Characterization of thin liquid films using molecular dynamics simulation

Various characteristics of a thin liquid film in its vapor-phase are investigated using the molecular dynamics technique. Local distributions of the temperature, density, normal and tangential pressure components, and stress are calculated for various film thicknesses and temperature levels. Distributions of local stresses change considerably with respect to film thicknesses, and interfacial regions on both sides of the film start to overlap with each other as the film becomes thinner. Integration of the local stresses, i.e., the surface tension, however, does not vary much regardless of the interfacial overlap. The minimum thickness of a liquid film before rupturing is estimated with respect to the calculation domain sizes and is compared with a simple theoretical relation.     

Molecular dynamics study on external field induced crystallization of amorphous argon structure

A molecular dynamics study has been conducted on an external-force-field-induced isothermal crystallization process of amorphous structures as a new low-temperature athermal crystallization process. An external cyclic-force field with a dc bias is imposed on molecules selected randomly in an amorphous-phase of argon. Multiple peaks smoothed out in the radial distribution functions for amorphous states appear very clearly during the crystallization process that cannot be achieved otherwise. When the amorphous material is locally exposed to an external force field, crystallization starts and propagates from the interfacial region and crystallization growth rates can be estimated.     

Molecular dynamics simulation of surface energy and ZDDP effects on friction in nano-scale lubricated contacts

Molecular dynamics simulations are used to study the tribological performance of a lubricant mixture containing hexadecane base oil and 5% zinc dithiophosphate (ZDDP) under molecular confinement conditions. The influence of ZDDP additive and the surface-lubricant interaction on the mechanical and thermal interfacial response are studied in detail. Results show that mechanical and thermal slips are reduced by increasing the surface energy. Simulations also demonstrate the migration of ZDDP molecules and their adsorption onto the solid surface resulting in a remarkable suppression of mechanical slip compared to pure hexadecane. Consequently, the effective shear rate is higher and so is the friction.     

渗金属气压对光电高温计测温精度影响的实验研究

为准确控制双辉等离子渗金属工件的温度,借助自制的一套热电偶测温实验装置,对光电高温计测温进行了比对实验,探讨了气压对光电高温计测温精度的影响。实验结果表明:在双辉等离子渗金属过程中,对同一工件温度,随工作气压的升高,光电高温计所用的ε值也增大。工作气压每增高5～10Pa,将ε值提高0 1,这时光电高温计的温度测量误差会小于±3℃。