Cationic and Anionic Carbon Dioxide Responsive Switchable Surfactants
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Tail modified amidine type cationic switchable surfactants were synthesized. The modified structures included ethylene oxide units in the tail to increase water solubility. Surfactants with different hydrophile-lipophilic balance were available by virtue of the commercial availability of the alcohol precursors. Low viscosity emulsions of heavy crude oil were generated by activating indigenous crude oil surfactants with a water-soluble base. The emulsions containing approximately 70 wt% heavy crude oil were visually stable under ambient conditions for two weeks. Immediate phase separation was found to occur with the addition of carbon dioxide gas. Free water was easily separated from high viscosity crude oil. Improvements in the quality of phase separation were possible with water-soluble organic bases. Amidine surfactants with appropriate structure were also capable of stabilizing heavy crude oil emulsions. Anionic switchable surfactants were developed. The surfactants reacted with carbon dioxide to cause changes to interfacial properties. Carbon dioxide in aqueous solution was able to neutralize the anionic form of the surfactant. Examples include carboxylic acids and phenols. Heating and removal of carbon dioxide was, in most cases, sufficient to cause the surfactant to become anionic again. Interfacial properties such as surface tension and emulsion stability were controlled using the anionic switchable surfactant system. Otherwise stable emulsions were triggered to separate by addition of carbon dioxide. Polystyrene particles of 30 nm to 40 nm in diameter were made by emulsion polymerization using anionic switchable surfactants. The latex was stabilized by electrostatic charges with measured zeta potential below –30 mV. Treating the latex with carbon dioxide was found to cause aggregation of polymer particles. The aggregates were much larger with diameter of approximately 100 μm and readily separated by flotation and dried into a fine free flowing powder. Re-dispersion of the aggregates was possible after heating and mixing the slurry in water. The re-dispersed latex was found to be stabilized by electrostatic charges with measured zeta potential below –30 mV.