Effective and efficient surfactant for CO2 having only short fluorocarbon chains

Area of Science:

• Supramolecular Chemistry
• Green Chemistry
• Materials Science

Background:

• Supercritical carbon dioxide (scCO2) is an environmentally friendly solvent with tunable properties.
• Microemulsions in scCO2 are crucial for various applications, but require efficient CO2-philic surfactants.
• Previous research identified fluorinated sulfogulutarate surfactants as effective solubilizers for water in scCO2.

Purpose of the Study:

• To develop more economical CO2-philic surfactants with enhanced solubilizing power and faster solubilization rates.
• To investigate the impact of fluorocarbon chain length and linking group on surfactant performance in W/CO2 microemulsions.
• To identify optimal surfactant structures for efficient water solubilization in supercritical CO2.

Main Methods:

• Synthesis and characterization of novel fluorinated bis(perfluoroalkyloxy)alkane sulfonates (nFG(EO)(2) and nFS(EO)(2)) with varying fluorocarbon chain lengths (n=4, 6, 8).
• Preparation and visual observation of water-in-supercritical CO2 (W/CO2) microemulsions.
• UV-vis spectral measurements using methyl orange as a reporter dye to determine the maximum water-to-surfactant molar ratio (W(0)).

Main Results:

• Microemulsions formed with nFG(EO)(2) surfactants exhibited W(0) values ranging from 60-80, while nFS(EO)(2) surfactants showed W(0) values of 40-50.
• The shortest fluorinated surfactant, 4FG(EO)(2), unexpectedly achieved the highest W(0) of 80, forming a transparent single-phase microemulsion.
• 4FG(EO)(2) demonstrated remarkably rapid solubilization of water into scCO2, even at high W(0) values (~80).

Conclusions:

• Fluorocarbon chain length significantly influences the solubilizing power and formation of W/CO2 microemulsions.
• Shorter fluorocarbon chains, contrary to expectations, can lead to superior performance in terms of water solubilization capacity and rate.
• The 4FG(EO)(2) surfactant presents a promising, cost-effective alternative for creating stable and efficient water-in-supercritical CO2 microemulsions.