Synthesis, Characterization, Adsorption, and Interfacial Rheological Properties of Four-Arm Anionic Fluorosurfactants

• Published in: Langmuir Vol. 24; no. 6; pp. 2412 - 2420
• Main Authors: Ertekin, Ayça, Kausch, Charles M, Kim, Yongsin, Thomas, Richard R
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 18.03.2008
• Subjects: Adsorption; Anions - chemical synthesis; Anions - chemistry; Catalysis; Chemistry; Colloidal state and disperse state; Exact sciences and technology; General and physical chemistry; Hydrocarbons, Fluorinated - chemical synthesis; Hydrocarbons, Fluorinated - chemistry; Micelles. Thin films; Molecular Structure; Rheology; Surface physical chemistry; Surface Tension; Surface-Active Agents - chemical synthesis; Surface-Active Agents - chemistry; Theory of reactions, general kinetics. Catalysis. Nomenclature, chemical documentation, computer chemistry; Ring opening polymerization; Hydrophobicity; Characterization; Relaxation; Micellar critical concentration; Synthesis; pH; Polyol; Diffusion coefficient; Monomer; Transport equation; Chain length; Saturation; Fluorine compound; Buffer solution; Ammonium hydroxide; Dynamic surface tension; Ammonium sulfate; Adsorption; Isotherm; Surface tension; Transport; Physicochemical properties; Catalyst; Neutralization; Rheological properties
• ISSN: 0743-7463; 1520-5827
• DOI: 10.1021/la7031175

Four-arm oligo(fluorooxetane) tetraols containing −CF3 and −C2F5 groups were prepared in reasonable yields by cationic, ring-opening polymerization of fluorinated oxetane monomers using a tetrafunctional, alkoxylated polyol as initiator and BF3·THF as catalyst. The tetraols were then converted to ammonium sulfate salts using oleum followed by neutralization with ammonium hydroxide in excellent yields. The four-arm oligo(fluorooxetane) sulfates (1 = −CF3, 2 = −C2F5) have an architecture characterized by a hydrophobic core of oligo(fluorooxetane) arms with a hydrophilic sulfate shell and initiator. The four-arm anionic oligo(fluorooxetane)s are surface active with critical micelle concentration values ≈4.2 × 10-6 and 2.4 × 10-6 mol/L for 1 and 2, respectively. Surface tension isotherms in pH 8 buffered solution were measured and data fitted parametrically to the Davies surface tension isotherm equation. Molecular areas at saturation were estimated to be ∼89 and ∼85 Å2 with ΔG ads = −12.7 and −13.2 kcal/mol for 1 and 2, respectively. The results are compared to two-arm, bolaamphiphilic analogues of 1 and 2 and a small molecule, long perfluoroalkyl-chain (−C8F17), anionic fluorosurfactant (Kausch, C. M.; Kim, Y.; Russell, V. M.; Medsker, R. E.; Thomas, R. R. Langmuir 2003, 19, 7182). Dynamic surface tension data for 1 and 2 were analyzed using the Ward−Tordai mass transport equation to yield concentration-dependent diffusion coefficients. In the concentration range ≈10-6 mol/L, diffusion coefficients were estimated to be ≈1 − 3 × 10-5 cm2/s. Dilational interfacial rheological parameters for 1 and 2 were measured. Values of |E| and E‘ were found to be larger than those of the two-arm analogues of the same perfluoroalkyl chain length while E‘ ‘and φ were found to be smaller. The magnitude of these values reflects the difference in adsorption strength and mass transport and/or relaxation between the two different architectures.