Study of the thermal diffusion behavior of alkane/benzene mixtures by thermal diffusion forced rayleigh scattering experiments and lattice model calculations.
Study of the thermal diffusion behavior of alkane/benzene mixtures by thermal diffusion forced rayleigh scattering experiments and lattice model calculations.
复制标题
通过热扩散强迫瑞利散射实验和晶格模型计算研究烷烃/苯混合物的热扩散行为。
DOI：
10.1021/jp065825v
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发表时间：
2006
期刊：
影响因子：
--
通讯作者：
S. Wiegand
中科院分区：
文献类型：
--
作者：
P. Polyakov;J. Luettmer;S. Wiegand
采用热扩散强迫瑞利散射（TDFRS）方法研究了不同浓度和温度下直链烷烃（庚烷、壬烷、十一烷、十三烷、十五烷、十七烷）在苯中的热扩散行为。的Soret系数ST的烷烃被发现是负的，这些正烷烃/苯的混合物，表明烷烃富集在较温暖的区域的液体混合物。对于在这项工作中调查的组合物，Soret系数的大小随着链长的增加和混合物的烷烃含量的增加而减小。Soret系数的温度依赖性取决于混合物的组成和烷烃链长; ST随温度变化的斜率随着中间组合物链长的增加而从正变为负。为了研究分子结构对Soret效应的影响，还研究了支链烷烃（2-甲基己烷、3-甲基己烷、2，3-二甲基戊烷、2，4-二甲基戊烷、2，2，3-三甲基丁烷和2，2，4-三甲基戊烷）在苯中的混合物。我们的Soret系数的结果表明，烷烃移动到温暖的流体区域的趋势随着分支度的增加而降低。支化效应是如此之强，对于2，2，4-三甲基戊烷/苯混合物的Soret系数在高烷烃含量下改变符号，并且等摩尔的2，2，3-三甲基丁烷/苯混合物在所研究的温度范围内具有正的Soret系数。为了研究分子相互作用对热扩散的影响，我们采用了最近开发的双室晶格模型，正烷烃/苯混合物。该模型包括链长，可压缩性，苯-苯相互作用的取向依赖性的影响，并产生良好的定性预测的Soret效应在正烷烃/苯混合物。对于支化异构体，我们发现分子的转动惯量和Soret系数之间存在一定的相关性。PACS编号：66.10.Cb，61.25.Hq。
In this work the thermal diffusion behavior of binary mixtures of linear alkanes (heptane, nonane, undecane, tridecane, pentadecane, heptadecane) in benzene has been investigated by thermal diffusion forced Rayleigh scattering (TDFRS) for a range of concentrations and temperatures. The Soret coefficient ST of the alkane was found to be negative for these n-alkane/benzene mixtures indicating that the alkanes are enriched in the warmer regions of the liquid mixtures. For the compositions investigated in this work, the magnitude of the Soret coefficient decreases with increasing chain length and increasing alkane content of the mixtures. The temperature dependence of the Soret coefficient depends on mixture composition and alkane chain length; the slope of ST versus temperature changes from positive to negative with increasing chain length at intermediate compositions. To study the influence of molecular architecture on the Soret effect, mixtures of branched alkanes (2-methylhexane, 3-methylhexane, 2,3-dimethylpentane, 2,4-dimethylpentane, 2,2,3-trimethylbutane, and 2,2,4-trimethylpentane) in benzene were also investigated. Our results for the Soret coefficients show that the tendency for the alkanes to move to the warmer regions of the fluid decreases with increasing degree of branching. The branching effect is so strong that for 2,2,4-trimethylpentane/benzene mixtures the Soret coefficient changes sign at high alkane content and that equimolar 2,2,3-trimethylbutane/benzene mixtures have positive Soret coefficients in the investigated temperature range. In order to investigate the effect of molecular interactions on thermal diffusion, we adapted a recently developed two-chamber lattice model to n-alkane/benzene mixtures. The model includes the effects of chain-length, compressibility, and orientation dependence of benzene-benzene interactions and yields good qualitative predictions for the Soret effect in n-alkane/benzene mixtures. For the branched isomers, we find some correlations between the moments of inertia of the molecules and the Soret coefficients. PACS numbers: 66.10.Cb, 61.25.Hq.