Synthesis and surface properties of semi-fluorinated gemini surfactants with two reactive bromo pendant groups

This paper presents a series of semi-fluorinated gemini surfactants with two bromo pendant groups. It reviews the effect of the number of methylene units in the spacer group between the two hydrophilic quaternary ammonium heads. Critical micelle concentration (cmc) and free energy of micellization (ΔGM0) of the title surfactants, in aqueous solution, have been investigated as a function of the number n of carbon atoms in the hydrocarbon spacer. We have pointed out a different behaviour as compared to Gemini hydrocarbon homologues.In the present study, when the number of methylene units (n) in the spacer increases, the cmc first decreases and reaches an optimum for (n = 6), then it increases linearly from n ⩾ 6. Variations of cmc have been interpreted in terms of conformation changes of the surfactant ion and progressive penetration of the alkyl chain spacer in the micelle hydrophobic core. In this series, the increase of the hydrophobicity seems not to favour the micellisation process as expected, probably impacted by the mutual phobicity of the perfluorinated tails and the hydrocarbon spacer. A minimum is reached for a spacer with six methylene units which seems to be the optimal conformation. The free energy of micellization (ΔGM0) confirm this tendency.

Graphical abstractNovel class of semi-fluorinated cationic gemini surfactants with two bromo anchorage groups.Figure optionsDownload full-size imageDownload high-quality image (36 K)Download as PowerPoint slideResearch highlights► Hybrid surfactants were synthesized in five steps from perfluoroethyl iodides. ► These gemini surfactants can be precursors of non leaching biocidal surfaces. ► They showed a singular behaviour as compare to hydrocarbon homologues. ► Increasing the hydrocarbon spacer length destabilize the micelle oleophobic core.