Macro-Ions Near Confining Surfaces: Influence on Colloidal Forces

货车塔塞尔，保罗R.耶鲁大学“宏观离子附近的限制表面：对胶体力的影响“胶体力之间的超纳米大小的物体在电解质溶液中管理许多工业和医学上的重要系统。双电层、货车德瓦尔斯和耗尽相互作用对整个胶体力有重要贡献。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质，但小于胶体物体。净力是由两个较大物体之间接触附近区域的不平衡渗透压产生的，这是由于该区域中添加的组分的浓度和结构发生改变。目前对耗尽力的理解主要基于与球形添加剂的空间（即硬颗粒）相互作用。然而，使用带电和/或非球形大分子添加剂可能产生更显著的效果;如果要实现胶体/蛋白质结晶、分离和生物测定中的重要应用，则必须理解/控制这一点。该项目提出了一个理论和实验相结合的努力，以理解，预测和技术开发的影响，大分子添加剂的电荷和形状对胶体力。该系统的研究包括一个球形，约。10微米的胶体颗粒附近的一个光滑的平面上存在的大离子（约。10 nm球形或棒状胶体颗粒）和微离子（原子大小的抗衡离子/盐）。重点是宏观离子组分在颗粒与表面之间的差距中的行为及其与胶体力的关系。PI带来承担国家的最先进的实验和现代分子理论的宏观离子在一个有限的几何形状的研究。第一个目标是在宏观离子的存在下，模型胶体颗粒（聚苯乙烯或二氧化硅）和平面表面（二氧化硅）之间的力与距离分布的实验理解。PI将采用全内反射显微镜（TIRM）和原子力显微镜（AFM），其意义将是系统地考虑宏观离子电荷、尺寸/形状和浓度-以及微观离子电荷和浓度-对胶体力与距离分布的影响。第二个目标是实验研究的系统的分子结构和力分布的理论预测。PI将采用Monte Carlo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-以及通过实验研究不容易寻址的系统的可能性-从而导致理解相互作用的胶体系统的真正预测框架。第三个目标是利用这种预测框架来开发宏离子添加剂的两种新应用。一种是用于颗粒分离的基于色谱的工具，另一种是用于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，PI建议本科生积极参与研究活动。PI建议通过为耶鲁大学本科实验室课程开发适当的AFM实验，进一步将这项研究融入我们的本科课程。支持本科生的资金将通过NSF REU计划进行。由于所提出的方法（如AFM）在研究界越来越受欢迎，他们预计学生的经验将作为后续研究生学习的良好准备。学习这些方法的研究生将进行一个教程，然后学生将有机会使用这些方法测量表面力。PI预计学生开始参与粒子和平面之间的力作为添加盐的函数，然后移动到简单的宏观离子添加剂（如二氧化硅），在那里发生力振荡。其意义将是早期接触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.