Sloutskin E, Gang O, Kraack H, Doerr A, Sirota E B, Ocko B M, 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):031606. doi: 10.1103/PhysRevE.68.031606. Epub 2003 Sep 23.
Surface freezing is studied in dry and hydrated alcohol mixtures by surface x-ray scattering and surface tension measurements. A crystalline bilayer is formed at the surface a few degrees above the bulk freezing temperature. The packing is hexagonal, with molecules aligned along the surface normal in all cases. The in-plane lattice constant reveals a qualitatively different behavior with composition for hydrated and dry mixtures. The simple theoretical approach used successfully for alkane and deuterated alkane mixtures accounts well also for the alcohol mixtures. The repulsive length-mismatch term opposing the mixing entropy term in the free energy of the mixtures is shown to have a universal behavior for all mixtures studied: protonated alkanes, deuterated alkanes, and dry and wet alcohols. This universality is somewhat counterintuitive in view of the different interactions (e.g., hydrogen bonding in alcohols) in the different mixtures.
通过表面X射线散射和表面张力测量研究了干燥和水合醇混合物中的表面冻结现象。在高于本体冻结温度几度时，表面形成了一个结晶双层。堆积方式为六方晶系，在所有情况下分子都沿表面法线排列。面内晶格常数显示，水合混合物和干燥混合物的组成行为在定性上有所不同。成功用于烷烃和氘代烷烃混合物的简单理论方法也很好地适用于醇混合物。在混合物的自由能中，与混合熵项相反的排斥长度失配项对于所有研究的混合物（质子化烷烃、氘代烷烃以及干燥和湿润的醇）都表现出普遍行为。鉴于不同混合物中存在不同的相互作用（例如醇中的氢键），这种普遍性有点违反直觉。
