Surface activity of a series of fluoroether betaine amphoteric surfactants: Oxygen roles

As PFOS, PFOA and their derivatives were banned according to the Stockholm Convention for their potential bioaccumulation and toxicity, people attempted to substitute the legacy fluorosurfactants with short-chain ones. Although short-chain alternatives can alleviate bioaccumulation, surface activity was compromised. Fluorine industry kept seeking for effective solution. In this work, we prepared and investigated a series of fluoroether betaine surfactants for their surface activity and spreading property. The role of oxygen on surface activity was discussed. We found that insertion of oxygen atoms into fluorinated chain could increase hydrophobicity and thus enhance surface activity. The contribution of one oxygen is approximately half of that of a difluoromethylene group by experience. Moreover, introducing oxygen diversified the structure to fill in the gap of surface activity between short and long fluorosurfactants. In summary, this work provided basic knowledge for molecular design. The surface activity of fluoroether betaine surfactants were characterized, including surface tension, critical micelle concentration, and spreading volume. Oxygen plays a role on increasing hydrophobicity of fluorosurfactants, which provide basic knowledge for molecular design of PFOA alternatives. [Display omitted]