Dupont Audrey, Eastoe Julian, Murray Martin, Martin Laura, Guittard Frederic, Taffin de Givenchy Elisabeth, Heenan Richard K
School of Chemistry, University of Bristol, Bristol, BS8 1TS United Kingdom.
Langmuir. 2004 Nov 9;20(23):9953-9. doi: 10.1021/la048447z.
Six different hybrid fluorocarbon-hydrocarbon (F-H) sulfate and sulfonate surfactants, with variations in the relative F/H carbon chain length, have been synthesized and characterized in aqueous solution. These compounds have been targeted for potential activity in densified CO2. Tensiometric data and chemical analyses were consistent with surfactants of high chemical purity. Fluorination in terms of the F/H ratio exerts a strong control over all the surfactant physicochemical properties, including critical micelle concentrations (cmc's) and adsorption isotherms. One of these partially fluorinated surfactants (the sulfonate phi-F6H4) achieves very low surface tensions in water (gamma(cmc) approximately 19 mN m(-1)) more reminiscent of fully fluorinated double-chain compounds. Detailed 19F NMR studies revealed that omega'-CF3 groups can exhibit separate signals for monomeric and micellized forms, hence facilitating cmc determinations. Small-angle neutron scattering investigations confirmed the presence of ellipsoidal or extended disklike micelles, depending on the F-H chain asymmetry. For example, a symmetric hybrid F8H8 generates disklike micelles, whereas chain asymmetry in F8H4 or phi-F6H4 tends to drive cylindrical aggregation structures. These changes are consistent with variations in the surfactant packing parameter caused by the different chain F/H ratios. Hence, adsorption and aggregation are shown to respond in a predictable way to the molecular structure of these unusual surfactants.
已合成了六种不同的氟碳 - 烃（F - H）硫酸盐和磺酸盐表面活性剂，它们的相对F/H碳链长度有所不同，并在水溶液中进行了表征。这些化合物被目标用于致密二氧化碳中的潜在活性。表面张力数据和化学分析与高化学纯度的表面活性剂一致。就F/H比而言，氟化对所有表面活性剂的物理化学性质都有很强的控制作用，包括临界胶束浓度（cmc）和吸附等温线。其中一种部分氟化的表面活性剂（磺酸盐phi - F6H4）在水中能达到非常低的表面张力（γ(cmc)约为19 mN m(-1)），更类似于全氟化双链化合物。详细的19F NMR研究表明，ω'-CF3基团对于单体和胶束化形式可呈现出单独的信号，因此便于确定cmc。小角中子散射研究证实了椭圆形或延伸盘状胶束的存在，这取决于F - H链的不对称性。例如，对称的混合F8H8产生盘状胶束，而F8H4或phi - F6H4中的链不对称性倾向于驱动形成圆柱形聚集结构。这些变化与由不同链F/H比引起的表面活性剂堆积参数的变化一致。因此，吸附和聚集对这些特殊表面活性剂的分子结构以可预测的方式做出响应。
