Critical Micelle Concentrations of Perfluoroalkanesulfonate Salts in Aqueous Solution

Abstract

Determination was made of critical micelle concentrations (cmc) for three ho-mologs of perfluoroalkanesulfonate salts, C_nF_2n+1SO₃Li (n=4, 6, 8, 10), C_nF_2n+1SO₃Me₄N (n=4, 6, 8, 10), and C_nF_2n+1SO₃Et₄N (n=4, 6, 8) in aqueous solutions at 25°C, and the results are expressed in the form, log cmc=A+Bn. B values are -0.435-0.465, indicating cmc to decrease by 2.72.9 for each CF₂ group added to perfluoroalkyl chain. Due to the high Krafft points of sodium and potassium salts, the influence of counterions on cmc for C₆H₁₃SO₃^-M⁺ (M=Li, Na, K, Me₄N, and Et₄N) was examined at 65°C. It was found that cmc decreased in the order of Li> Na> K> Me₄N> Et₄N, and this order is discussed on the basis of ionic hydration of alkali metal ions and the hydrophobic interactions of quaternary ammonium ions with micelles.