Nanoparticle agglomeration and assembly in confined spaces

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We propose to study the agglomeration of colloidal particles in confinement by means of experiments and simulations with the aim to design specific composites.The basic experimental method has already been established in the group in Saarbrücken: Particles with diameters of around 10 nm are introduced into the dispersed phase of an emulsion, which is then slowly evaporated. Appropriate surfactants prevent the formation of Pickering emulsions and force the particles to remain inside the droplets. Under these conditions, the particles' behavior is reminiscent of metal atoms. They form minimum-energy "Lennard-Jones" clusters, supraparticles with predictable geometries. The process is a technologically promising route to well-defined microstructures and an excellent experimental platform to study and tune agglomeration.In the project proposed here, we want to establish a theoretical understanding of ordered agglomeration in confinement and extend the process to technologically relevant particle mixtures. Mixtures of nanoparticles will be assembled inside emulsions. Depending on the particles' interactions and the process kinetics, the particles in the droplets may phase-separate into "Janus" supraparticles, assemble into regular binary crystals that lead to "patchy" supraparticles or form disordered "mixed" supraparticles. We propose to analyze the assembly process by means of simulation at the single particle level. To predict which particles, ligands and process conditions can yield which morphology, we will perform simulations where particle interactions and confining geometries will be systematically varied.The simulations will be carried out at the university of Luxembourg. The problem of finding optimal binary Lennard Jones clusters under confining boundary conditions will be addressed by means of a basin hopping approach. Once the minimum potential energy configurations will have been found, we will also address their thermal stability using a method to calculate free energies that we have recently developed. At INM, we will select particle mixtures and process conditions according to the simulation results and assess experimentally whether the predicted structures form. Metal and oxide nanoparticles will be mixed, emulsified, and assembled into supraparticles. The assembly will be observed in situ through time-resolved optical transmission spectroscopy and light scattering. Electron microscopy will yield real-space structures of the particles, light scattering and x-ray spectroscopy will inform us whether the structures are homogeneous and stable. If we succeed in creating Janus clusters from particles of different polarity, we will analyze their behavior as surfactants.