Magnetic interactions for selective assembly and reconfiguration of colloids

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New materials with desired properties are often formed by binding together nano- or micron-sized particles in a fast, precise fashion. This task has proven challenging because available experimental methods do not provide the desired control over the particle binding and assembly process. The goal of this project is to use external magnetic fields to provide a new way to control the assembly and organization of nano- and micron-sized particles in aqueous solution. The project focuses on effects of particle shape, solvent properties, and the strength of the applied magnetic field on assembly and structuring of the particles. The primary goal of the project is to establish an experimental strategy for rapid fabrication of precise structures of microparticles, which otherwise requires complex synthetic procedures. The project will use the assembled structures as micron-sized vehicles for controlled motion and delivery of molecules at a specified location within the solvent. The subsequent formation of a polymeric structure along the path of the moving microparticle will be a new class of polymer printing, where particle assemblies would be used to control the printed geometry. The project will provide opportunities for undergraduate and graduate students to develop new skills in the emerging field of reconfigurable materials. The research team will be involved with outreach activities for visually impaired and middle-school students. In addition, the investigator will work with Baton Rouge Community College to introduce their students to education and research opportunities available at LSU. This project seeks to answer a fundamental question in particle assembly: Can non-specific magnetic interactions be used for directing selective assembly and reconfiguration of multi-component colloidal structures? The hypothesis behind the project is that the magnetic potential energy landscape around a colloidal particle can be designed by altering its shape/surface anisotropy and magnetic susceptibility contrast with the dispersing medium, which may allow for selective attachment of a guest particle to a specific binding site on a host microparticle. The project will test the hypothesis and address the abovementioned question by examining the assembly and reconfiguration of iron patched colloidal particles in external magnetic field. The project aims to (1) Direct the assembly process by designing magnetic energy landscapes around a colloidal particle, (2) Identify the effect of particle shape on the assembly of the mixture of patchy and non-patchy colloids, (3) Understand the role of external magnetic field characteristics on the reconfiguration of the assembled structures, and (4) Develop a particle-based patterning technique using the assembled structures as active and self-propelling sub-units to drive a polymerization process in a liquid phase. The project will provide new insights into the magnetic field driven assembly and reconfiguration of colloids and establish the principles of guiding local reactions within continuous media using pre-assembled microstructures. The fundamental principles developed in the project may provide a platform for rapid and robust assembly of colloidal structures with low, but controlled symmetry, which is difficult to achieve by conventional colloidal assembly techniques.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.