Effect of Stress Relief and Ionic Charge on Polyelectrolyte Brush Behavior

聚合物是由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，聚合物可以是滑的（像特氟龙）或粘的（像胶带）。通过改变单体，人们可以创造防止细胞粘附的表面，使它们更好地用于医疗用途。大自然通过将带电的聚合物片段附着在表面上，形成类似刷子的结构来实现这一点。虽然这些刷聚合物具有独特的特性，可能会对社会产生重大影响，但它们也带来了重大挑战。带电基团的密集排列可以拉伸化学键，在极端情况下，化学键会断裂。在化学部大分子、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型聚合物刷，这种刷不仅是有效的涂层，而且具有较长的使用寿命（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（弗莱堡大学），正在帮助表征聚合物结构。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而造福社会。表面结合的瓶刷聚合物可能是人体减震成分的合成模拟物，因此，该项目在大分子化学以外的更广泛的科学影响可能相当大。对聚电解质电刷行为的深入了解也有助于理解生物分子、细胞和微生物对表面的附着，从而用于控制船舶上不必要的粘附。研究小组正在创建和研究一系列稳定的聚合物刷子模型，这些刷子在单链和瓶刷结构中精心定制了离子基团的位置。与电荷、可溶物质的结合和附着有关的物理现象，以及导致电刷断裂的相当不寻常的机械化学现象正在研究中。Ober教授和他的合作者正在准备特别定制的聚电解质刷子，选择垂直和水平的刷子结构，并研究它们的物理性质。离子基团直接附着在丙烯酸酯或甲基丙烯酸酯聚合物骨架上，或者通过精确的离子基团间距和位置的肽基单元的定制序列。约束是通过使用纳米图案来控制的，其中图案尺寸与刷的高度相当（几十纳米）。用一系列单价和多价阳离子研究了阳离子电荷的影响。表征活动包括：在一系列湿润和电解质条件下电刷膨胀和收缩的x射线散射研究，以及使用标记聚合物链分别收集不同成分（主链、侧臂、离子）的信息的中子反射率研究，以形成带电聚合物电刷的详细图像。研究生作为本科生的导师和榜样，同时获得管理技能。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。从这些研究项目中获得的经验被整合到教师研究经验（RET）项目和教师研讨会的高中教师课程中。

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.