Continuous Polyelectrolyte Adsorption under an Applied Electric Potential

Van Tassel / Yale U.（0651980）通过多电解质吸附形成的纳米级薄膜在分离膜、生物和化学传感底物以及细胞接触生物材料方面有着重要的应用。衬底电位是一个重要的控制变量,并在研究的影响,研究人员最近发现了一个有趣的现象:某些聚阳离子的吸附可能变得连续,即渐近线性(或近线性)/小时,在适度的阳极的应用潜力。在以前未观察到的外加电位下的连续吸附，提供了令人兴奋的技术可能性，同时提出了一些基本问题：在什么系统和什么条件下会发生连续吸附？． 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的初步工作已经确定了连续吸附发生的系统和条件。为了了解薄膜性质对形成条件的依赖性，从而最终设计出电势控制下的聚电解质薄膜，以用于重要应用，PI将进行实验和计算研究，以了解在应用电位下连续吸附聚电解质的机理。具体而言，该项目采用原子力显微镜（AFM）、光波导光模光谱（owl）、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理解这些发现。更广泛的影响：人们可以设想在应用电位下连续的聚电解质吸附在包括传感、催化和生物电子学在内的几个技术领域产生广泛的影响。许多应用需要精确厚度和组成的聚电解质纳米膜，并且连续吸附容易地允许膜生长到任何所需的水平，在一个步骤和单一聚合物组分中。相比之下，标准的单层吸附仅限于相当薄的层，而逐层组装（可能有更厚的层）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。Pis推测连续吸附会导致一个非常密集的区域，具有狭窄的孔径分布，靠近底物，原则上是理想的分离。薄膜的单组分特性可以使离子导电膜变得更好，因为（不像一层一层的薄膜）聚合物的所有带电位点都可以与移动离子协调。这个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针对上述目标进行实验和计算工作。本科生将至少包括一名来自耶鲁大学STARS项目的学生，该项目支持少数族裔和女性学生。进一步的影响将来自对纽黑文一所公立高中的推广努力。Pis为一名参加耶鲁学者计划的当地高中生提出了一个实验室体验，包括多电解质吸附实验，一个包括课堂和实验室的住宿体验。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.