This research program will examine the synthesis, characterization and lithographic processing of "grown from" di- and triblock copolymer brushes. By combining brush growth and self-assembly with precision patterning a variety of new polymer micro- and nanostructures will be created that are not easily produced by other means. A key aspect of the proposed research is a focus on immiscible block segment combinations that react in opposite ways to the radiation used during lithographic patterning. By using one phase that crosslinks and one that is scissioned (and easily removed), new periodic structures, porous materials, brush membranes, nanosheets and nanoribbons will be formed. Through brush growth the composition and height will be set and through patterning lateral size and shape will be determined. Advanced patterning methods will initially include electron beam techniques and will subsequently involve deep UV processes. In order to speed evaluation of brush architecture and its effect on pattern formation, the use of initiator density gradients and brush segment size gradients will be employed. Mixed brushes, binary brushes and block copolymer brushes consisting of crosslinkable and scissionable segments will be investigated. Characterization of the brushes before and after patterning will be made using a variety of analytical tools including X-ray reflectometry, grazing incidence (GI) SAXS and WAXS, neutron reflectivity and near edge X-ray absorption fine structure (NEXAFS) measurements. Each technique will provide information about the internal or surface organization of the material and will aid our understanding of the structures produced. Neutron reflectivity in particular will provide information about the brush chain conformation as the brush undergoes the patterning process. Several model systems will be investigated to better understand the process limitations and the possible architectures that can be produced from these brushes. Mixed gradient brushes, supported membranes and untethered nanosheets and nanoribbons will be explored. It is anticipated that applications for these brushes will include new membranes for water purification, nanochannels for small-scale fluidic devices and new nanopatterned strucures from brush gradients.
NON-TECHNICAL SUMMARY:
Polymer brushes are ideal structures to interface the surface of a material with its environment. Like many natural surfaces, polymer chains extend from a surface and provide an organic coating with functional groups that can be modified or used in a number of applications. Along with systematic synthesis and characterization of these materials, there are prospects for making brush surfaces with gradient controlled properties, nanosheets with the ability to wrap drugs and other useful materials for later release, new membranes for water purification to help better improve drinking water in arid regions and nanochannels that will enable transport of fluids in small devices such as sensors. The research program will act as a mechanism to engage undergraduates in polymer science and materials research. Graduate students will serve as mentors and role models to these young students, while at the same time gaining supervisory skills. Graduate students will have an opportunity to work with the research groups of our collaborators and to take part in exchange visits. Undergraduates from Cornell will take part during the academic year while REU students from other schools with an emphasis on underrepresented students will participate in research during the summer months. Cornell undergraduates taking part in this program will be encouraged to take internships at the companies and university labs we will interact with. Lessons learned from these research programs will be factored into programs in which the PI and graduate student volunteers interact with high school teachers. Patterned brushes make interesting visual aids because hydrophobic brushes can repel water. Sample brushes on substrates will be made available to interested teachers the PI will meet at teacher workshops offered by Cornell.
