Study on surface adsorption from cationic surfactant–electrolyte mixed aqueous solution including BF 4 − ion

• Published in: Colloid and polymer science Vol. 288; no. 9; pp. 1005 - 1011
• Main Authors: Imai, Yosuke, Shimamoto, Kei, Takiue, Takanori, Matsubara, Hiroki, Aratono, Makoto
• Format: Journal Article
• Language: English
• Published: 01.06.2010
• ISSN: 0303-402X; 1435-1536
• DOI: 10.1007/s00396-010-2221-y

The surface tension of aqueous mixtures of dodecyltrimethylammonium tetrafluoroborate (DTABF₄) and sodium tetrafluoroborate (NaBF₄) was measured as a function of total molality and composition of DTABF₄ at 298.15 K. The results were analyzed by originally developed thermodynamic equations and compared with those of dodecyltrimethylammonium bromide (DTAB)-sodium bromide (NaBr) mixed system. It was indicated that BF ₄ ions reduce the repulsion between DTA⁺ ions more effectively than Br ions in the adsorbed film. To investigate this difference more closely, the surface tension of DTAB-NaBF₄ and DTABF₄-NaBr mixed system was also measured. The data analysis revealed that BF ₄ ions are adsorbed positively even for the pure NaBF₄ system and preferentially to Br ions in these mixtures. Furthermore, it was concluded that the side-by-side arrangement suggested in the adsorbed film of 1-hexyl-3-methylimidazolium tetrafluoroborate (HMIMBF₄) is due to not only the positive adsorption of BF ₄ ions but also the capability of hydrogen bond formation between imidazolium ion and BF ₄ ions.