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

空气/水界面处对齐层状相和单层上的抗衡离子分布

• 批准号: 5415793
• 负责人: Professor Dr. Tim Salditt
• 金额: --
• 依托单位: Institut für Theoretische Physik
• 依托单位国家: 德国
• 项目类别: Research Grants
• 财政年份: 2004
• 资助国家: 德国
• 起止时间: 2003-12-31 至 2008-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/5415793?language=en
• 关键词: Counterion; Distribution; Aligned; Lamellar; Phases

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.

我们提出了一个调查的counterweight分布和相关的相互作用，在带电的层状相组成的（i）带电磷脂和（ii）带电的表面活性剂系统。在这些相中，相互作用力和波动与中性或两性离子对应物有着根本的不同，通常会导致新的自组装结构和中间相[Zemb et al 1999，Rädler et al. 1996，Koltover et al. 1998，Salditt et al 1997]。反离子分布rCs（z）是特别感兴趣的，不仅对于相图和层状相的相互作用，而且在许多胶体和生物分子系统中也是如此，并且应该通过异常散射技术（用溴化物、铯、铷代替反离子）来确定。以前对带电和软界面（如膜）附近的电荷分布的研究仅限于各向同性本体悬浮液（SAXS），并且分辨率较弱[Richardson等人，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。我们的目标是在rCs（z）的分辨率是足够高的观察可能的偏差从泊松-玻尔兹曼近似。静电力和界面波动之间微妙的相互作用应予以阐明。由于它已被证明，counterweight的大小有一个显着的影响，在空气-水界面处的高度负电荷的单分子膜的表面电位，二维单分子膜将被研究的表面电位测量，掠入射X射线衍射，X射线反射率和红外反射吸收光谱。我们计划研究单价（碱金属）以及二价（碱土金属）阳离子与不同大小的依赖于单分子层的电荷密度之间的竞争。红外光谱将用于测量不同的抗衡离子对羧酸的电离行为的影响，这取决于界面和亚相之间的pH间隙，因此对双电层（EDL）电位。这些结果将与三维系统（高度对齐的多层系统和胶束）中获得的结果进行比较。实验结果的基础上，一个新的理论描述的EDL的发展。