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在一起形成长链的大分子。根据单体的化学结构，聚合物可以是光滑的（如特氟龙）或粘性的（如胶带）。 通过改变单体，人们可以创造出防止细胞粘附的表面，使它们更适合医疗用途。大自然通过将带电的聚合物片段附着在表面，形成类似刷子的结构来实现这一点。虽然这些刷状聚合物提供了可能具有实质性社会影响的独特性能，但它们也带来了重大挑战。带电基团的密集堆积可以拉伸化学键，在极端情况下，化学键可能会断裂。在化学系的大分子，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，这些聚合物刷是有效的涂层，但也具有长寿命（即，不具有容易断裂的键）。合作者Ryan教授（谢菲尔德大学）和Ruehe教授（弗赖堡大学）正在帮助描述聚合物结构。除了其科学影响外，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来造福社会。表面结合的瓶刷聚合物是人体减震成分的潜在合成模拟物，因此，该项目在大分子化学之外的更广泛的科学影响可能相当大。 深入了解生物分子、细胞和微生物在表面上的附着行为也可能有助于理解生物分子、细胞和微生物在表面上的附着，从而用于控制海洋工业船舶上不必要的粘附。研究团队正在创建和研究一系列稳定的模型聚合物刷，这些聚合物刷在单链和瓶刷结构中都有精心定制的离子基团位置。正在研究与电荷、结合和可溶性物质附着有关的物理现象，以及导致电刷断裂的机械化学的相当不寻常的情况。奥伯教授和他的合作者正在准备专门定制的垂直和水平刷结构的刷子，并研究它们的物理特性。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，或通过精确离子基团间距和位置的类肽单元的定制序列连接。限制是通过使用纳米图案化，其中图案的大小是相当的刷高度（几十纳米）的控制。阳离子电荷的影响进行了研究，使用一系列的单和多价阳离子。 表征活动包括：在一系列润湿和电解质条件下的刷溶胀和收缩的X射线散射研究和使用标记的聚合物链的中子反射率研究，以分别收集关于不同组分（主链、侧臂、离子）的信息，以开发带电聚合物刷的详细图片。 研究生作为导师和榜样，本科生，而在同一时间获得监督技能。康奈尔大学的本科生在学年期间参加，而来自其他学校的REU学生则在夏季参加研究，重点是代表性不足的学生。从这些研究项目中吸取的经验教训被整合到教师研究经验（RET）项目和教师研讨会中的高中教师课程中。

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.