Morphology of particle deposits
Tarabara, Volodymyr Valentinovich
Wiesner, Mark R.
Doctor of Philosophy
The premise that the structure of particle deposits can be predicted based on the knowledge of particle hydrodynamics, solution chemistry and surface chemistry of particles is explored in the framework of three environmental application areas: membrane filtration, in situ capping of contaminated sediments, and environmental sensing. The role of deposit morphology in membrane filtration was evaluated in bench-scale filtration experiments. Results from experiments were compared with theoretical expectations based on a mathematical model for permeate flux for limiting cases of dominant membrane and filter cake resistances. Microscopic examination of membrane cake cross-sections revealed a stratified structure and underscored the importance of coupling between hydrodynamic conditions and interparticle interactions for the permeate flux performance. The influence of suspension heterogeneity on the membrane cake structure was investigated in simulations of particle deposition. Particle Peclet number and collision efficiency were related to trends in colloidal deposit morphology as a function of particle transport and surface chemistry. The simulations identified potential limitations in modeling filter cakes as homogeneous material when suspensions are composed of several chemically distinct particulate fractions. The relationship between sediment cap morphology and transport characteristics across the cap were explored. Bentonite-cement composite is proposed as a new material for in situ capping of contaminated underwater sediments. In addition to being mechanically stable, such composites provide for a possibility to control cap microstructure through the fine-tuning of postdepositional hydration processes in the cap. Cement content and liquid-to-solid fraction were identified as two dominant factors that determine overall cap performance. Microscopic studies of composite structure, strength testing as well as numerical and laboratory modeling of diffusion across composite caps were used to establish formation-structure-performance links for the composites. Finally, the impact of variable deposit morphology on the efficiency of surface-enhanced Raman substrates was investigated. Ionic strength mediated silver nanoparticle deposition was explored as a route for the morphological design of optically active substrates for water quality monitoring. The critical dependence of the effect of surface-enhanced Raman scattering on the morphology of enhancing substrate was quantified as a basis for developing sensors with tunable sensitivity. Fractal analysis was used to quantify deposit morphologies and to correlate these to enhancement factors afforded by the substrates.
Environmental science; Environmental engineering