Ultra-accelerated quantum chemical molecular dynamics study on the calculation of viscosities of complex liquids

摘要

Ionic liquids (or room temperature molten salts) constitute a new class of substances that are considered as potential substitutes to many traditional organic solvents in reaction and separation processes. Ionic liquids are expected to be 'green solvent' in many of chemical industry, such as synthetic chemistry and electrochemistry and tribological applications, due to their unique physical and chemical properties. Needless to say, the properties of ionic liquids are useful for lubricants. To design any process involving ionic liquids on an industrial scale, it is necessary to know a range of physical properties including viscosity and density. Viscosity is one of the important factors in the characterization of lubricant performance. Molecular simulations have proven useful in understanding the physical properties of a fluid and its structure and composition that produce the desired macroscopic properties. Hence, in order to establish a new screening method for designing and characterization of new lubricants with desired physical properties, we have developed a new computational chemistry approach for the viscosity prediction of lubricants that based on the "Falling-ball" principles using classical molecular dynamics method. Our new computational method was applied to simple organic liquids at room conditions and complex lubricants under extreme conditions. This method was recently applied to calculate the viscosities of the complex ionic liquids using ultra-accelerated quantum molecular dynamics simulations. However, in this study, the calculated viscosities for the three kinds of ionic liquids are improved and much better accuracy is obtained. Calculated viscosities showed very good agreement with experimentally reported values. Results of the viscosity calculations for simple organic liquids are also indicated to show our methodology to be an effective tool for evaluating viscosity of complex liquids.