Critical Micelle Concentrations and Partial Molar Volumes for Perfluoroalkanoates Salts in Aqueous Solutions

Abstract

Determination was made of critical micelle concentrations (cmc) for four homologs of perfluoroalkanoate salts, C_nF_2n+1COOLi (n=510), C_nF_2n+1COONa (n=58), C_nF_2n+1 COOMe₄N (n=510), and C_nF_2n+1COOEt₄N (n=410), in aqueous solution at 25°C. The results were expressed as, log cmc=A+Bn. B values were -0.445-0.463, indicating cmc to decrease by 2.82.9 for each CF₂ group added to the perfluoroalkyl chain. The effects of counter ions on cmc for C₇F₁₅COO^-M⁺ (M=Li, Na, K) were examined at 35°C. It was found that cmc decreased in the order of Li>Na>K. Limiting partial molar volumes (V⁰) for C_nF_2n+1COOMe₄N (n=16) in water were measured at 25°C.V⁰ values increased with the number of carbon atoms ; the increment per CF₂ group was 23.7 cm³·mol^-1 on the average.