Macro-Ions Near Confining Surfaces: Influence on Colloidal Forces

范塔塞尔，保罗·R·耶鲁大学“限制表面附近的宏观离子：对胶体力的影响”超纳米尺寸物体之间的胶体力在电解质溶液中支配着许多工业和医学上的重要系统。双电层、范德华和耗尽相互作用对整个胶体力的贡献很大。后者是由添加的大分子组分引起的，其尺寸大于溶剂和电解液，但小于胶体物体。净力来自两个较大物体接触附近区域的不平衡渗透压力，这是由于该区域附加成分的浓度和结构发生了变化。目前对耗尽力的理解主要是基于空间(即硬粒子)与球形添加剂的相互作用。然而，使用带电和/或非球形的大分子添加剂可能产生更显著的效果；如果要在胶体/蛋白质结晶、分离和生物测定中实现重要的应用，必须理解/控制这一点。该项目提出了一项理论和实验相结合的努力，以了解、预测和技术开发大分子添加剂电荷和形状对胶体力的影响。研究体系包括一个球形的、约10微米的胶体颗粒，靠近光滑的平坦表面，在宏观离子(约10 nm球形或棒状胶体颗粒)和微离子(原子大小的反离子/盐)存在下。重点放在颗粒和表面间隙中的宏观离子成分的行为及其与胶体力的关系上。PI将最先进的实验和现代分子理论应用于这一受限几何中的宏观离子的研究。第一个目标是在实验上了解模型胶体粒子(聚苯乙烯或二氧化硅)和平面(二氧化硅)之间的力与距离的关系。PI将使用全内反射显微镜(TIRM)和原子力显微镜(AFM)，其意义将是系统地说明宏观离子电荷、大小/形状和浓度-以及微观离子电荷和浓度-对胶体力随距离分布的影响。第二个目标是对实验研究的体系的分子结构和力分布进行理论预测。PI将使用蒙特卡罗模拟和密度泛函理论，其意义将是对我们的实验结果的分子理解/解释-以及研究无法通过实验解决的系统的可能性-从而产生一个真正的预测框架来理解相互作用的胶体系统。第三个目标是利用这一预测框架开发大离子添加剂的两个新应用。一种是基于层析的颗粒分离工具，另一种是提高生物分析工具的有效性的方法，例如细胞分离或微生物检测。其意义可能是利用宏观离子控制胶体力的新技术。更广泛的社会影响：为了扩大科学目标的影响，PIs建议本科生积极参与研究活动。PIS建议通过为耶鲁大学本科生实验室课程开发适当的AFM实验，将这项研究进一步整合到我们的本科课程中。用于支持本科生的资金将通过NSF REU计划进行。由于拟议的方法(如原子力显微镜)在研究界越来越受欢迎，他们预计学生的体验将为后续的研究生学习做好准备。接受这些方法培训的研究生将进行辅导，然后学生将有机会使用这些方法测量表面力。PI预期学生开始参与时，粒子和平面之间的力作为添加盐的函数，然后转移到发生力振荡的简单宏观离子添加剂(如二氧化硅)。重要的是及早接触到最先进的表面分析方法。

Van Tassel, Paul R.Yale University"Macro-Ions Near Confining Surfaces: Influence on Colloidal Forces"Colloidal forces between supra-nanometer sized objects in electrolyte solutions govern many industrially and medically important systems. Significant contributions to the overall colloidal force arise from electric double layer, van der Waals, and depletion interactions. The latter is brought about by an added macromolecular component whose size is larger than the solvent and electrolyte but smaller than the colloidal objects. A net force results from the unbalanced osmotic pressure in the region near contact between two larger objects due to the altered concentration and structure of the added component in this region. Current understanding of the depletion force is based primarily on steric (i.e. hard particle) interactions with spherical additives. However, a much more pronounced effect is possible using charged and/or non-spherical macromolecular additives; this must be understood/controlled if important applications in colloid/protein crystallization, separation, and bioassay are to be realized. This project proposes a combined theoretical and experimental effort toward understanding, predicting, and technologically exploiting the influence of macromolecular additive charge and shape on colloidal force. The system of study consists of a spherical, ca. 10 micron colloidal particle near a smooth flat surface in the presence of macro-ions (ca. 10 nm spherical or rod-like colloidal particles) and micro-ions (atomic-sized counter ions/salt). The focus is on the behavior of the macro-ion component in the gap between the particle and the surface and its relation to colloidal force. The PIs bring to bear state-of-the-art experiment and modern molecular theory to this study of macro-ions in a confined geometry. The first objective is the experimental understanding of the force versus distance profile between a model colloidal particle (polystyrene or silica) and a planar surface (silica) in the presence of macro-ions. The PIs will employ total internal reflection microscopy (TIRM) and atomic force microscopy (AFM) and the significance will be a systematic account of the influence of macro-ion charge, size/shape, and concentration - and micro-ion charge and concentration - on the colloidal force versus distance profile. The second objective is the theoretical prediction of the molecular structure and force profiles of the systems investigated experimentally. The PIs will employ Monte Carlo simulation and density functional theory and the significance will be a molecular understanding/interpretation of our experimental results - and the possibility of investigating systems not readily addressable via experiment - thus leading to a true predictive framework for understanding interacting colloidal systems. The third objective is to exploit this predictive framework to develop two novel applications of macro-ion additives. One is a chromatography-based tool for particle separation and the other a method for improving the effectiveness of bio-analytical tools in, e.g., cell separation or microorganism detection. The significance could be new technologies exploiting macro-ion control of colloidal forces. Broader Social Impact: To broaden the impact of the scientific objectives, the PIs propose the active participation of undergraduate students in the research activities. The PIs propose to further integrate this research into our undergraduate curriculum by developing an appropriate AFM experiment for the Yale undergraduate lab course. Funds for supporting the undergraduate student will be pursued through the NSF REU program. Because the proposed methods (like AFM) are growing in popularity within the research community, they anticipate the student experience will serve as an excellent preparation for subsequent graduate study. Graduate students schooled in these methods will conduct a tutorial, and students will then have an opportunity to measure surface forces using these methods. The PIs anticipate beginning student participation with the force between a particle and a flat surface as a function of added salt and then moving to simple macro-ion additives (like silica) where force oscillations occur. The significance will be an early exposure to state-of-the-art surface analytical methods.