Perfluoroalkylated poly(oxyethylene) thiols: Synthesis, adsorption dynamics and surface activity at the air/water interface, and bubble stabilization behaviour

• New amphiphiles with a poly(oxyethylene) spacer inserted between a thiol function and a F-alkylated chain have been synthesized.
• The F-alkylated POE thiols adsorb rapidly at the air/water interface.
• They decrease the interfacial tension of water to values as low as ∼16 mN m−1.
• They form microbubbles in aqueous solutions with diameters smaller than 10 μm.
• The microbubbles were stable for days when a fluorocarbon gas is present in their gas phase.

We report the synthesis of four new perfluoroalkylated thiols, CnF2n+1(CH2)2(OCH2CH2)ySH (FnH2(OE)y with n = 4 and 6; y = 4 and 6, that have a hydrophilic poly(oxyethylene) (POE) segment inserted between the hydrophobic fluorinated chain and the thiol functional group. The dynamics of adsorption and surface activity of these compounds at the air/water interface were studied using bubble profile analysis tensiometry. The adsorption kinetics profiles show that all compounds diffuse rapidly to the air/water interface and decrease the interfacial tension of water to values ranging from 16.5 to 31.6 mN m−1, which qualifies them as potential components of microbubble shells. Their ability to self-assemble and stabilize gaseous microbubbles in the presence or absence of a fluorocarbon gas (perfluorohexane) was investigated by optical microscopy. Three out of the four compounds (the two F6 derivatives and F4H2(OE)6) were able to form and stabilize microbubbles. Microbubbles based on both F6 PEG thiols are more stable than those based on the F4 derivative. The number of oxyethylene (OE) groups substantially influences bubble stability; the higher the number of OEs, the more stable the microbubbles. Finally, the most important stabilising effect was obtained by introducing an internal fluorocarbon gas, whose presence in the bubble increases bubble stability from 6 h to 5 days for the most promising candidate, F6H2(OE)6SH.

New amphiphiles with a poly(oxyethylene) spacer inserted between a thiol function and a F-alkylated chain have been synthesized. The F-alkylated POE thiols adsorb rapidly at the air/water interface and decrease the tension of water to values as low as ∼16 mN m−1. They form microbubbles in aqueous solutions with diameters smaller than 10 μm. These microbubbles were stable for days when a fluorocarbon gas is present in their gas phase.Figure optionsDownload as PowerPoint slide