Polymers underlie an untold number of technologies ranging from consumer products to electronics. Despite recent progress in the field, a full understanding of the flow properties of entangled polymer solutions is lacking. A major challenge in polymer processing arises from the unusually complex flow dynamics of branched polymers, wherein molecular topology ultimately determines macroscopic material response. Traditionally, bulk rheological methods have been used to study polymer flows, but these methods average away individual molecular motions. To overcome these challenges, a new molecular approach to probe dynamics is required.
Intellectual Merit. The proposed research aims to provide a molecular-level view of branched polymer dynamics in flow using single molecule methods. Polymer stress relaxation and the non-linear flow properties of entangled comb polymers will be studied, and single polymer data obtained from experiments will be compared to theoretical models. In this way, direct observation of backbone and branch relaxation at the molecular level will be pursued, facilitated by using dual-color fluorescent dyes on the backbone and side-chain branches. The proposed research relies on three innovative technologies developed in the PI's lab: (1) custom synthesis of linear and branched single stranded DNA (ssDNA) polymers with properties similar to synthetic chains, (2) dual-color labeling of branched ssDNA polymers at architecturally-specific locations such as backbones and branches, and (3) automated microfluidic-based flow systems that allow for controlled fluid flows, combined with single molecule imaging of polymer conformations with nanoscale resolution.
Broader Impacts. This research will provide a detailed molecular-level view of entangled topological networks, thereby establishing a direct link between the molecular properties of branched polymers and macroscopic flow properties (e.g., viscosity and stress). The proposed combined custom synthesis and molecular imaging approach will allow for the guided design of polymeric materials with tailored properties that give rise to a desired processing response. In this way, the proposed work will provide crucial insight into the improved processing and manufacturing of branched polymers. The proposed work also integrates cutting-edge research in molecular rheology with the educational training of graduate and undergraduate students, which is accomplished by mentoring students to work in a collaborative workspace. Educational outreach will be incorporated by working with the Illinois iRise program, which actively engages local K-12 high school science teachers in the Urbana-Champaign area to develop experimental labs for the classroom, and mentors middle and high school students from underrepresented groups, with a particular focus on sparking an interest in science through hands-on experiments. The proposed research also includes participation in the Multicultural Engineering Recruitment for Graduate Education (MERGE) program at the University of Illinois, which aims to recruit students from underrepresented groups in engineering.
