Counterion Distribution in Aligned Lamellar Phases and on Monolayers at the air/water Interface

我们建议研究由(i)带电荷磷脂和（ii）带电荷表面活性剂系统组成的带电荷层状相中的反离子分布和相关的相互作用。这些相中的相互作用力和波动与中性或两性离子相根本不同，往往导致新的自组装结构和中间相[Zemb等人1999年，Rädler等人1996年，Koltover等人1998年，Salditt等人1997年]。反离子分布rc (z)不仅对相图和层状相的相互作用，而且对许多胶体和生物分子系统也具有特别的意义，并且应该通过反常散射技术（溴离子，铯，铷取代反离子）来确定。以前对带电界面和软界面（如膜）附近的反离子分布的研究仅限于各向同性体悬浮液（SAXS），并且分辨率很低[Richardson等，1996]。目前的方法是使用适合界面敏感衍射技术的高度定向系统。我们的目标是rc (z)的分辨率足够高，可以观察到泊松-玻尔兹曼近似的可能偏差。静电力和界面波动之间微妙的相互作用应加以阐明。由于已经证明了反离子大小对空气-水界面处高负电荷单层的表面电位有显著影响，因此将通过表面电位测量、掠入射x射线衍射、x射线反射率和红外反射吸收光谱来研究二维单层。我们计划研究不同尺寸的一价（碱金属）和二价（碱土金属）阳离子之间的竞争，这取决于单层的电荷密度。红外光谱将用于测量不同反离子对羧酸电离行为的影响，这取决于界面和亚相之间的pH间隙，因此取决于双电层（EDL）电位。这些结果将与在三维系统（高度排列的多层系统和胶束）中得到的结果进行比较。在实验结果的基础上，展望了新的理论描述的发展。

We propose an investigation of the counterion distribution and the associated interactions in charged lamellar phases composed of (i) charged phospholipids and (ii) charged surfactant systems. Interaction forces and fluctuations are fundamentally different in such phases from the neutral or zwitterionic counterparts, often leading to novel self-assembled structures and mesophases [Zemb et al 1999, Rädler et al. 1996, Koltover et al. 1998, Salditt et al 1997]. The counterion distribution rCs(z) is of particular interest, not only for the phase diagram and the interactions in lamellar phases but in many colloidal and biomolecular systems as well, and shall be determined from anomalous scattering techniques (counterion replacement by Bromide, Caesium, Rubidium). Previous studies of the counterion distribution near charged and soft interfaces such as membranes have been restricted to isotropic bulk suspensions (SAXS) and have suffered from weak resolution [Richardson et al 1996]. The present approach is to use highly oriented systems amenable to interface-sensitive diffraction techniques. We aim for a resolution in rCs(z) which is high enough to observe possible deviations from the Poisson-Boltzmann approximation. The subtle interplay between electrostatic forces and interface fluctuations shall be elucidated. Since it has been demonstrated that the counterion size has a pronounced effect on surface potential for highly negatively charged monolayers at the air-water interface, two-dimensional monolayers will be studied by surface potential measurements, grazing incidence x-ray diffraction, x-ray reflectivity and IR reflection-absorption spectroscopy. We plan to study the competition between univalent (alkali metals) as well as divalent (alkali-earth metals) cations with different size in dependence on the charge density of the monolayer. Infrared spectroscopy will be used to measure the effect of different counterions on the ionization behavior of carboxylic acids, which depends on the pH gap between the interface and the subphase and therefore on electrical double layer (EDL) potential. These results will be compared with results obtained in three-dimensional systems (highly aligned multilamellar systems and micelles). On the basis of the experimental results, a development of new theoretical descriptions of EDL is expected.