since these cluster entities are mostly statistical in nature, one would expect that, in the short time regime, their lifetime distribution would be a broad Gaussian-like function of time, with a single maximum representing their mean lifetime, and weakly dependent on criteria such as the bonding distance and angle, much similarly to non-hydrogen bondin…
Hydrogen bonding is a phenomenon of paramount importance in room-temperature ionic liquids. The presence or absence of the hydrogen bond drastically alternates self-diffusion, shear viscosity, phase transition points, and other key properties of a pure substance. For certain applications, the presence of cation-anion hydrogen bonding is undesirable. In the present paper, we investigate perspectives of removing the hydrogen...fluorine interionic attraction in the imidazolium borates, the strongest non-covalent interaction in this type of system. Chemical modification of the tetrafluoroborate an…
The viscosity enhancement of a solvent produced by the addition of thickening branched polymers is predicted as a function of polymer concentration, branch length and persistence length, and strength of the covalent bonding interactions. Non equilibrium, stationary state Poiseuille numerical simulations are performed using the dissipative particle dynamics model to obtain the viscosity of the fluid. It is found that the clustering of the polymers into aggregates raises the viscosity and that it is more strongly affected by the strength of the bonding interactions. General scaling relationships…
Nucleation kinetics of vapor bubbles in a liquid with arbitrary viscosity
在[J. Phys. Chem. B 116，9445（2012）]中针对高粘度的情况开发的单组分液体中的蒸汽气泡成核的理论（（V，/rho，T）-理论）被扩展到任意粘度的情况。为此目的，朗之万的方法在理论的布朗运动，或Kramers的模型的化学反应，被雇用。所得到的气泡成核速率的表达式是有效的任意之间的关系的动力学参数控制的成核过程：粘度，液体的惯性，蒸发成气泡的速度和气泡和周围液体之间的热交换速率。因此，所提出的理论与（V，/rho，T）-理论一起给出了单组分液体中汽泡成核动力学的完整描述。考虑了上述参数的极限情况，特别是低粘度极限。结果表明，低粘度和高粘度的成核速率在定性和定量上彼此不同。讨论了该理论应用于超流氦-4空化的可能性。
Complexation of polymers at liquid interfaces is an emerging technique to produce all-liquid printable and self-healing devices and membranes. It is crucial to control the assembly process but the mechanisms at play remain unclear. Using two different reflectometric methods, we investigate the spontaneous growth of H-bonded PPO-PMAA membranes at a flat liquid-liquid interface. We find that the membrane thickness h grows with time t as h~t^(1/2), which is reminiscent of a diffusion-limited process. However, counter-intuitively, we observe that this process is faster as the PPO molar mass increa…
The response of Newtonian liquids to small perturbations is usually considered to be fully described by homogeneous transport coefficients like shear and dilatational viscosity. However, the presence of strong density gradients at the liquid/vapor boundary of fluids hints at the possible existence of an inhomogeneous viscosity. Here, we show that a surface viscosity emerges from the collective dynamics of interfacial layers in molecular simulations of simple liquids. We estimate the surface viscosity to be 8-16 times smaller than that of the bulk fluid at the thermodynamic point considered. Th…
The local intermolecular structure and related dynamics in the liquid cis-trans N-methylformamide mixture at ambient temperature and density conditions have been systematically studied by employing Born-Oppenheimer molecular dynamics simulation techniques. Particular attention has been paid to the local structure around the cis- and trans- conformers and the formation and dynamics of hydrogen bonds with their closest neighbors. The calculated atom-atom radial distribution functions are in very good agreement with available experimental data and reveal the existence of different types of hydrog…
We discuss hydrodynamic forces acting on a two-dimensional liquid domain that moves laterally within a supported fluid membrane in the presence of odd viscosity. Since active rotating proteins can accumulate inside the domain, we focus on the difference in odd viscosity between the inside and outside of the domain. Taking into account the momentum leakage from a two-dimensional incompressible fluid to the underlying substrate, we analytically obtain the fluid flow induced by the lateral domain motion, and calculate the drag and lift forces acting on the moving liquid domain. In contrast to the…
Viscosity ($η$) is one of the most important properties of disordered matter. The temperature-dependence of viscosity is used to adjust process variables for glass-making, from melting to annealing. The aim of this work was to develop a physics-informed machine learning model capable of predicting $η(T)$ of oxide liquids. Instead of predicting the viscosity itself, the NN predicts the parameters of the MYEGA viscosity equation: the liquid's fragility index, the glass transition temperature, and the asymptotic viscosity. With these parameters, $η$ can be computed at any temperature of interest,…
Recently, it has been found that the kinematic viscosity of liquids at the minimum, $ν_m$, can be expressed in terms of fundamental physical constants, giving $ν_m$ on the order of $10^{-7}~{\rm m^2/s}$. Here, we show that the kinematic viscosity of quark-gluon plasma (QGP) has a similar value and support this finding by experimental data and theoretical estimations. The similarity is striking, given that the dynamic viscosity and the density of QGP are about 16 orders of magnitude larger than in liquids and that the two systems have disparate interactions and fundamental theories. We discuss …
In the last few decades, theoretical and experimental studies of glass-forming liquids have revealed presence of universal regularities in the viscosity-temperature data. In the present work, we propose a viscosity model for scaling description of experimental viscosity data. A feature of this model is presence of only two adjustable parameters and high accuracy of experimental data approximation by this model for a wide temperature range. The basis of the scaling description is an original temperature scale. Within this scaling description we obtain the transformed Angell plot, in which the a…
Nanofluids; dispersions of nanometer-sized particles in a liquid medium; have been proposed for a wide variety of thermal management applications. It is known that a solid-like nanolayer of liquid of typical thickness 0.5-1 nm surrounding the colloidal nanoparticles can act as a thermal bridge between the nanoparticle and the bulk liquid. Yet, its effect on the nanofluid viscosity has not been elucidated so far. In this article, we compute the local viscosity of the nanolayer using equilibrium molecular dynamics based on the Green-Kubo formula. We first assess the validity of the method to pre…
Spectral Decomposition of Liquid Viscosity into Instantaneous Normal Modes
Institute of Mechanics, Chinese Academy of Sciences（中国科学院力学研究所）；University of Chinese Academy of Sciences（中国科学院大学）；The Chinese University of Hong Kong, Shenzhen（香港中文大学（深圳））；Shanghai Jiao Tong University（上海交通大学）
Liquids realize a highly complex state of matter in which strong competing kinetic and interaction effects come to life. As such, liquids are more challenging to understand than either gases or solids generally. In weakly interacting gases, the kinetic effects dominate. By contrast, low temperature solids typically feature far smaller fluctuations about their ground state. Notwithstanding their complexity, with the exception of quantum fluids and supercooled liquids, various aspects of common liquid dynamics such as their dynamic viscosity are often assumed to be given by rather simple, Arrhen…
Transport properties of dense fluids are fundamentally challenging, because the powerful approaches of equilibrium statistical physics cannot be applied. Polar fluids compound this problem, because the long-range interactions preclude the use of a simple effect-diameter approach based solely on hard spheres. Here, we develop a kinetic theory for dipolar hard-sphere fluids that is valid up to high density. We derive a mathematical approximation for the radial distribution function at contact directly from the equation of state, and use it to obtain the shear viscosity. We also perform molecular…
