Jagiellonian University, Faculty of Chemistry, R. Ingardena 3, 30-060 Kraków, Poland.
J Colloid Interface Sci. 2010 Jun 1;346(1):153-62. doi: 10.1016/j.jcis.2010.02.045. Epub 2010 Feb 23.
A series of semifluorinated thiols of the general formula CF(3)(CF(2))(m-1)(CH(2))(n)SH (abbreviated to FmHnSH) have been synthesized and the Langmuir monolayers thoroughly characterized using surface pressure (π) and electric surface potential (ΔV) measurements. These data have been complemented with Brewster angle microscopy (BAM) visualization of the monolayers structure and IR spectroscopy (PM-IRRAS) analysis of the alkyl chain conformation. The investigated thiols (namely F4H10SH, F8H6SH, F6H10SH, F10H6SH, F6H11SH, F8H10SH and F10H10SH) differ in the length of the hydrophobic chain as well as in the degree of fluorination. Although the -SH group cannot form strong hydrogen bonds with the water subphase, thereby causing only weak anchoring, it has been found that all the investigated thiols, except for F4H10SH, are capable of stable Langmuir monolayer formation. The investigated thiols can be divided into two categories - thiols with longer alkyl chain (F10H10SH, F10H6SH, F8H10SH) and compounds with shorter hydrophobic part (F6H10SH, F6H11SH, F8H6SH). The monolayers of the latter thiols have their equilibrium surface pressure (ESP) comparable with the collapse pressure (π(C)) of their monolayers; thus these films are stable within the whole range of compression. On the contrary, thiols with longer perfluorinated fragments have considerably lower ESP than the π(C) of their monolayers; therefore, both stable and metastable regions can be distinguished in their π-A isotherms. Interestingly, for F8H6SH, a smectic ordering of molecules can be observed in monolayers as visualized with BAM. By comparing film-forming properties of the studied semifluorinated thiols with previously studied semifluorinated alkanes it has been found that the presence of -SH group facilitates spreading at the free water surface. Semifluorinated thiols have been found to maintain their monomolecular ordering in the presence of heavy metal cations in the aqueous subphase, contrary to their hydrogenated analogues, which have been reported to crystallize under the same conditions.
一系列通式为 CF(3)(CF(2))(m-1)(CH(2))(n)SH（简写为 FmHnSH）的半氟化硫醇已被合成，并通过表面压力（π）和电动表面电势（ΔV）测量对其进行了充分的Langmuir 单层膜特性研究。这些数据与单层膜结构的布鲁斯特角显微镜（BAM）可视化和烷基链构象的红外光谱（PM-IRRAS）分析进行了补充。所研究的硫醇（即 F4H10SH、F8H6SH、F6H10SH、F10H6SH、F6H11SH、F8H10SH 和 F10H10SH）在疏水性链的长度以及氟化程度上有所不同。尽管-SH 基团不能与水亚相形成强氢键，从而导致只有弱的固定，但是已经发现，除了 F4H10SH 之外，所有研究的硫醇都能够稳定地形成 Langmuir 单层膜。所研究的硫醇可以分为两类 - 具有较长烷基链的硫醇（F10H10SH、F10H6SH、F8H10SH）和具有较短疏水性部分的化合物（F6H10SH、F6H11SH、F8H6SH）。后者的硫醇的单层膜的平衡表面压力（ESP）与它们的单层膜的崩溃压力（π(C)）相当；因此，这些薄膜在整个压缩范围内都是稳定的。相反，具有较长全氟片段的硫醇的 ESP 明显低于它们的单层膜的 π(C)；因此，它们的 π-A 等温线可以区分稳定和亚稳区域。有趣的是，对于 F8H6SH，可以观察到 BAM 可视化的分子层状有序。通过将研究的半氟化硫醇的成膜性能与之前研究的半氟化烷烃进行比较，发现-SH 基团的存在有利于在自由水表面的铺展。与它们的氢化类似物相反，半氟化硫醇在水亚相中存在重金属阳离子时能够保持其单分子有序性，因为后者在相同条件下已经被报道结晶。
