The In-Plane Nanostructural Organization of Copolymer Molecules along Polymer / Polymer Interfaces is critical to the development of advanced coatings, in which case the molecular-scale conditions responsible for promoting film stabilization must be fully established and understood. Most studies of this nature consider the interfaces to be laterally homogeneous, especially at long times. The PIs have recently found, however, that addition of an incompatible block copolymer or a core-shell polymer nanoparticle to a thin-film laminate induces discrete heterogeneities along the polymer / polymer interface, thereby indicating that lateral interfacial structuring plays an important role in compatibilization / stabilization. Previous results (i) raise fundamental questions regarding the competition between copolymer self-organization or nanoparticle aggregation and interfacial structuring as functions, and (ii) open new avenues to thin-film polymer laminates for coating and templating technologies. The long range objectives are to: (1.) Understand the type and extent of lateral structuring of diblock copolymers at interfaces between two immiscible homopolymers and how lateral interfacial structuring develops. While most previous studies have concentrated on exploring copolymer structure normal to the interface between two immiscible homopolymers, their previous results demonstrate that such structuring can be highly heterogeneous. In a thin-film laminate, such interfacial heterogeneities may adversely affect thin-film stability. The in-plane structure variations of copolymer molecules along the interface provide experimental evidence of discrete lateral interfacial structuring and warrant in-depth examination. (2.) Utilize the observed phenomena as a controllable means of large-area assembly and patterning of polymer surfaces. The PIs have observed that CSP nanoparticles preferentially segregate to polymer / polymer interfaces, and the extent to which they protrude from the film depends sensitively on the Surface / interfacial energy. The ON/OFF position of these CSP nanoparticles, triggered by a change in surface energy, and the simultaneous capability of organized in-plane structure would make such system convenient candidates for active reflective surfaces and smart tags. An improved understanding of the material and environmental factors governing interfacial structuring is needed. (3.) Interrogate the spatiotemporal organization of block copolymers and CSP nanoparticles at interfaces between two immiscible polymers to acquire valuable guidance in designing efficient interfacial reinforcing and compatibilizing agents. While block copolymers are widely established as macromolecular surfactants, little is known about the early stages of the reinforcing mechanism, far from equilibrium. The PIs past experiments show that the organization of block copolymer molecules or CSP nanoparticles at interfaces cannot be perceived as a simple '1D" problem since discrete in-plane features exist. Understanding the spatiotemporal behavior of such structure is crucial in identifying optimal conditions for compatibilization in relevant polymer systems (blends and thin films).
This project will result in a graduate student being trained to (i) use state-of-the-art analytical methods to investigate thin-film polymer laminates and (ii) develop design and problem-solving skills to generate and analyze, in reproducible, meaningful and insightful fashion, the multicomponent systems outlined in this proposal. As part of his/her graduate program, the student will be required to give two presentation Updates / semester to improve his/her communication and presentation skills in preparation for conference meetings. The PI is currently initiating an international undergraduate senior design program within the NC State College of Engineering and will involve international student teams with this project. The student involved in this project will work closely with students at the Centennial Middle School located on the NC State Centennial Campus for this purpose. Lastly, the PI and co-PI have both been selected, on the basis of a University-wide competition, as mentors for undergraduate Beckman Scholars, and so the research will be augmented with a fully supported, undergraduate research assistant. The scholarly results generated during the course of this project will be disseminated through traditional modes, such as oral/poster presentations at scientific meetings and publication in high-impact scientific journals. Results from this research will be included in two graduate-level courses on blends and interfaces.
