MEASUREMENTS AND MODELS OF COLLOIDAL PARTICLE DYNAMICS AND ENERGY LANDSCAPES IN MAGNETIC FIELDS AND WITH ADDITIVES IN SOLUTION

Understanding colloidal interactions upon the application of external fields or the addition of secondary components has huge implications for engineering new particle-based materials and products. Electric or magnetic fields can control many particle collective dynamics and structures, leading to novel ordered materials, and can be used for studying nonequilibrium state behavior and for creating innovative active particle systems. Similarly, modulating particle-surface interactions in the presence of additives could enable the design of particles that favorably deposit onto a desired substrate for personal care products and drug delivery. In this dissertation, two different colloidal systems are studied and the dynamics and energies of both are fully characterized. For the first system, the fundamental phenomena influencing magnetic particle behavior in a rotating magnetic field were identified by matching simulations with video microscopy experimental data. In the second system, the mechanisms of core-shell microcapsule binding were characterized as a function of surfactant and polymer concentrations. Magnetic particle interactions and assembly in rotating magnetic fields were systematically quantified by first measuring single particle and doublet rotation and particle-particle separation across a frequency range for two different field amplitudes. Then, multiple particle assembly from a chain to a condensed structure was measured as a function of field amplitude and frequency. Stochastic models were also developed in parallel to match the one, two and multiple particle experimental observations and to unequivocally show how specific variables and physics in the model influence key features in the real system. The simulations were then used to further characterize the kinetics and thermodynamics by solving the one-dimensional Fokker-Planck (FP) equation for effective pair potentials for the two-particle system and an order-parameter FP equation to characterize the assembly process for multiple particle systems. The resulting diffusivity and effective energy landscapes illustrate how particle interactions, assembly pathways, and microstructures can be tuned by applied field conditions. Total Internal Reflection Microscopy (TIRM) was conducted on two different anionic microcapsules, as provided by an industry collaborator, to study how fragrance particle deposition onto human hair can be engineered under shampooing conditions. Experimental videos of the capsules interacting with a glass slide, which is negatively charged to mimic human hair, were analyzed as a function of increasing either amphiphilic surfactant or cationic polymer weight percent. Image analysis algorithms enabled us to capture particle trajectories in x, y and z, from which deposition lifetimes and potential energy profiles were calculated. The results revealed the various interactions that influence capsule deposition and will inform future work on how the capsules deposit in solutions with both surfactants and polymers