Relationships between structure and dynamics in fluids have a wide variety of applications. Because theories for fluid structure are now well developed, such relationships can be used to “predict” dynamic properties. Also, recasting dynamic properties in terms of structure may provide new insights. In this thesis, we explore whether some of the relationships between structure and dynamics that have proven useful for understanding simple atomic liquids can also be applied to complex fluid systems. In particular, we focus on model fluid systems with particles that interact with attractive forces that are shortranged (relative to the particle diameter), and display properties that are anomalous when compared to those of simple liquids. Examples of fluids with short-range attractive (SRA) interactions include colloidal suspensions and solutions of micelles or proteins. We show via simulations that common assumptions regarding free volume and dynamics do not apply for SRA fluids, and propose a revision to the traditional free volume perspective of dynamics. We also develop a model which can predict the free volume behavior for hard-sphere and SRA fluids. Next, we demonstrate that the dynamic properties of SRA fluids can be related to structural order. In terms of structural order, the properties of SRA fluids can be related to those of another anomalous fluid, liquid water. In both fluids, anomalous dynamics are closely related to anomalous structure, which can be traced to changes in second and higher coordination shells. We also find that a similar relationship between structural order and dynamics approximately holds for fluids under shear. Motivated by previous work, we explore via simulation how tuning the particle-wall interactions to flatten or enhance the particle layering in a confined fluid impacts its self-diffusivity, viscosity, and entropy. We find that the excess entropy explains the observed trends. Finally, we present preliminary simulation data regarding the relationship between heterogeneous dynamics and structure. We show that the mobility of particles is related in a simple way to the structure of the particles surrounding them. In particular, our results suggest that a critical amount of local disorder allows a particle to be mobile on intermediate time scales. / text

Suspension flows in varied settings and at different concentrations of particles are studied theoretically using various modeling techniques. Particulate suspension flows are dispersion of particles in a continuous medium and their properties are a consequence of the interplay among hydrodynamic, buoyancy, interparticle and Brownian forces. The applicability of continuum modeling techniques to suspension flows at different particle concentration was assessed by studying systems at different time and length scales. The first two studies involve the use of modeling techniques that are valid in systems where the forces between particles are negligible, which is the case in dilute suspension flows. In the first study, the growth and progradation of deltaic geologic bodies from the sedimentation of particles from dilute turbidity currents is modeled using the shallow water equations or vertically averaged equations of motions coupled with a particle conservation equation. The shallow water model provides a basis for extracting grain size and depositional history information from seismic data. Next, the Navier-Stokes equations of motion and the convection-diffusion equation are used to model suspension flow in a biomedical application involving the flow and reaction of drug laden nanovectors in arteries. Results from this study are then used prescribe the best design parameters for optimal nanovector uptake at the desired sites within an artery. The third study involves the use of macroscopic two phase models to describe concentrated suspension flows where interparticle hydrodynamic forces cannot be neglected. The isotropic form of both the diffusion-flux and the suspension balance models are solved for a buoyant bidisperse pressure-driven flow system. The model predictions are found to compare fairly well with experimental results obtained previously in our laboratory. Finally, the power of discrete type models in connecting macroscopic observations to structural details is demonstrated by studying a system of aggregating colloidal particles via Brownian dynamics. The results from the simulations match experimental shear rheology and also provide a structural explanation for the observed macroscopic behavior of aging. / text