| Description |
This dissertation describes the preparation and properties of nanoporous membranes made using surface-functionalized silica nanoparticles. Nanoporous membranes can be used in nanofiltration, or separation of various nanoscale and molecular entities - from proteins and nanoparticles to salts. Membranes aid in separation of mixtures while providing high efficiency and low cost, and I tailored the specific properties of these membranes by adding polymer brushes to the surface of the silica nanoparticles and varying their composition. Chapter 1 provides the necessary background information on fabrication and design of nanoporous materials, preparation of surface-functionalized nanoparticles, and relevant polymer physics. Chapter 2 describes the preparation of membranes using nanoparticles decorated with polyelectrolyte copolymer brushes (poly[(3-sulfopropyl methacrylate)-co-(2-ethoxyethyl methacrylate)] (PSPM-co-PEEMA)). I studied the effect of polymer length and charge on the rejection of charged species and the pore size. I found that there are multiple ways the polymer brushes can interact with each other which strongly affects the effective surface charge and the pore size of the corresponding membranes. Chapter 3 discusses the preparation of temperature-responsive membranes using nanoparticles carrying (poly(N-isopropylacrylamide) (PNIPAM)) polymer brushes. Membrane water permeability measurements at different temperatures unveiled that the polymer response nonlinearly depends on the polymer length. Chapter 4 describes the preparation and properties of membranes from nanoparticles carrying pH-responsive polymer brushes (poly-(dimethylaminoethyl methacrylate) (PDMAEMA)). I looked into the membrane response to pH and solvent polarity and discovered that polymer length has no effect on permeation in "good" solvents but changes dramatically for "bad" solvents. Chapter 5 summarizes the findings of this work and suggests future directions. |
