UC Berkeley

Nature utilizes amphiphilic assemblies to compartmentalize different chemical environments, modulate interfacial properties and reaction rates, and create complex materials with mesoscopic order. Many models explain the phase behavior of amphiphiles, but our understanding of the non-equilibrium behaviors of amphiphilic assemblies is limited. There exists a vast and rich space of structural and functional variations unexplored by equilibrium methods and models. A recent set of amphiphilic self-assembly experiments have suggested that non-equilibrium pathways of amphiphilic assemblies are complex and poorly understood\cite{Griffith2014}. In the experiments, assembly of 2-oxooctanoic acid was photoinitiated and eventually yielded monodisperse aggregates of long-term stability. In this dissertation, I explore various states of amphiphilic assemblies and the non-equilibrium processes that interconnect these states in the context of the photoinitiated assembly model system. In Chapter 2, I used molecular dynamics simulations to study structural variations and mechanisms of formation of the early nuclei from aqueous solution. Importance sampling and classical nucleation theory were employed to estimate the rate of nucleation. I found that the kinetics of coaggregation, where a mixture of more than one amphiphilic species, could differ significantly from that of single-species aggregation. Specifically, the participation of a second species could open up new pathways of growth and introduce microscopic phase separation of the two species within the aggregates and as a result modulate the growth rates. In Chapter 3, I computed the solutions to master-equation chemical kinetic models of amphiphilic aggregation pathways. I found that a large critical nucleus size is an important factor that contributes to the production of a narrow aggregate size distribution, a highly desirable characteristic in the preparation of self-assembled nanoparticles. I incorporate the elementary steps of nucleation, growth, and a source of precursor molecules to observe the effects of competing elementary rates on the aggregate size distribution. In Chapter 4, I furthered the development of the charge-frustrated Ising model to represent amphiphilic species with non-zero spontaneous curvatures. I also built in the correct interfacial roughness by using two lattice spacings in the same lattice model.