Collaborative Research: Locking Nanoparticles

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CBET-0756457LuzinovIntellectual Merit The goal of the proposed research is to synthesize and study hybrid nanoparticles 10-100 nm in diameter constituted of an inorganic superparamgnetic core and a mixed polymer brush shell. Mixed polymer brushes refer to monolayers of two unlike polymers end-grafted to the same solid substrate. Mixed brushes grafted onto nanoparticles were successfully used by the PIs to design responsive colloidal systems which change their properties (e.g., interfacial energy and composition, adhesion, adsorption, aggregation, stability, etc.) according to external signals such as solvent quality, pH and temperature. The mechanism of this switching/responsive behavior was shown to originate from the microphase segregation of unlike polymers in the shell, where outside conditions may strongly affect the phase segregation. In this proposal, we suggest the further development of the responsive particle approach to a challenging new system - hybrid nanoparticles with dual responses due to the nanoparticles' specially tailored core-shell structure. The superparamgnetic nanoparticle's core will be coated by the mixed brush shell composed of a water soluble polymer and a hydrophobic weak polyelectrolyte. Solubility of the latter polymer in aqueous solutions can be tuned by pH, ionic strength, and temperature. For example, at room temperature and at pH 7 this polymer segregates to the particle core and the mixed brush forms radially segregated shell. The particles with a stratified mixed brush shell will demonstrate non-sticky properties and form stable suspensions in aqueous solutions in a broad range of pH values and ionic strengths. They will be stabilized due to the steric repulsion mechanism by the polymer brush (forming the outer shell) prepared from a water soluble polymer. The situation can be dramatically changed by applying an external magnetic field. The magnetic forces will overcome the steric repulsion and the particles will interact via the inner brush shells. Thus, this external magnetic field can turn on interactions between particles themselves, or between particles and the targeted substrate. The interaction remains unchanged even after removal of the external magnetic field due to the strong interactions between the inner shells. This mechanism is termed here the "locking mechanism". The interaction between the inner shells can be tuned and switched by the pH and temperature in their host environment. Thus, the particles can be unlocked by applying external stimuli. The nanoparticles proposed here will respond to an external magnetic field and, at the same time, they will respond to changes in pH, ionic strength and temperature. Properties of the particles' colloidal dispersion will be tuned/switched by a combination of a magnetic field and chemical/physical stimuli. In the proposed research we will aim: (1) developing the synthesis of the nanoparticles with the dual response; (2) studying the responsive behavior of the particles, and (3) switching between an adhesive and a non-adhesive particle shell to turn the adsorption of particles on various surfaces and their aggregation on and off. Broader Impact The obtained results are expected to substantially impact nanoscience and nanotechnology fields involving nanoparticle technologies and the design of complex functional materials and devices. The magnetically responsive particles will be used for a range of important technical, biological and medical applications where the specific versus nonspecific particle interactions can be switched on in an external magnetic field. Another priority of the proposed project is the involvement of the brightest high school, undergraduate and graduate students in modern nanostructured materials research. The project will train these students in nanoscience, nanotechnology, particulate science and surface science. Students will benefit greatly from this project's interdisciplinary nature. Significant effort will be directed to increasing the number of students, especially minorities and women, who pursue advanced degrees in science and engineering.