Materials World Network: Polyelectrolyte Brushes: Understanding Multi-Valent Effects on Structure and Properties

这一由加州大学圣巴巴拉分校和德国拜罗伊特大学合作的综合性项目旨在加深理解并揭示多价离子介质中的聚电解质刷体系中的新现象，该多价离子介质中含有金属离子、带电表面活性剂、分子离子、蛋白质和带相反电荷的聚电解质。最近通过表面力测量进行的初步工作表明，相对于单价盐，聚电解质刷子在多价介质中具有新的行为。表面力装置已经被用来演示在好的溶剂中浸泡的刷子和刷子之间施加的扩展构型和长程力。特别是，在一些多价介质中存在强烈的崩塌转变，在平坦和高度弯曲的表面上都可以观察到。新的行为标志着聚电解质刷子在一系列重要应用中具有新的性能。多价离子介质中的聚电解质表面性质，如生理环境、医疗器械表面、水基悬浮液的流变性、聚电解质的絮凝或凝结，或在使用许多个人护理产品的硬家用水和表面活性剂混合物中，可能不能从构成我们当前知识基础的单价盐实验中直接推断出来。由带电的大分子组成的软界面在生物学中是正常的，如细胞糖萼、肺组织、眼皮和关节软骨的表面，以及骨骼中矿化的胶原纤维之间的界面。商业产品，如个人护理(如洗发水、护肤品)、医疗假体(如关节置换)、材料加工(如悬浮颗粒或组件的空间稳定化分散体)、防雾表面和基因芯片，也经常依赖于高度水合的带电聚合物界面。这项工作的结果有望在生物和医药、水净化、水性颜料、涂料和化妆品工业中得到应用。由于加州大学圣巴巴拉分校(UCSB)和贝罗伊特大学(UB)之间的合作，这项拟议的工作将使人们能够清楚地看到，在平面上捆绑的聚电解质实验(在UCSB)是如何与分散胶体表面常见的高度弯曲的刷子(在UB)连接的。在这两个系统中，聚合物和离子限制的物理原理是相同的。上面提到的许多实际情况可能涉及多价离子，与只包含单价离子的介质相比，多价离子的实验信息和已建立的理论原理要少得多。例如，生物缓冲液通常含有许多离子物种，包括多价离子。已知的多价相互作用对溶液中的聚电解质有很强的影响，例如在DNA的缩合中，尽管许多研究是在自由溶液中进行的，并且荷电界面具有广泛的生物学和技术意义，但对于它们对界面系留聚电解质的影响研究很少。系留组件中的聚合物链(表面刷子、系在颗粒上的链和高度支化的大分子)提供了一种对大分子系结端的实验性“抓地力”，这使得能够以一种无法用溶液中的游离线性聚合物完成的方式来直接测量力。

This comprehensive program between the University of California at Santa Barbara and the Universitt Bayreuth in Germany aims at deepening understanding and uncovering new phenomena in systems of polyelectrolyte brushes immersed in multi-valent ionic media containing metal ions, charged surfactants, molecular ions, proteins and oppositely charged polyelectrolytes. Recent preliminary work via surface force measurement has shown new behavior, relative to that in mono-valent salt, of polyelectrolyte brushes in multi-valent media. The Surface Forces Apparatus has been used to demonstrate the extended configurations and long-range forces exerted by and between brushes immersed in good solvents. In particular, there are strong collapse transitions in some multi-valent media, observable of both flat and highly curved surfaces. New behavior signals new properties in a range of important applications of polyelectrolyte brushes. Polyelectrolyte surface properties in multi-valent ionic media, such as in physiological environments, surfaces of medical devices, rheology of water-based suspensions, flocculation or condensation of polyelectrolytes, or in the hard household water and surfactant mixtures in which many personal care products are employed, may not be straightforwardly inferred from experiments in mono-valent salt, which constitute our current knowledge base. Soft interfaces that consist of charged macromolecules, highly swollen with water, are the norm in biology, such as the cellular glycocalyx, the surfaces of lung tissue, eyelids and articular cartilage, and the interfaces between mineralized collagen fibrils in bone. Commercial products, such as those for personal care (e.g., shampoo, skin care), medical prostheses (e.g., joint replacements), materials processing (e.g., sterically stabilized dispersions of suspended particles or assemblies), anti-fogging surfaces, and gene chips, also often rely on highly hydrated, charged polymer interfaces.The results of this work are anticipated to have applications in biology and medicine, water purification, water-based pigments, paints and coatings and the cosmetic product industry. By virtue of the collaboration between UC Santa Barbara (UCSB) and the Universitt Bayreuth (UB) that this proposed work will enable, a clear picture will emerge of how experiments on polyelectrolytes tethered to flat surfaces (at UCSB) connect with highly curved brushes (at UB), common to the surfaces of dispersed colloids. The same physics of polymers and ion confinement is at play in both systems. Many of the practical situations cited above can involve multi-valent ions for which there is much less experimental information and fewer established theoretical principles, than for media comprising mono-valent ions exclusively. Biological buffers, for example, typically contain many ionic species, including multi-valents. Multi-valent interactions, known to have strong effects on polyelectrolytes in solution, as in the condensation of DNA, have been studied very little in their effects on interfacially tethered polyelectrolytes, despite many studies in free solution and the broad biological and technological significance charged interfaces. Polymer chains in tethered assemblies (surface brushes, chains tethered to particles, and highly branched macromolecules) provide an experimental "grip" on the tethered ends of the macromolecules, which enables direct measurement of forces in a way that cannot be done with free linear polymers in solution.