Sloutskin E, Wu X Z, Peterson T B, Gang O, Ocko B M, Sirota E B, Deutsch M
Physics Department, Bar Ilan University, Ramat Gan 52900, Israel.
Phys Rev E Stat Nonlin Soft Matter Phys. 2003 Sep;68(3 Pt 1):031605. doi: 10.1103/PhysRevE.68.031605. Epub 2003 Sep 23.
X-ray surface scattering and surface tension measurements are used to study surface freezing in molten mixtures of alkanes. These binary mixtures consist of protonated and deuterated alkanes, as well as of alkanes of different lengths. As for pure alkanes, a crystalline monolayer is formed at the surface a few degrees above the bulk freezing temperature. The structure of the monolayer has been determined on an angstrom scale. A simple theoretical approach is used to account for the thermodynamical observations at the surface and in the bulk. The model is based on a competition between entropic mixing and a repulsive interaction due to chain-length mismatch. The surface and bulk liquid phases are treated as ideal mixtures, while the solid phases are treated as regular mixtures. The theory is found to account well for all the mixtures studied, both hydrogenated-hydrogenated and hydrogenated-deuterated. The repulsive interaction and its dependence on the chain lengths of the components are determined from fits to the measured data.
利用X射线表面散射和表面张力测量来研究烷烃熔融混合物中的表面冻结现象。这些二元混合物由质子化和氘代烷烃以及不同长度的烷烃组成。与纯烷烃一样，在高于本体冻结温度几度时，表面会形成一个晶体单层。已在埃尺度上确定了单层的结构。采用一种简单的理论方法来解释表面和本体的热力学观测结果。该模型基于熵混合与由于链长不匹配引起的排斥相互作用之间的竞争。表面和本体液相被视为理想混合物，而固相被视为正规混合物。发现该理论能很好地解释所研究的所有混合物，包括氢化-氢化和氢化-氘代混合物。通过对测量数据的拟合确定排斥相互作用及其对组分链长的依赖性。
