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

非技术概述：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都很重要，比如低摩擦涂层。聚合物刷通常通过化学键固定在基材上，以增加其稳定性。这个项目将是一个系统的研究，解决聚合物的长度，每单位面积的聚合物分子的数量，以及沿分子的局部电荷分布对电刷稳定性和附着的作用。它将使用具有上述分子刷属性逐渐和连续变化的标本进行。将引入一种新方法，通过选择性地破坏将大分子附着在衬底上的硅氧键，可以从技术上重要的衬底（如二氧化硅）上去除分子聚合物刷。拟议工作的科学方面将辅以外联和教育活动。它们包括i)培训研究生，ii)在小学开展教育外展活动，iii)吸引妇女，未被充分代表的少数民族和当地K-12教师参与研究活动，与北卡罗来纳州立大学的科学之家和工程之家项目以及三角MRSEC项目协调，以及iv)为研究三角地区的学生和教师组织国内和国际软材料科学会议。技术概述：本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，以及它们在固体表面上的分子量、接枝密度（即单位面积上聚合物接枝的数量）和电荷密度（对于聚电解质刷）的函数。本文将系统地研究聚电解质电刷从衬底上解接枝的过程，利用组合组装方法研究分子量、接枝密度和电荷的空间分布（以及它们之间的相互作用）对电刷稳定性的影响。了解大分子接枝上的电荷分布及其与接枝分子量和密度的相互作用，对于许多使用带电聚合物刷的应用是重要的。“按需”化学脱接枝方法将被引入并用于表征由聚合“接枝”合成的聚合物接枝的性质（即分子量、接枝密度和聚合后改性制备的刷子的化学结构）。结合选择性分析方法，将获得有关接枝分子量和化学结构的完整信息。新的模式方法将使形成复杂的化学模式与可调的组成变化跨越模式边界。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化学异质性的定制空间分布的复杂化学模式铺平了道路。

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.