Polyelectrolyte brushes: Stabilization through Controlled Charge Placement

在这个由化学系大分子、超分子和纳米化学项目资助的项目中，克里斯托弗·K·康奈尔大学的奥伯正在开发和研究具有受控充电位置的电刷。 聚合物刷是一种特殊的大分子结构，聚合物链密集地拴在表面上。 它们具有独特和有用的性质，包括蠕虫状构象，紧凑的分子尺寸，以及由于其紧凑和受限的结构而引起的显著的聚合物链端效应。 这些特殊的生物刷可以根据生命系统的性质主动或被动地与生物环境相互作用。 因此，刷子是生物医学设备，化学传感器和药物输送系统的有前途的材料。 在这项研究中，合成方法被选择来构建带电刷，允许系统的调查如何电荷的位置改变的膨胀，形状，流动性和稳定性的合成刷。 使用复杂的化学测量技术进行表征，还包括溶液酸度和金属离子对电刷行为的影响。 这项研究是跨学科的性质，包括与德国和英国的研究人员的国际合作。 该研究计划使研究生和相关研究人员接触到国际科学观点。 研究生作为导师和榜样，本科生，而在同一时间gaini监督技能。 康奈尔大学的本科生在学年期间参加研究，而其他学校的学生则在夏季参加研究，重点是代表性不足的社区。 外联活动包括通过举办讲习班向高中学生和教师提供服务。 本研究的重点是一系列模型聚（电解质）（PEL）刷的制备和研究与精心定制的放置的阳离子和阴离子基团单独或组合使用在一个单一的链和瓶刷架构的基础上丙烯酰胺和苯乙烯-马来酰亚胺聚合物。 表征包括pH和金属离子对这些新架构的PEL刷的刷行为的影响的研究。 中子和X射线反射法研究溶胀聚合物薄膜被用作工具，了解刷行为。 还采用了使用标记的聚合物链来单独收集关于聚合物刷的不同组分（刷、侧臂、离子）的信息的中子反射率。 刷是通过带电或受保护的单体的受控自由基聚合从表面生长的。 离子基团通过定制的胺官能链段连接到丙烯酰胺或马来酰亚胺主链，所述胺官能链段包括选定长度和离子基团含量的类肽单元。 聚合物主链上较长的类肽侧链形成瓶刷状结构，而受控的电荷间距和位置选择性地在聚合物主链附近或远离聚合物主链添加库仑应力。 除了传统的垂直生长的刷子，研究小组正在利用新的横向刷生长的几何形状，通过证明微制造能力，使平行的光学和X射线或光学和中子表征刷溶胀在一系列的润湿和电解质条件。 这项研究解决了一些重要的问题上的构象密集的刷，包括链约束和电荷间距的影响。 这些结果有可能进一步推进对影响表面接枝瓶刷聚合物的稳定性和刺激响应性质的因素的基本理解。该奖项反映了NSF的法定使命，并被认为值得通过使用基金会的知识价值和更广泛的影响审查标准进行评估来支持。

In this project funded by the Macromolecular, Supramolecular and Nanochemistry Program in the Division of Chemistry, Professor Christopher K. Ober at Cornell University is developing and studying polyelectrolyte brushes with controlled charged placement. Polymer brushes are special, large molecular structures with polymer chains densely tethered to a surface. They have unique and useful properties including wormlike conformation, compact molecular dimensions, and notable polymer chain end effects due to their compact and confined structures. These particular polyelectrolyte brushes can interact with a biological environment actively or passively depending on the nature of a living system. As such, the brushes are promising materials for biomedical devices, chemical sensors and drug-delivery systems. In this research, synthetic methods are chosen to construct charged polyelectrolyte brushes, allowing systematic investigations of how charge placements changs the swelling, shape, mobility, and stability of the synthesized brushes. Characterization is carried out using sophisticated chemical measurement techniques and also includes the effect of solution acidity and metal ions on brush behavior. This research is interdisciplinary in nature and includes international collaborations with researchers in Germany and the United Kingdom. The research program exposes graduate students and associated researchers to international science perspectives. Graduate students serve as mentors and role models to undergraduate students, while at the same time gaini supervisory skills. Undergraduates from Cornell University take part in the research during the academic year while students from other schools with an emphasis on underrepresented communities participate in research during the summer months. Outreach activities include high school students and teachers through organized workshops. This research is focused on the preparation and study of a series of model poly(electrolyte)(PEL) brushes with carefully tailored placement of cationic and anionic groups used either alone or in combination in a single strand and bottle brush architecture based on acrylamide and styrene-maleimide polymers. Characterization includes study of the effect of pH and metal ions on brush behavior of these new architecture PEL brushes. Neutron and X-ray reflectometry studies of swollen polymer films are used as tools for understanding brush behavior. Neutron reflectivity using labeled polymer chains to separately gather information about the different components (brush, sidearm, ions) of the polymer brush is also employed. Brushes are grown from surfaces by means of controlled radical polymerization of charged or protected monomers. Ionic groups are attached to acrylamide or maleimide backbones through tailored amine functional segments including peptoid units of selected lengths and ionic group content. Longer peptoid side chains on a polymer backbone form bottle brush-like architectures while controlled charge spacing and location selectively add coulombic stress near to or away from the polymer backbone. In addition to conventional vertically grown brushes, the research team is capitalizing on new lateral brush growth geometries through demonstrated microfabrication capabilities that enable parallel optical and X-ray or optical and neutron characterization of brush swelling under a range of wetting and electrolyte conditions. This research addresses important questions on the conformation of dense polyelectrolyte brushes, including the effects of chain confinement and charge spacing. The results have the potential to further advance fundamental understanding of the factors affecting the stability and stimulus-responsive nature of surface-grafted bottlebrush polymers.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.