(256e) Structural Development during Emulsion Assembly of Binary Particle Mixtures: Simulation and Experiment

Self-assembly of nanoparticles at fluid-fluid interfaces is a promising route to produce precisely controlled functional materials. Recently, a water-in-octanol reverse emulsion process was developed to prepare micron-sized optically-active spherical supraparticles (supraballs) composed of ~200 nm synthetic melanin nanoparticles [Xiao et al. Sci. Adv. 2017, 3 (9), e1701151]. In this talk, we present our recent work combining experiments and coarse-grained molecular dynamics (CG-MD) simulations to explore this supraball assembly process using binary mixtures of melanin and silica particles. We probe mixtures with varying particle size and surface chemistry to provide additional tunability to the supraball structure, including the relative fraction of melanin vs. silica particles at the surface of the supraballs (the dominant contributor to the supraballs’ optical response), as well as particle packing/mixing/demixing within the supraball interior (important for the potential use of these supraballs as porous catalysts or drug delivery materials). Computationally, we parameterize a CG model for particle-particle and particle-interface interactions by incorporating information from experimental microscopy, interfacial tension, and particle-interface contact angle techniques, then mimic the emulsion assembly process by performing CG-MD simulations of particles in progressively shrinking spherical confinement. We find that melanin-based particles are strongly enriched at the surface of the supraballs, and we demonstrate that differences in the contact angles of the particles at the liquid-liquid interface during emulsion assembly drives the segregation of melanin particles to the supraball surface. We also discuss the calculation of small-angle scattering patterns from simulations to characterize particle mixing/demixing within the supraball interior.