Programmable Matter: Control Over Material Behaviour Through Scalable Self Assembly

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Objects created today are primarily passive, i.e., they are unable to change their form or function after fabrication. One new approach to move beyond this severe limitation is to fabricate 3D objects embedded with functional artifacts that can change properties in response to external stimuli. Magnetostatic interactions among magnetic nanoparticles will be used to produce reversible self-assembled structures in a simpler and more flexible manner than available self-assembly methods. Starting from the same initial magnetic nanoparticle dispersion, variations in an externally applied magnetic field will provide a wide range of geometries that will be captured within composite materials after their surrounding liquid prepolymers are solidified. The different self-assembled microstructure geometries and their long-range organization will enable the design and fabrication of tunable bulk properties in these magnetic nanocomposites, such as their elastic moduli, magnetic susceptibility and remanance, and electrical and thermal conductivities. These properties will be correlated with specific microstructure assemblies, i.e., with the process control variables. This transformative approach will enable the design and fabrication of materials with a desired set of properties stipulated a priori. Theory, experiments and numerical simulations will all inform this investigation. This research will develop scaling laws correlating control variables to geometric features of self-assembled structures and validate them through experiments. Optical microscopy will be used for two-dimensional microscale imaging, X-Ray computed tomography for three-dimensional microscale imaging and transmission electron microscopy for nanoscale imaging. Numerical simulations will use Brownian dynamics providing Lagrangian tracking of individual particles coupled with magnetization dynamics using the Landau-Lifshitz-Gilbert equations to extend the investigation beyond experimental limits. The influence of microstructure on mechanical properties such as elastic moduli will be measured using atomic force microscopy in force volume mode and nanoindentation to record microscale heterogeneities, and tensile tests for determining its influence on bulk elastic moduli and anisotropy. Predictions of remanance will be validated by magnetic force microscopy and spin-polarized electron microscopy. Bulk magnetic properties will be determined using vibrating sample magnetometry. This research will enable design of the microstructure geometry to produce specific bulk material properties. It promises transformational applications spanning multiple disciplines, e.g., medicine (scaffolding methods in tissue engineering and intracellular actuators), device fabrication (MEMS and spintronics devices), and smart surfaces with tunable asperities (for lab-on-chip-devices and droplet-based microfluidics). We will involve four HQP, i.e., two Ph.D. students, an undergraduate student and a postdoctoral researcher, to perform interdisciplinary research spanning magnetics, mechanics, soft materials, nanoscience, and transport phenomena using mathematical modeling, experiments and numerical simulations.