Continuous Polyelectrolyte Adsorption under an Applied Electric Potential

货车塔塞尔/耶鲁大学通过纳米吸附形成的纳米级薄膜发现了作为分离膜、生物和化学传感基底以及细胞接触生物材料的重要应用。底物电势是一个重要的控制变量，在研究其影响时，研究人员最近发现了一个有趣的发现：某些聚阳离子的吸附可能会变得连续，即在适当的阳极电势下，随着时间的推移呈渐近线性（或接近线性）。在施加的电势下连续吸附，以前没有观察到，提供了令人兴奋的技术可能性，同时提出了基本问题：。对于什么系统，在什么条件下，会发生连续吸附？.通过连续吸附形成的膜的物理化学性质如何取决于控制变量（电压、pH、盐、分子量）？.连续吸附的机理是什么？PI的初步工作确定了发生连续吸附的系统和条件。为了了解薄膜性能对形成条件的依赖性，从而最终在重要应用的电势控制下设计薄膜，PI将进行实验和计算研究，以了解在施加电势下连续吸附的机理。具体而言，该项目采用原子力显微镜（AFM）、光波导光模光谱（OWLS）、X射线光电子能谱（XPS）和分子模拟来确定聚合物层结构、电荷和电化学状态的演变，并从分子水平事件的角度来理解这些发现。人们可以设想在施加的电势下连续的吸附在包括传感、催化和生物电子学在内的几个技术领域中具有广泛的影响。许多应用需要精确厚度和组成的纳米薄膜，并且连续吸附容易地允许薄膜在单个步骤中并且使用单个聚合物组分生长到任何期望的水平。相比之下，标准单层吸附限于相当薄的层，并且逐层组装（其中较厚的层是可能的）需要许多步骤和至少两个组件。某些独特的聚合物层特性也是可能的。PI推测连续吸附导致非常致密的区域，具有窄的孔径分布，靠近基材，原则上是分离的理想选择。该膜的单组分性质可以使上级离子传导膜成为可能，因为（与逐层膜不同）聚合物的所有带电位点都可用于与移动的离子配位。该项目带来的教育经验也将产生广泛的影响。两名全日制博士生将对国家目标进行实验和计算工作。本科生的参与将包括至少一名来自耶鲁大学STARS项目的学生，该项目支持少数民族和女性学生。对纽黑文一所公立高中的外联工作将产生进一步的影响。Pis提出了一个实验室的经验，涉及吸附实验，为当地高中学生参加在耶鲁大学的学者计划，包括课堂和实验室产品的住宅体验。最后，该项目建议开发一个关于聚合物涂层的课程模块，包括一系列讲座和实验，作为胶体和材料科学现有本科和研究生课程的一部分。

Van Tassel / Yale U. (0651980)Nanoscale thin films formed via polyelectrolyte adsorption find important applications as separation membranes, bio- and chemical sensing substrates, and cell-contacting biomaterials. Substrate electric potential is an important control variable, and while studying it influence, the investigators recently made an interesting discovery: the adsorption of certain polycations may become continuous, i.e. asymptotically linear (or nearly linear) in time over hours, upon the application of a modest anodic potential. Continuous adsorption under an applied electric potential, not previously observed, offers exciting technological possibilities while raising fundamental questions: . For what systems, and under what conditions, does continuous adsorption occur? . How do the physico-chemical properties of films formed by continuous adsorption depend on the control variables (voltage, pH, salt, molecular weight)? . What is the mechanism of continuous adsorption?Preliminary work by the PI has identified systems and conditions where continuous adsorption occurs. In order to understand the dependence of film properties on formation conditions, and thus ultimately to engineer polyelectrolyte films under electric potential control for important applications, the PI will conduct an experimental and computational study toward a mechanistic understanding of continuous polyelectrolyte adsorption under an applied potential. Specifically, the project employs atomic force microscopy (AFM), optical waveguide lightmode spectroscopy (OWLS), X-ray photoelectron spectroscopy (XPS), and molecular simulation to determine the evolution of polymer layer structure, charge, and electrochemical state and to understand these findings in terms ofmolecular-level events.Broader Impact: One may envision continuous polyelectrolyte adsorption under an applied electric potential to have a broad impact in several areas of technology including sensing, catalysis, and bioelectronics. Many applications require polyelectrolyte nanofilms of precision thickness and composition, and continuous adsorption easily allows for film growth to any desired level, in a single step and with a single polymer component. In contrast, standard monolayer adsorption is limited to rather thin layers, and layer-by-layer assembly (where thicker layers are possible) requires many steps and at least two components. Certain unique polymer layer characteristics may also be possible. The Pis speculate continuous adsorption to result in a very dense region, with a narrow pore size distribution, near to the substrate, in principle ideal for separations. The single component nature of the films could enable superior ionic conducting membranes, since (unlike layer-by-layer films) all of the polymer's charged sites would be available to coordinate with mobile ions. The educational experiences brought forth by this project will also have a broad impact. Two full-time PhD students will conduct experimental and computational work toward the statedobjectives. Undergraduate participation will include at least one student from the STARS program at Yale, which supports minority and female students. Further impact will result from an outreach effort to a New Haven public high school. The Pis propose a laboratory experience, involving polyelectrolyte adsorption experiments, for a local high school student participating in the SCHOLAR program at Yale, a residential experience including classroom and laboratory offerings. Finally, the project proposes to develop a course module on polymer coatings, consisting of a series of lectures and experiments, to be included as part of existing undergraduate and graduate courses in colloids and materials science.