Facile synthesis and marked pH-responsive behavior of novel foaming agents based on amide- and ester-linked morpholine fluorosurfactants

There is an increasing demand to solve the environmental dissemination problems of fluorosurfactants and improve their responsive behavior, surface properties, chemical stability and foaming performance. In this work, three pH-responsive fluorosurfactants, named F-9-es-mor, F-9-N-3-mor and F-9-N-2-mor, were synthesized by facile one-step esterification or amidation. The F-9-N-2-mor efficiently reduced the water surface tension to 14.56 mN.m(-1) with a low critical micelle concentration (CMC) of 0.20 mM. More importantly, both F-9-N-2-mor and F-9-N-3-mor obviously displayed reproducible pH-response foaming behaviors at an optimal pH of 6.0 and 8.0, respectively, probably owing to their rigid molecular structure, strong intermolecular H-bond and high membrane elasticity. Besides, the morpholine fluorosurfactants defoam at pH below 4.0, indicating that these fluorosurfactants could be recycled and their residue could be easily removed. Overall, the novel fluorosurfactants F-9-N-2-mor might provide new inspiration to recycle fluorosurfactants as well as construct pH-responsive foams. (C) 2021 Elsevier B.V. All rights reserved.

Automated summary

Three pH-responsive fluorosurfactants were synthesized in this study, with F-9-N-2-mor efficiently reducing water surface tension at a low critical micelle concentration and showing reproducible foaming behavior at specific pH values. Moreover, the morpholine fluorosurfactants defoam in low pH environments, aiding in recycling efforts.