Effect of Stress Relief and Ionic Charge on Polyelectrolyte Brush Behavior

聚合物是通过将数百个称为单体的小分子亚单位连接成长链而形成的大分子。根据单体的化学结构，聚合物既可以是光滑的(如特氟龙)，也可以是粘性的(如胶带)。通过改变单体，人们可以创造出防止细胞粘连的表面，使它们更好地用于医疗用途。自然界通过将带电的聚合物片段附着到表面，形成类似刷子的结构来实现这一点。虽然这些刷子聚合物具有独特的性能，可能会对社会产生重大影响，但它们也构成了重大挑战。带电基团的密集堆积可以拉伸化学键，在极端情况下，键可能会断裂。在化学系高分子、超分子和纳米化学项目的支持下，康奈尔大学的Ober教授正在创造和研究新的聚合物刷子，这些刷子不仅是有效的涂层，而且具有很长的使用寿命(即不含容易断裂的键)。合作者Ryan教授(谢菲尔德大学)和Ruehe教授(弗莱堡大学)正在帮助表征聚合物结构。除了其科学影响，该项目还通过教育本科生和研究生成为具有全球意识的跨学科科学家而造福社会。表面结合的瓶刷聚合物可能是人体减震部件的合成模拟物，因此，该项目在大分子化学之外的更广泛的科学影响可能是相当大的。对聚电解质刷子行为的深入了解也有助于理解生物分子、细胞和微生物在表面上的附着，从而被用于控制海洋工业船舶上不必要的粘连。研究小组正在创建和研究一系列稳定的模型聚合物刷子，其离子基团在单股和瓶刷结构中都有精心定制的放置。正在研究与电荷、可溶物质的结合和附着有关的物理现象，以及导致刷子断裂的相当不寻常的机械力化学情况。Ober教授和他的合作者正在准备专门定制的聚电解质刷子，这些刷子具有精选的垂直和水平刷子结构，并研究它们的物理性能。离子基团直接连接到丙烯酸酯或甲基丙烯酸酯聚合物主链上，或通过具有精确离子基团间距和位置的量身定制的类肽单元序列连接。限制是通过使用纳米涂层来控制的，其中图案大小与刷子的高度(数十纳米)相当。用一价阳离子和多价阳离子研究了阳离子电荷的影响。表征活动包括：在一系列润湿和电解液条件下对刷子膨胀和收缩的X射线散射研究，以及使用标记聚合物链分别收集不同组分(主干、侧臂、离子)的信息以绘制带电聚合物刷子的详细图像的中子反射率研究。研究生是本科生的导师和榜样，同时也获得了管理技能。来自康奈尔大学的本科生在学年参加，而来自其他学校的REU学生则在暑期参加研究，重点是代表人数不足的学生。从这些研究方案中学到的经验被整合到高中教师的课程、教师研究经验(RET)方案和教师讲习班中。

Polymers are large molecules formed by linking together hundreds of small molecular sub-units called monomers into long chains. Depending upon on the chemical structure of the monomer, the polymer can either be slippery (like Teflon) or sticky (like tape). By changing the monomer, one can create surfaces that prevent adhesion of cells, making them better for medical uses. Nature accomplishes this by attaching charged polymer segments to surfaces, forming structures that resemble brushes. While these brush polymers offer unique properties that could have substantive societal impacts, they also pose significant challenges. The dense packing of the charged groups can stretch the chemical bonds and, in extreme cases, the bonds can break. With the support of the Macromolecular, Supramolecular and Nanochemistry program of the Chemistry Division, Professor Ober at Cornell University is creating and studying new polymer brushes that are effective coatings but also have long lifetimes (i.e., do not have bonds that easily break). Collaborators, Professor Ryan (University of Sheffield) and Professor Ruehe (University of Freiburg), are helping to characterize the polymer structures. In addition to its scientific impact, the project benefits society by educating undergraduate and graduate students to become globally aware, interdisciplinary scientists. Surface-bound bottlebrush polymers are potentially synthetic mimics for shock absorbing components in the human body, thus, the broader scientific impact of this project outside of macromolecular chemistry is potentially quite large. Insights into the polyelectrolyte brush behavior may also help in the understanding the attachment of biomolecules, cells and microorganisms to surfaces and thus be used to control into unwanted adhesions on ships for the marine industry.The research team is creating and studying a series of stable model polymer brushes with carefully tailored placement of ionic groups in both single strand and bottlebrush architectures. Physical phenomena associated with charge, binding and attachment of soluble species, and the rather unusual case of mechanochemistry that leads to brush breakage are being investigated. Professor Ober and his collaborators are preparing specially tailored polyelectrolyte brushes with selected vertical and horizontal brush architectures and studying their physical properties. Ionic groups are attached directly to the acrylate or methacrylate polymer backbone or through tailored sequences of peptoid units of precise ionic group spacing and location. Confinement is controlled by the use of nanopatterning in which the pattern sizes are comparable to brush height (tens of nanometers). The effect of cation charge is studied using a range of mono- and multivalent cations. Characterization activities include: X-ray scattering studies of brush swelling and shrinkage under a range of wetting and electrolyte conditions and neutron reflectivity studies using labeled polymer chains to separately gather information about the different components (backbone, sidearm, ions) to develop a detailed picture of the charged polymer brush. Graduate students serve as mentors and role models to undergraduate students, while at the same time gaining supervisory skills. Undergraduates from Cornell University take part during the academic year while REU students from other schools with an emphasis onunderrepresented students participate in research during the summer months. Lessons learned from these research programs are integrated into lessons for high school teachers in a Research Experiences for Teachers (RET) program and in teachers' workshops.