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

我们建议对由（i）带电磷脂和（ii）带电表面活性剂系统组成的带电层状相中的反离子分布和相关相互作用进行研究。这些相中的相互作用力和波动与中性或两性离子对应物有根本不同，通常会导致新颖的自组装结构和中间相[Zemb et al 1999, Rädler et al. 2017]。 1996，科尔托弗等人。 1998 年，Salditt 等人 1997 年]。反离子分布 rCs(z) 特别令人感兴趣，不仅对于相图和层状相中的相互作用，而且对于许多胶体和生物分子系统也是如此，并且应通过反常散射技术（用溴化物、铯、铷替代反离子）来确定。先前对带电界面和软界面（例如膜）附近反离子分布的研究仅限于各向同性本体悬浮液 (SAXS)，并且分辨率较低 [Richardson et al 1996]。本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 rCs(z) 的分辨率足够高，以观察与泊松-玻尔兹曼近似的可能偏差。应阐明静电力和界面波动之间的微妙相互作用。由于已证明抗衡离子尺寸对空气-水界面处带高负电荷的单层膜的表面电势有显着影响，因此将通过表面电势测量、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膜。我们计划研究不同尺寸的单价（碱金属）和二价（碱土金属）阳离子之间的竞争，取决于单层的电荷密度。红外光谱将用于测量不同抗衡离子对羧酸电离行为的影响，这取决于界面和面下相之间的 pH 差距，因此也取决于双电层 (EDL) 电势。这些结果将与三维系统（高度排列的多层系统和胶束）中获得的结果进行比较。在实验结果的基础上，预计会发展出新的 EDL 理论描述。

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.