| Emulsions are metastable colloidal dispersion systems, which are widely used in a variety of applications including painting, cosmetics manufacturing, food processing and petroleum recovery. Surfactants are designed for adsorbing on the interface of oil/water to stabilize emulsions. However, they become the liability of the subsequent phase separation processes. Therefore, switchable surfactants with controllable surface active attract much attention. Switchable surfactants are molecules that exhibit surface active characteristics under one condition and become surface inactive upon changing the system conditions. CO2-switchable surfactants have caught attentions due to their moderate and efficient controllable properties. However, CO2-switchable surfactants are often expensive, and the synthesis processes are complicated.Superamphiphiles are a class of amphiphiles formed by non-covalent interactions, so the sophisticated synthetic processes of covalent compounds are avoided. Because of the controllable and reversible behaviors of non-covalent interaction, the self-assembly and disassembly of the superamphiphiles can be controlled by external stimuli. The self-assembly and aggregate structures of superamphiphiles are the main focuses in the literature. Little attention has been paid to emulsification behavior of superamphiphiles. As a kind of non-covalent interaction, electrostatic interaction is widely studied. The influence of organic cations on the anion surfactant systems is different to that of inorganic cations due to the speciality of molecular size and structure. However, attentions are paid on the influence on micelle structures and demulsification.Therefore, in this thesis, we assembled a CO2 switchable superamphiphile via electrostatic interaction. The structure and properties of superamphiphile were studied systematically, excepting their applications on reversible emulsification and demulsification processes. On the basis of electrostatic interaction and CO2 responsive properties, we also studied the influence of organic cation on emulsions stabilized by surfactants. The whole paper contains two sections:Section I:The highly CO2 responsive superamphiphile (D-OA) was assembled by fatty acid and Jeffamine D230. To confirm the possibility to be used as emulsifiers, the structure and properties of D-OA were studied. The results indicated that D-OA was assembled via proton transfer process. D 230 served both as counter-ion and the spacer in the superamphiphile D-OA system. Therefore, similar to gemini surfactant, D-OA possesses high solubility in water, low cmc and high interfacial activity. Bubbling CO2 into D-OA solution, phase-seperation occurred, while removing CO2 by N2, the solution returned back to its original state. This reversible transition is attributed to the reversible assembly and disassembly of D-OA according to the results of conductivity, pH and FT-IR. As D-OA was used as an emulsifier to stabilize emulsions, they could stay stable and destable state upon adding or removing CO2. The results of rapid response rate and complete demulsification provide guidance in demulsification and smart responsive materials.Section â…¡:Triethanolamine was used as the CO2 responsive materials to study the influence of its protonation state on emulsions. In the presence of CO2 and water, triethanolamine became quaternary ammonium salt, transforming the coarse emulsion stabilized by SDS/Span 80 to nanoemulsion. Mechansims of nanoemulsion formation was interpreted according to the results of interfacial tension, conductivity and rheological experiment. The results indicated that during the process of bubbling CO2, the IFT between oil and water reached ultralow value accompanied by phase transformation and an increase in interfacial curvature, leading to the formation of nanoemulsions. At a fixed surfactant concentration, emulsion composition had little effect on the droplet size and polydispersity. The formation of nanoemulsions provides a new thought to prepare nanoemulsions. |
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