液态正己烷在二氧化硅纳米通道中的凝聚：光学双折射和蒸气吸附等温线的联合研究
Liquid n-hexane condensed in silica nanochannels: A combined optical birefringence and vapor sorption isotherm study
摘要：
本文研究了正己烷在直径为7nm、长度为400 μ m的平行石英通道中的光学双折射随气相填充量的变化。通过与广义Bruggeman有效介质方程的分析，我们证明，这样的测量是不敏感的详细的几何（位置）排列的通道内的吸附液体。然而，这种技术特别适合于搜索任何光学各向异性，因此集体取向顺序作为通道填充的函数。然而，在液体正己烷中没有发现这种各向异性的迹象。二氧化硅纳米通道中的正己烷分子在所有冷凝制度中，特别是在膜生长以及在毛细管冷凝制度中是完全取向无序的。因此，在纳米通道限制中冷冻液体正己烷时发现的特殊分子排列，其中分子垂直于通道的长轴集体排列，并不源于由于毛细管线化而在纳米限制液体中的任何预排列效应。
英文摘要：
The optical birefringence of liquid n-hexane condensed in an array of parallel silica channels of 7nm diameter and 400 micrometer length is studied as a function of filling of the channels via the vapor phase. By an analysis with the generalized Bruggeman effective medium equation we demonstrate that such measurements are insensitive to the detailed geometrical (positional) arrangement of the adsorbed liquid inside the channels. However, this technique is particularly suitable to search for any optical anisotropies and thus collective orientational order as a function of channel filling. Nevertheless, no hints for such anisotropies are found in liquid n-hexane. The n-hexane molecules in the silica nanochannels are totally orientationally disordered in all condensation regimes, in particular in the film growth as well as in the the capillary condensed regime. Thus, the peculiar molecular arrangement found upon freezing of liquid n-hexane in nanochannel-confinement, where the molecules are collectively aligned perpendicularly to the channels' long axes, does not originate in any pre-alignment effects in the nanoconfined liquid due to capillary nematization.
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