CAREER: Nanoscale Resolution of Near-Interface Crystallization in Multicomponent Semicrystalline Polymeric Materials

PART 1: NON-TECHNICAL SUMMARY Semicrystalline polymers comprise ~70% of all synthetic plastics, and they are pervasive in daily life in packaging, transportation, and high-technology applications like microelectronics. Semicrystalline polymers are often used in the form of multicomponent polymeric materials, e.g., multilayer polyethylene/poly(ethylene terephthalate) films for packaging and carbon fiber-reinforced composites for transportation. A key feature of these multicomponent materials is the presence of a large quantity of polymer/polymer or polymer/filler interfaces. Understanding the effects of these interfaces on polymer crystallization is essential to the predictive design of multicomponent materials with desired crystalline structures and properties. Unfortunately, such a fundamental understanding is lacking. This project will work toward closing the fundamental knowledge gap in interfacial effects and polymer crystallization, using a new fluorescence technique with a nanoscale spatial resolution. The fundamental knowledge gained from this research will advance the development of new multicomponent materials with optimized crystalline structures and properties, which can contribute to a broad range of applications such as food packaging and biomedical devices. This project will provide an integrated research and educational experience for graduate students, undergraduate students, and high-school students, including members of underserved groups. The principal investigator and students will also develop education-oriented online videos and hands-on demonstrations to engage the general public and attract K-12 students into STEM fields. PART 2: TECHNICAL SUMMARY This project’s research goal is to advance fundamental understanding of the interfacial effects on crystallization in multicomponent semicrystalline polymers, using a new fluorescence technique with a nanoscale spatial resolution. The principal investigator (PI) plans to achieve this goal by strategically placing trace amounts of “reporter” (i.e., crystal-sensing) fluorescent dye labels at controlled distances from interfaces to elicit fluorescence-based information about local crystallization and thus interfacial effects. Towards this goal, the PI and students will pursue three research thrusts: (1) Understand the role of fluorescence as a crystallization-sensing mechanism by selectively placing the dyes in rigid vs. mobile amorphous fraction regions to deconvolute their contributions to the overall fluorescence; (2) Study near-interface crystallization by location-specific fluorescence and complementary methods such as grazing-incidence X-ray scattering; (3) Unveil polymer/polymer and polymer/substrate interfacial effects on crystallization and their perturbation length-scale. Material studies will focus on degradable poly(L-lactic acid) (PLLA) as a model semicrystalline polymer to advance the design of new PLLA-based multicomponent materials with desired structures/properties and improved sustainability, including multilayer films, composites, blends, and block copolymers. The education/outreach plan will broaden the reach and benefits of this CAREER research at multiple levels: (1) The PI and students will reach out to the general public through online educational videos on semicrystalline polymers; (2) The PI will develop a new lab module on plastic packaging and leverage the existing research programs at ASU to train graduate students, undergraduate students, and high-school students on polymer synthesis and characterization; (3) The PI and students will develop hands-on demonstrations at ASU Open Door to stimulate local K-12 students’ interest in polymers and STEM careers. . This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.