To promote the progress of polymer science, this project is focused on polymer nanocomposites. Because they underlie so many applications, polymer-nanocomposite research impacts and improves technologies ranging from complex devices, such as energy producing solar cells, to everyday materials, such as lighter packaging. The fundamental issues that the project seeks to address are those that govern the assembly of anisotropic particles in block copolymers. Specifically, the project will produce vertically-oriented, anisotropic particles with controlled regular separations, and in so doing will advance understanding of nanorods and nanoplates in polymeric materials having special geometries such as nanocylinders in a matrix or alternating nanosheets. The resulting insights about how to self-assemble vertically oriented nanoparticles will enable the scientific community to explore a variety of anisotropic properties including molecular, electrical, and thermal transport. A successful outcome of the proposed research will be precise control over the vertical orientation and lateral spacing of nanorods and nanoplates in polymer nanocomposite films, which have potential benefits to society in areas of nanofiltration, sensing, barrier coatings and lighting. Besides producing a well educated, scientifically skilled work force, the integration of research and education benefits society at several levels. Besides graduate education, undergraduates from the US and abroad as well as local Philadelphia high school participants will benefit from research and mentoring. To reach a broad audience, researchers will participate annually in Nanoday@Penn and Philly Materials Day, which attract over 200 high school students and 2000 attendees, respectively. Furthermore, the annual Teachers Materials Science Workshop will continue as well as a unique partnership with Central High School, Philadelphia, which exposes a large minority student population to opportunities in STEM fields.
The thermodynamic and dynamic principles that control vertical alignment of nanorods and nanoplates in block copolymer (BCP) films will be investigated. Anisotropic particles will be grafted with polymer brushes to control their interactions with other particles and BCP. Research objectives are to: (1) Vertically align nanorods in perpendicular cylindrical domains of block copolymers. Metallic, nanophosphor and semiconducting nanorods will be investigated in poly(styrene-b-2-vinyl pyridine) (PS-b-P2VP) and P2VP films. The effect of nanorod diameter and length on vertical orientation is of particular interest, as well as using binary mixtures of nanorods to direct them to specific microdomains. (2) Vertically align nanoplates in perpendicular lamella domains of block copolymers. Graphene oxide, nanophosphor and laponite nanoplates will be investigated in poly(styrene-b-methyl methacrylate) (PS-b-PMMA) and PS films. (3) Investigate the dynamics of nanorod assembly in homopolymer and block copolymer films during solvent annealing. Single particle tracking will be used to measure nanorod mobility. Field theoretic simulations modified to include dynamics will guide experiments and provide insight into the balance between thermodynamics and dynamics that differentiates the final morphology. The research leverages new and continuing collaborations to create novel particle-polymer assemblies, perform in situ characterization, and model vertically aligned polymer nanocomposites. Specifically, dispersion will be studied as a function of particle shape, size and surface chemistry, film thickness and interface interactions, and BCP composition and size. Three-dimensional field theoretic simulations will guide the choice of experimental parameters and provide a thermodynamic framework for understanding the interplay between particle and BCP orientation. BCP morphology will be determined by TEM, AFM and SAXS, particle location by TEM, FIB-SEM and depth profiling by RBS. GISAXS will be used to follow in situ structural evolution during solvent annealing. Optical properties will be characterized by UV-vis spectroscopy. This research benefits from unfunded collaborations with Sandia National Laboratories and the Advanced Light Source.
