This is a collaborative project with CBET-0731319, Colorado School of Mines.
Control of polymer interfacial properties independent of bulk properties is crucial in many applications and processes, and can be achieved by enrichment of the interface by functionalized molecules. Since desired functional groups may not be favored at the interface, a general strategy is needed for promoting this enrichment. Our goal is to use novel nonlinear chain architectures to create a thermodynamic driving force to bring functionalized molecules to an interface without relying on interface-seeking groups. Foster's group (U. Akron) has shown that long-chain branching can indeed drive a polymer to or away from an interface. These experiments are only in partial agreement with mean-field theory predictions by Wu (Colorado School of Mines). Cyclic molecules are moreover predicted to produce an interfacial driving force independent of chemical group and polydispersity. The investigators will make the first measurements on blends containing cyclic molecules. To advance the understanding of both bulk and interfacial thermodynamics needed to move this concept to useful applications, they will integrate synthesis of well-defined molecules (Quirk, UA), experimental measurement of blend behavior (Foster), and development of new theory (Wu).
Intellectual merit: A new self-consistent field formalism will be developed to treat intra- and inter-molecular interactions at the pair (non-mean-field) level, to account for explicit topological effects as well as interplay between chemical group effects and chain conformation. The critical physical issues for blends of nonlinear chains are anticipated to be swelling/collapse and crowding due to monomer-monomer interactions. An early objective will be to explain existing data on surface segregation and related bulk thermodynamics for mixtures with branched chains. Experimental measurements of interfacial segregation with neutron reflectometry and surface enhanced Raman spectroscopy, as well as of the bulk thermodynamic interaction parameter, will be made on blends of cyclic chains for the first time. Together with new information on blends with branched chains, these data will be compared with and used to refine theory. Synthesis of well-defined branched and cyclic molecules by anionic polymerization will enable particularly incisive comparisons. Comparison will also be made with blends containing polydisperse cyclic chains synthesized using ring-opening polymerizations with a Grubbs catalyst that has commercial promise. To demonstrate our approach, they will functionalize a polymer surface with surface-avoiding polar groups by attaching them to molecules with specifically designed nonlinear architectures.
Broader impacts: The thermodynamic modeling of long-branched and cyclic polymers enabled by this study will be applicable to the design of additives for bulk and surface rheology modification (e.g. in lubricant oils and to control droplet formation or aid processing), for adhesives and sealants (e.g. siloxane materials), and for drug delivery (e.g. dendronized polymers). It will also be applicable for biological systems containing branched and cyclic polymers such as polysaccharides and nucleic acids. Education will be integrated with research by having graduate students join in research activities at the partner university and national laboratories, and by including undergraduates through U. Akron's REU program. Faculty and graduate students will prepare video modules with the Akron Global Polymer Academy for web and classroom-based outreach to K-12 students. These modules will describe basic concepts from the research, such as reasons for the mixing and demixing of molecules, how scattering of light and neutrons reveals structure,and how Raman spectroscopy can be sensitive to the composition of surfaces.
