Moilanen David E, Fenn Emily E, Wong Daryl, Fayer M D
Department of Chemistry, Stanford University, Stanford, California 94305, USA.
J Am Chem Soc. 2009 Jun 17;131(23):8318-28. doi: 10.1021/ja901950b.
To determine the relative importance of the confining geometry and nanoscopic length scale versus water/interface interactions, the dynamic interactions between water and interfaces are studied with ultrafast infrared spectroscopy. Aerosol OT (AOT) is a surfactant that can form two-dimensional lamellar structures with known water layer thickness as well as well-defined monodispersed spherical reverse micelles of known water nanopool diameter. Lamellar structures and reverse micelles are compared based on two criteria: surface-to-surface dimensions to study the effect of confining length scales, and water-to-surfactant ratio to study water/interface interactions. We show that the water-to-surfactant ratio is the dominant factor governing the nature of water interacting with an interface, not the characteristic nanoscopic distance. The detailed structure of the interface and the specific interactions between water and the interface also play a critical role in the fraction of water molecules influenced by the surface. A two-component model in which water is separated into bulk-like water in the center of the lamellar structure or reverse micelle and interfacial water is used to quantitatively extract the interfacial dynamics. A greater number of perturbed water molecules are present in the lamellar structures as compared to the reverse micelles due to the larger surface area per AOT molecule and the greater penetration of water molecules past the sulfonate head groups in the lamellar structures.
为了确定限制几何形状和纳米尺度相对于水/界面相互作用的相对重要性，利用超快红外光谱研究了水与界面之间的动态相互作用。气溶胶OT（AOT）是一种表面活性剂，它可以形成具有已知水层厚度的二维层状结构以及具有已知水纳米池直径的明确单分散球形反胶束。基于两个标准对层状结构和反胶束进行比较：表面到表面的尺寸以研究限制长度尺度的影响，以及水与表面活性剂的比例以研究水/界面相互作用。我们表明，水与表面活性剂的比例是控制与界面相互作用的水的性质的主导因素，而不是特征纳米距离。界面的详细结构以及水与界面之间的特定相互作用在受表面影响的水分子比例中也起着关键作用。使用一种双组分模型，其中水被分为层状结构或反胶束中心的类似本体的水和界面水，以定量提取界面动力学。与反胶束相比，层状结构中存在更多受扰动的水分子，这是由于每个AOT分子的表面积更大，以及水分子在层状结构中穿过磺酸根基团的渗透能力更强。
