The Analytical and Surface Chemistry Program of NSF Division of Chemistry is supporting the research program of Professor Mary Elizabeth Williams in the Department of Chemistry at The Pennsylvania State University. Professor Williams and her students focus on a project titled "Magnetic Manipulation and Selective Isolation of Nanoparticles and Nanoparticle Assemblies." Small particles that have nanometer scale dimensions have unique properties that make them interesting for biomedicine, catalysis and sensing. The Williams research group is particularly interested in small magnetic particles, which can be pulled and trapped using magnets. When these are chemically linked together, the particles are expected to form new materials with improved properties for the above applications. This research project focuses on magnetically manipulating and pulling particles with a high level of control based on their size, magnetic properties, and number of linked particles. The study provides excellent training opportunities for undergraduate and graduate students and postdoctoral research associates in the highly multidisciplinary and cutting edge research field of nanoscience and nanotechnology.
To be able to accurately analyze and separate complex mixtures of nanoparticles, a magnetic separation system called that incorporates an electromagnet into a capillary system was designed. Control over the magnetic flux density allows for application of magnetic programs that (in conjunction with variation in solvent flow rate) enable analysis of model magnetic nanoparticles and separation of particle mixtures. The isolated particles have narrower size distributions than as-prepared particles, demonstrating the effectiveness of this differential magnetic catch and release (DMCR) technique for purification and isolation of magnetic particles. Systematic and detailed study of the parameters necessary to optimize separations of magnetic nanoparticles by DMCR was undertaken and the impacts of solvent viscosity, retention time, etc. on the efficiency of the separation were evaluated. The technique was also expanded to preparatory-scale samples of magnetic nanoparticles while retaining the separation efficiency, making it feasible to utilize the method in real-world applications. In collaboration with Professor Ray Schaak’s group, we then focused on applying DMCR to the study of real nanoparticles, focusing on two important hybrid nanocrystal systems, Au-Fe3O4 and FePt-Fe3O4. We demonstrated that pure hybrid nanoparticles have substantially different magnetic properties compared to the as-synthesized materials: the magnetization values are more accurately determined, and magnetic polydispersity was identified in morphologically-similar hybrid nanoparticles that are otherwise not detectable. This work has broad impacts because it demonstrates the importance of analytical separations of nanostructures, a method with which to accomplish it, and revealed new physical and mechanistic insights. Our interest in chemical modification and transport of nanoparticles led us to also consider their transport as a function of size through porous media in aqueous and nonaqueous solutions. These initial studies provided a straightforward means with which to understand and control particle motions in confined geometries or complex media. Detailed investigation focusing on measuring the role of surface chemistry on the transport of particles through pores. Transport of particles in aqueous solutions through porous media has implications for how nanoparticle effluents may be transported in the environment. Our results demonstrated that both the pore and particle surface chemistries play important roles in flux and permeability, and provide the framework for studying transport.
