Surface activity, salt and pH tolerance, and wettability of novel nonionic fluorinated surfactants with a short fluorocarbon chain

Fluorinated surfactants, especially those with long fluorocarbon chains (CxF2x+1, x > 7) like perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS), are used wildly in industrial and household fields. As research results have shown that such long fluorocarbon chain surfactants are seriously toxic, obviously persistent and highly bioaccumulative in the environment, it is an urgent requirement to develop novel alternatives of the long fluorocarbon chain surfactants. In this work, a series of novel nonionic fluorinated surfactants (FxCy-m) was synthesized by introducing an isophorone diisocyanate unit (as a spacer) between a short hydrophobic fluorocarbon chain (x ≤ 6) and a hydrophilic polyethylene glycol (PEG) chain with a facile two-step couple reaction using commercially available reagents. The chemical structures of FxCy-m were characterized by FT-IR and 1H NMR, and the relationships between length of hydrophilic/hydrophobic chains and surface activity of FxCy-m were systematically investigated by surface tension measurements. Among them, F6C2-400 with a longer fluorocarbon chain and a shorter PEG chain exhibits the highest surface activity, and its capability of reducing surface tension is almost equivalent to that of NaPFO (a derivative of PFOA). Meanwhile, F6C2-400 also has an excellent tolerance to salt and pH as well as an effective wettability. The facile preparation method and the clear structure-activity relationship in our research provide a valuable reference for development of nonionic surfactants with a short fluorocarbon chain.