The proposed research will focus on the development of a novel class of organic/inorganic hybrid nanoparticles as building blocks for hierarchically self-assembled materials. The fundamental aspects of the synthesis, characterization and assembly of polymer coated magnetic nanoparticles will be the focus of this proposal. The intellectual merit of the proposed research is the ability to prepare complex composite materials possessing controlled structure on molecular, nano- and mesoscale regimes. The development of a versatile synthetic methodology to prepare a library of functional ferromagnetic colloids will be initially pursued. Central to this approach is the use of well-defined polymers to prepare and functionalize ferromagnetic nanoparticles that are capable of 1-D magnetic assembly. Controlled radical polymerization will be central in the design and synthesis of polymeric surfactants. A second critical effort that will be investigated is the controlled assembly of functional ferromagnetic nanoparticle on surfaces, in solution and in polymer thin films. The effect of particle size, magnetization and applied magnetic fields will be investigated to determined optimal conditions for 1-D assembly and alignment in various matrices. Development of these areas is anticipated to enable the assembly and covalent linkage of functional magnetic nanoparticles into permanently linked chains. These functional 1-D assemblies are expected to be mesoscale analogues to polymer chains. Characterization of these materials using various imaging techniques (e.g., AFM, TEM), thermal analysis and mechanical property evaluation will be conducted to ascertain structure-property correlations of assembled materials possessing different morphologies.
NON-TECHNICAL SUMMARY: Organic polymers and metallic particles will be synthesized and combined to prepare core-shell composite materials possessing an organic shell with tunable composition and an inorganic magnetic core. These materials will be hybridized on the nanoscale as an approach to prepare novel materials with synergistic properties. The magnetic properties of the materials will be utilized to self-assemble these hybrid nanoparticles into fiber-like structures spanning microns on length. This work is anticipated to impact a number of areas in microelectronics and optoelectronic devices due to the ability to control structure over a broad range of length scales. The proposed research is highly interdisciplinary and offers opportunities for students at high school, undergraduate and graduate levels to appreciate the importance of polymers and nanomaterials. Integration of the proposed research with educational outreach will be achieved by the mentoring of high school students and teachers in research experiences carried out at the University of Arizona by the principal investigator. Research implemented by this student-teacher team will be disseminated by integrated interactions with undergraduate research programs on campus. Emphasis will be placed on the mentoring and development of students from under-represented minorities in Tucson.
, was a project lead by Prof. Jeffrey Pyun in the Department of Chemistry at the University from 3/01/12 to 8/31/12. Over this period of time, several graduate students, undergraduate students and postdoctoral researchers contributed to the project, resulting in two Ph.D. graduates and over fifteen publications in high quality peer-reviewed Chemistry journals. The nature of the research developed during this contract was in the general area of polymeric and nanomaterials, where polymers and magnetic nanoparticles were synthesized using new chemical methods to prepare a new family of nanocomposite materials. In principle, these new materials marry the benefits of functional organic materials and the unique properties of inorganic materials to create a new "hybrid" designed into a core-shell type particle object. These types of materials are already important and widely used for information storage in the form of magnetic tapes and plastic magnets. However, exploration of these types of hybrid core-shell particles with the approach pursued in this project enabled new avenues for these materials in information storage and energy applications. The system that was developed can be envisioned to comprise of an outer coating of polymers chains, which serve as "hairs" to stabilize an inner core comprised of an inorganic magnetic nanoparticle, primary composed of metallic cobalt. In principle, these core-shell particles are nanoscopic versionz of plastic magnetic balls and toys that are commonly enjoyed by young toddlers and children. The key feature that this system exploits on the nanoscale is the ability to "self-assemble" to one-dimensional fiber-like assemblies from magnetic attractions between particles. From this central premise, we built a platform of new materials by modifying the nature of either the polymer hairs, or the composition of the magnetic nanoparticle. The following are the key accomplishments, described by representative figures in publications on this research: Publication #1: Synthesis of Polymer Coated Ferromagnetic Nanoparticles in Multi-Gram Quantities with Tunable Variation of Particle Size," Bull, M.M.; Chung, W.-J.; Rasmussen, S.G.; Kim, S.-J.; Shim, I.; Paik, H. –J.; Pyun, J. J. Mater. Chem. 2010, 20, 6023-6025. In this report, we developed a one-pot synthesis of polymer coated ferromagnetic cobalt nanoparticles. In the field of nanoscience, the synthesis of multi-gram quantities of nanoparticle materials is challenging, which was a major accomplishment for our system. Using a two-step total synthesis, we were able to prepare polystyrene coated cobalt nanoparticles on scales up to 25 g per batch and were also able to tune particle size from 20-50 nm. Publication #2: Dipolar Organization and Magnetic Actuation of Flagella-like Nanoparticle Assemblies ," Benkoski, J.J.; Breidenich, J.L.; Uy, O. M.; Hayes, A.T.; Deacon, R.; Land, B.H.; Spicer, J.M.; Keng, P.; Pyun, J. J. Mater. Chem. 2011, 21, 7314-7325 With these polymer-magnetic nanoparticles in hand, in collaboration with Dr. Jason Benkoski at the Johns Hopkins Applied Physics Laboratory, we were able to apply these core-shell nanoparticles as magnetically responsive materials. Using an external magnetic field source fabricated in the Benkoski group, our core-shell magnetic nanoparticles are assembled into fibers that mimicked either cilia, or flagella. These "artificial cilia", or "artificial flagella" were among the smallest ever fabricated and made wholly via "bottom up" assembly with external fields. Shown in figure 2 is a representative image of the artificial flagella fabricated from 20 nm magnetic particles assembled into a single "tail" and bound to a single iron oxide particle (~200-500 nm). Publication #3: "Colloidal Polymerization of Polymer Coated Ferromagnetic Nanoparticles into Cobalt Oxide Nanowires," Keng, P.; Kim, B.; Shim, I.-B.; Sahoo, R.; Veneman, P.E.; Armstrong, N.R.; Yoo, H.; Permberton, J.E.; Bull, M.M.; Griebel, J.J.; Ratcliff, E.L.; Nebesny, K. G.; Pyun, J. ACS Nano 2009, 3 (10), 3143-3157. A new concept developed with these polymer coated cobalt nanoparticles was to use these as chemical reagents and polymerize these nanoparticles into polymer-like structures composed of cobalt oxide (Co3O4). In this system, the inherent magnetic assembly of cobalt nanoparticles formed 1-D assemblies that could be directly fused by a simple oxidation reaction. This one-step process was reminiscent of traditional polymerization in organic chemistry, except in this case using cobalt nanoparticles as "colloidal monomers" in "colloidal polymerization." We further found upon characterization of these Co3O4 nanowires that these materials possessed useful electrochemical and catalytic properties which could be exploited as electrodes for Li-batteries or, photocatalysts for water splitting (both of which are important energy problems). This lead us to further expand upon cobalt nanoparticles and cobalt oxide nanowires to introduce new useful functionality based on noble metal NP inclusions (e.g., Au, Pt, ), or semiconductor nanorods (CdSe@CdS). The highly interdisciplinary nature of this work at the interface of chemistry, physics and engineering afforded a unique skill set to researchers working on this project.
