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

非技术综述：聚合物刷子分子是附着在表面的长分子链。这种结构在许多技术应用中都很重要，例如低摩擦涂层。聚合物刷子通常通过化学键固定在衬底上，以增加其稳定性。这个项目将是一项系统的研究，探讨聚合物长度、单位面积的聚合物分子数量以及分子上局部电荷的分布对刷子稳定性和附着性的影响。它将使用以上述分子刷属性的渐进和连续变化为特征的样本来进行。将推出一种新的方法，通过选择性地破坏附着在衬底上的大分子的硅氧键，从二氧化硅等具有重要技术价值的副产品中去除分子聚合物刷子。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)在一所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的K-12教师参与研究活动，与北卡罗来纳州的科学之家和工程之家计划和三角MRSEC计划协调，以及iv)为研究三角地区的学生和教职员工组织国内和国际软材料科学会议。技术摘要：该项目的主要目标是详细了解中性和带电聚合物刷子的稳定性作为分子量、接枝密度(即单位面积上的聚合物接枝数量)的函数，固体表面的电荷密度(用于聚电解质刷子)。系统地研究聚电解质刷从底层基材上的接枝，利用组合组装方法解决分子量、接枝密度和电荷的空间分布(以及它们之间的相互作用)对刷子稳定性的影响。了解大分子接枝过程中电荷分布的作用及其与接枝物的相对分子质量和密度的相互作用，对于许多利用带电聚合物刷子的应用具有重要意义。“按需”化学降解法将被引入并用于表征通过“接枝”聚合合成的聚合物接枝的性能(即聚合后改性制备的聚合物接枝的相对分子质量、接枝密度和刷子的化学结构)。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。新的图案化方法将使复杂的化学图案的形成具有跨图案边界的可调节的成分变化。后一种策略不仅提供了完全表征通过“接枝”聚合生长的聚合物的属性的能力，而且还为产生具有定制的表面化学异质性的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.