方阱链流体在固液界面分布的密度泛函理论研究  

Studies on the density profiles of square-well chain fluid confined in a slit pore by density functional theory

作　　者：叶贞成[1] 蔡钧[1] 张书令[1] 刘洪来[1] 胡英[1] 

机构地区：[1]华东理工大学化学系,结构可控先进功能材料教育部重点实验室和化学工程国家重点实验室,上海200237

出　　处：《物理学报》2005年第9期4044-4052,共9页Acta Physica Sinica

基　　金：国家自然科学基金(批准号:20025618;20236010);上海市教委E研究院上海高校网格项目(批准号:200303);上海市教委资助的课题.~~

摘　　要：应用Yethiraj的加权密度近似泛函理论研究平板狭缝中方阱链流体的密度分布,系统的Helmholtz自由能泛函分为理想气体的贡献利剩余贡献两部分,其中剩余贡献部分分别采用刘洪来等人建立的基于空穴相关函数的方阱链流体状态方程和Gil_Villegas等人提出的统计缔合流体理论状态方程(SAFT_VR)结合简单加权密度近似计算.考察了不同链长、温度、系统密度和壁面吸引强度下平板狭缝中方阱链流体的密度分布,并与MonteCarlo(MC)模拟结果进行了比较.结果表明采用不同的状态方程对密度分布的计算有明显的影响,对于受限于硬壁狭缝中的方阱链流体,温度和密度比较高时,两种状态方程计算的结果均与MC模拟符合得比较好,在低温和低密度下效果变差,SAFT_VR方程的计算结果更接近于MC模拟结果.对于受限于方阱壁狭缝中的方阱链流体,由于系统密度分布的非均匀性加强,采用两种状态方程计算的结果均与MC模拟结果有一定偏差,寻找更合适的权重函数是进一步改进的关键.The density profiles of square-well chain fluid confined in two planar walls are calculated using density-functional theory based on the weighted-density approximation of Yethiraj. The free energy functional of the system consists of an ideal part and excess part. We obtain the excess part by the equation of state of corresponding uniform system combined with the weighted- density approximation. We adopted respectively the equations of state based on cavity correlation function and the statistically associating fluid theory. The calculated density profiles are compared with the corresponding Monte Carlo simulation data at different chain lengths, temperatures, volume fractions and different attractions of the wall. For a square-well chain fluid confined in two hard planar walls, results from both equations of state are in good agreement with that of the Monte Carlo simulations at high temperature and high volume fraction. Both results deviate from the Monte Carlo result at low temperature and low volume fraction. The density profile in hard wall slit pore calculated from the equation of state of SAFT-VR is in better agreement with the available simulation data than that from the equation of state developed by Liu et al. We find that the equation of state has significant influence on theoretical prediction. For the walls with attractive forces, predictions from both equations of state deviate from the simulation data. This deviation results from the increasing non-uniformity of the fluids. Therefore, more suitable weighted-density function is needed to improve the density - functional theory.

关 键 词：密度泛函理论 非均匀流体 密度分布 固液界面 方阱链 统计缔合流体理论 密度泛函 理论研究 链长 面分布 状态方程 近似计算 

分 类 号：O351[理学—流体力学]