(112g) Self-Assembly and Optical Properties of Colloidal Dispersions in Electromagnetic Fields

Self-Assembly and Optical Properties of Colloidal Dispersions in Electromagnetic Fields Professor James Swan represents the best of what a scientist and mentor can be, and I was incredibly fortunate to have Jim as my PhD advisor. I will always be grateful for the time Jim spent working closely with me, his incredible patience and skill when teaching difficult topics, and his genuine dedication to his students’ success in grad school and beyond. Knowing Jim has made me a much better scientist, educator, and person. As I continue my academic career path, I will always see Jim as a role model for the kind of scientist I wish to be. In this talk, I’ll discuss these experiences working with and learning from Jim, some projects we accomplished together, and promising current research inspired by my time with Jim.

Electromagnetic (EM) fields are useful for driving colloidal particles, offering experimentally facile strategies for controlling interparticle interactions, directing motion, and tuning material properties on-the-fly. Predictive, theoretical frameworks are needed for strategic engineering of field-driven colloidal materials used in optoelectronic devices, consumer products, and biomedical applications, but EM phenomena are notoriously hard to incorporate into colloidal models. Here, I will discuss theoretical and computational approaches for studying the assembly and optical properties of field-driven colloids. First, I discuss the field-directed self-assembly of polarizable colloids into colloidal crystals. I show that an important physical feature, many-bodied mutual polarization, whereby the dipole moment induced in one particle affects the dipole moments of surrounding particles, has a remarkably strong influence on the nature of the self-assembled states. Correctly accounting for mutual polarization enables a thermodynamic theory to compute the equilibrium phase diagram that agrees well with simulations and experiments. Though the equilibrium structures are crystalline, in practice, dispersions typically arrest in kinetically trapped, disordered or defective metastable states due to strong interparticle forces. I show that cyclically toggling the external field on and off over time leads to growth of colloidal crystals at significantly faster rates and with many fewer defects than for assembly in a steady field. The toggling protocol stabilizes phases that are only metastable in steady fields, including complex, transmutable crystal structures. If the particles comprising these and other self-assembled structures are metallic or semiconducting, they display plasmonic resonance at particular wavelengths of light. Mutual polarization among particles couples together these plasmonic resonances and results in structure-dependent optical properties. Using a combination of simulations and experiments, I describe the structure-property relations governing the plasmonic response of self-assembled colloidal materials.