Study On Responsive Emulsions And Surfactant Aggregates

Responsive emulsion is stable under certain condition, but becomes unstable by adding a trigger. In many cases, we need stable emulsion while in some cases require the emulsion to be break, such as crude oil transportation. Emulsion stability during transport is necessary inside a pipeline, once the crude oil is transported to its destination, emulsion stability is no longer desired. So do the oil sands separation, emulsion polymerization. Therefore, systematic study on responsive emulsion is of great significance.Preparation of responsive emulsion mainly uses switchable surfactants, the stimulus focus on pH and CO2. PH switchable surfactant stabilized emulsion can achieve demulsification just needs regulate the pH value. CO2 switchable surfactants are widely concerned because of its environment friendly and recycled advantages. Recently, preparation of pHresponsive emulsion uses surfactants that contain amine or carboxyl group. But we found that emulsions stabilized by sugar-based surfactants also have pH responsiveness. Preparation of CO2 responsive emulsion principally uses amidine-based switchable surfactants, which need complex synthesis. Here, we used a conventional surfactant for preparing CO2 responsive O/W emulsions by reaction with a switchable solvent and researched the phase behavior of surfactant and solvent. And then CO2 responsive microemulsion and short-chain fatty acids were used for oily cuttings cleaning. The present dissertation includes three topics:1. Preparation of pH responsive emulsion with sugar-based surfactantsSugar-based surfactants APG and Span 80 were used to prepare pH-responsive emulsions. We further studied the effect of surfactant ratio, concentration, oil-water ratio, temperature, NaCl concentration and the type of oil phase on the stability of emulsions. Demulsification was achieved at low pH and reemulsification was achieved at high pH. Zeta potential showed that emulsion droplets are high negatively charged under alkaline conditions. This means that there has high electrostatic repulsion between emulsion droplets. The electrostatic repulsion between emulsion droplets was sharply reduced by lowering the pH and demulsification was achieved rapidly.2.Preparation of CO2 responsive emulsion with switchable hydrophobic tertiary amineDMCHA was used as an oil additive to prepare CO2 responsive O/W emulsions with a conventional surfactant, sodium dodecyl benzene sulfonate(SDBS), as the emulsifier. Emulsions containing DMCHA in paraffin oil were more stable than those without DMCHA, as a result of electrostatic interactions between a small fraction of protonated DMCHA and SDBS, confirmed by surface tension and 1H NMR measurements. However, when exposed to CO2 most of the paraffin oil and water separate from the emulsion with formation of a middle phase microemulsion. More significantly, DMCHA could be separated from the lower water phase upon removal of CO2 and recycled.3.Phase transition in SDBS/DMCHA systems and study on oily cuttings cleaningA phase transition from micelle, La to a microemulsion takes place with increasing DMCHA content in the water/SDBS system. The DMCHA induced morphology change of SDBS aqueous solution was investigated by 2H NMR. The rheological measurements show the viscoelastic property of the La phase. Due to the CO2 switchability of DMCHA, a CO2 responsive microemulsion was prepared finally. Conductivity and pH measurements confirmed CO2 responsibility of the microemulsion. And then CO2 responsive microemulsion and short-chain fatty acids were used for oily cuttings cleaning.