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.
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.
