Degrafting of polymer brush molecules from substrates: Nuisance or opportunity?

非技术总结：聚合物刷分子是附着在表面上的长分子链。 这种结构在许多技术应用中是重要的，例如低摩擦涂层。 聚合物刷通常通过化学键固定到基底上以增加其稳定性。 该项目将是一个系统的研究，解决的作用，聚合物的长度，每单位面积的聚合物分子的数量，和局部电荷分布沿着刷稳定性和附着的分子。 它将使用具有上述分子刷属性的逐渐和连续变化的标本进行。 将介绍一种新的方法，使分子聚合物刷从技术上重要的substartes，如二氧化硅，通过选择性地打破硅氧键，保持附着在基板上的大分子的去除。 拟议工作的科学方面将辅之以外联和教育活动。 它们包括i）培训研究生，ii）在小学开展教育推广活动，iii）吸引妇女，代表性不足的少数民族和当地K-12教师参加与北卡罗来纳州科学之家和工程之家计划以及三角MRSEC计划协调的研究活动，以及iv）为三角研究区的学生和教职员工组织国内和国际的软材料科学会议。该项目的主要目标是详细了解中性和带电聚合物刷的稳定性与分子量的关系，接枝密度（即，每单位面积的聚合物接枝数）和固体表面上的电荷密度（对于刷）。 将系统地研究从底层衬底上脱接枝的刷，解决分子量，接枝密度和空间分布的电荷（以及它们之间的相互作用）的作用，使用组合组装方法刷的稳定性。 理解电荷分布沿着大分子接枝物的作用及其与接枝物的分子量和密度的相互作用对于利用带电聚合物刷的许多应用是重要的。 “按需”化学降解方法将被引入并用于表征聚合物接枝物的性质（即，分子量、接枝密度和通过后聚合改性制备的刷的化学结构）。 与选择性分析方法相结合，将获得有关接枝分子量和化学结构的完整信息。 新的图案化方法将能够形成复杂的化学图案，其在图案边界上具有可调节的成分变化。 后一种策略不仅提供了充分表征通过“接枝”聚合生长的聚合物属性的能力，而且还为生成具有表面上化学不均匀性的定制空间分布的复杂化学图案铺平了道路。

NON-TECHNICAL SUMMARY:Polymer brush-molecules are long molecular chains attached to surfaces. Such structures are important in numerous technological applications, such as low-friction coatings. Polymer brushes are typically anchored to the substrate via a chemical bond to increase their stability. This project will be a systematic study addressing the role of polymer length, number of polymer molecules per unit area, and distribution of localized electrical charges along the molecules on brush stability and attachment. It will be carried out using specimens that feature gradual and continuous variation of the aforementioned molecular brush attributes. A new method will be introduced that enables removal of molecular polymer brushes from technologically important substartes such as silicon dioxide by selectively breaking the silicon-oxygen bond that holds the macromolecule attached to the substrate. The scientific aspect of the proposed work will be complemented with outreach and education activities. They include i) training graduate students, ii) conducting educational outreach activities at an elementary school, iii) attracting women, underrepresented minorities, and local K-12 teachers to take part in research activities in coordination with NC State's Science House and Engineering House programs and the Triangle MRSEC Program, and iv) organizing national and international scientific meetings in soft materials for students and faculty in the Research Triangle region.TECHNICAL SUMMARY:The principal goal of this project is to gain detailed understanding of the stability of neutral and charged polymer brushes as a function of molecular weight, grafting density (i.e., number of polymer grafts per unit area), and charge density (for polyelectrolyte brushes) on solid surfaces. Degrafting of polyelectrolyte brushes from underlying substrates will be studied systematically, addressing the role of molecular weight, grafting density, and spatial distribution of charges (as well as their mutual interplay) on the brush stability using combinatorial assembly methods. Comprehending the role of charge distribution along macromolecular grafts and its interplay with molecular weight and density of the grafts is important for many applications utilizing charged polymer brushes. "On-demand" chemical degrafting methods will be introduced and employed to characterize the properties of polymeric grafts (i.e., molecular weight, grafting density, and chemical structure of brushes prepared by post-polymerization modification) synthesized by "grafting from" polymerization. In combination with selective analytical methods complete information about the graft molecular weight and chemical structure will be obtained. New patterning methods will enable the formation of complex chemical patterns with adjustable compositional variation across pattern boundaries. The latter strategy not only offers the ability to characterize fully the attributes of polymers grown via "grafting from" polymerization, but also paves the way towards generating complex chemical patterns with tailored spatial distribution of chemical heterogeneities on surfaces.