| dc.description.abstract | Novel surfactant/polyelectrolyte complexes have been the focus of recent research efforts due to their applications in consumer products, petroleum engineering and biotechnology. The interaction between surfactant and polyelectrolyte results in considerable system property change, such as foam stability, wettability and coating properties. Currently, most research efforts on this topic focus on the behavior of the complex system (including nanoparticles, free surfactants, dispersed surfactant and polyelectrolyte aggregates) with very few studies aimed at understanding the bulk properties and interfacial behavior of the self-assembled nanoparticles alone. In this dissertation, the bulk properties of refined polyethylenimine(PEI)/sodium dodecyl sulfate (SDS) nanoparticles with and without salts were first investigated. The self-assembly of positively charged nanoparticles had a narrow particle size distribution. Particle size, surface charge and the stability of the nanoparticle solution are controlled by pH, stock solution ratio as well as ionic strength. Additionally, in the presence of salts, both co-ions and counter-ions affected the stability of these refined colloidal particles. The observed results were different from the effect of salt on polyelectrolyte/surfactant mixtures where the salts interact with the individual compound not the particle as a whole. Moreover, the electrostatic interactions and solvation forces are important for the interaction between the salts and refined nanoparticles. To study the interfacial properties, surface tension measurements was employed as a first step to investigate the adsorption of PEI/SDS nanoparticles to the air/water interface. These results were correlated with the interfacial microrheology and microscopy data to study the details of the short and long term interfacial behavior of these surfactant-like particles. In this study, we discovered an interfacial induced disassembly of these refined nanoparticles. Such novel phenomena can lead to several potential applications. Also, adsorption of these refined nanoparticles at solid/liquid interface was investigated by means of quartz crystal microbalance with dissipation (QCM-D) and atomic force microscopy (AFM) techniques. First, it was found that gold surface with low charge density rendered loose binding between nanoparticles and gold surface allowing rearrangement of the adsorbed nanoparticles. Further, the negatively charged silicon dioxide had stronger electrostatic attraction with the positively charged nanoparticles, leading to tight binding of nanoparticles on the surface, it was then hard for the nanoparticles to rearrange themselves on the surface. | |
