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Thesis
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CO2-Switchable Foaming Agents

Authors: Poole, Hailey;

CO2-Switchable Foaming Agents

Abstract

The work presented in this thesis focuses on expanding the use of CO2-triggered switchable surfactants for switchable foam stability. Three CO2-responsive switchable cationic surfactants (SCS) with switchable heads were first explored namely, two acetamidines and one dimethylalkylamine. Acetamidine surfactants were found to be inappropriate for foam studies as they hydrolyze when added to water. However, it was possible to study the foam properties of N,N-dimethyltetradecylamine (C14DMA) in the presence and absence of CO2. In the absence of CO2, C14DMA is a water insoluble organic molecule unable to generate foam. In the presence of CO2, the dimethylalkylamine head group becomes protonated and transforms C14DMA into a cationic surfactant that is able to generate foam with moderate stability. Note that the use of CO2 as the dispersed gas always leads to unstable foams due to its high solubility in water resulting in fast coarsening. More stable foams are thus generated with the protonated surfactant and a less soluble gas such as N2. However, continuous N2 dispersion eventually displaces the CO2 in the solution thus deprotonating and “deactivating” the surfactant. Therefore a new class of CO2-switchable surfactants were synthesized to stabilize foams in the presence of an inert gas, such as N2, and prevent foam generation in the presence of CO2. This new class is called CO2-responsive cationic tail switchable surfactants (STSs). These surfactants have a typical polar head group (either cationic, anionic, or non-ionic) while the CO2-responsive group is placed in the middle of the hydrocarbon tail. With aqueous solutions of these molecules one can generate foam with N2. In the presence of CO2, the trialkylamine becomes protonated and disrupts the amphiphilic nature of the surfactant molecules, thus eliminating or decreasing the surfactants ability to produce foam. The STSs synthesized and investigated in this thesis were 5-(heptyl(methyl)amino)-N,N,N-trimethylpentan-1-aminium bromide (C12N(Me)TAB), sodium 4-(methyl(octyl)amino)butane-1-sulfonate (C12N(Me)SSn), and 8-(butyl(methyl)amino)octyl-myo-inositol (C12N(Me)I). To understand the foaming properties of these surfactants, the time evolution and the structure (liquid fraction, bubble size, and bubble size distribution) of the foams generated were studied.

Country
Canada
Related Organizations
Keywords

CO2 switchable surfactants, Foam

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