The classical nucleation theory does not give a clear description of the formation of the nucleus and the interfacial properties between the nucleus and the bulk phase are the same as that of macroscopic liquid vapor interface. The latter hypothesis resulted in considerable difference of the nucleation rate predicted by the theory from that experimentally measured. In this paper a model of two-region structure of a nucleus is proposed to describe nucleus evolution. The nucleus is composed of a central region and a transition region. The central region with radius r 1, can be regarded as a pure vapor region with density ρ v. Meanwhile, the transition region surrounds the central region, and its density varies linearly from ρ v of the central region at r 1, to ρl of the bulk liquid phase at r 2.The active molecules first aggregate and grow up in the transition region, which convert into vapor phase close to the boundary of the central region and aggregate inside the central region. When the transition region approximately decreases to a thickness of several molecular spacings,normal geometrical liquid-vapor interface is formed, the evolution of the nucleus completes and an ultimate vapor bubble with stable liquid-vapor interface is generated.With the interfacial tension calculated by using this model, the predicted nucleation rate is very close to the experimental measurement. Furthermore, this model and associated analysis provide solid theoretical evidence to clarify the definition of nucleation rate and understand nucleation phenomenon with the insight into the physical nature.
采用润滑近似分析完全浸润流体低毛细数下的动态湿润过程.结果表明,van der Waals长程相互作用力对表观接触线附近的液膜厚度场有重要影响,对于排斥的van der Waals力,膨胀压力大于零,自由界面上气相压力高于液相压力,液膜厚度随van der Waals力的增大而增大.毛细数对液膜厚度的影响表现为毛细数越大,液膜越厚.
Based on assuming that there is the precursor film in the front of the apparent contact line （ACL）, a model was proposed to understand the dynamic wetting process and associated dynamic contact angle. The present model indicated that a new dimensionless characteristic parameter, 2, attects the dynamic wetting process and associated dynamic contact angle as well. However, the previous model suggested that the dynamic contact angle is dependent＇on the capillary number and static contact angle only. An experimental investigation was conducted to measure the dynamic wetting behavior of silicon oil moving over glass, aluminum and stainless steel surfaces. It concluded that when the value of 2 was selected as 0.07, 0.16 and 0.35 for glass, aluminum and stainless steel, respectively, the experimental results were in good accordance with the prediction of the model. Furthermore, the comparison of the model with Strom＇s experimental data showed that 2 is independent on the species of liquids. Apparently, 2 should be interpreted as the effect of the solid surface properties on the dynamic wetting process.Meanwhile, it is found in the present experiment that the Hoffman-Voinov-Tanner law, which is valid at very low capillary number （Ca 〈〈 1 or 80〈 10°） recommend by Cazabat, still holds for higher contact angles, even up to 70°-80°. This is explained by （he present model very well.
