title: Solution properties of perfluorinated anionic surfactants with divalent counterion of separate electric charges.
abstract: Novel surfactants of perfluorinated double long-chain salts with divalent counterion of separate electric charge, 1,1-(1,omega-alkanediyl)bispyridinium diperfluorononanoate (CnBP(FC9)2, n = 2, 4, 6, 8) were newly synthesized. Their solution properties were investigated by surface tension measurement over the temperature range from 298.2 to 313.2 K, where magnesium diperfluorononanoate (Mg(FC9)2) was employed as a reference surfactant with divalent counterion of concentrated electric charge. From change of surface tension with concentration, the critical micelle concentration (CMC), surface excess (Gamma), apparent molecular surface area (A), and -log(concentration to reduce surface tension of water by 20 mN m-1) (pC20) were determined. The CMC values of CnBP(FC9)2 decreased with increasing charge separation and with increasing temperature, where the values of CnBP(FC9)2 were much smaller than those of Mg(FC9)2. In addition, the pC20 values of the former were also much larger than those of the latter. These results indicate a strong influence of the extent of charge separation or the spacer length of the counterions upon surface activity of the fluorinated surfactants. The surface excess or the corresponding apparent molecular surface area monotonously changed with the spacer length (n < or = 6), whereas the behavior for n = 8 was much different from the other CnBP(FC9)2 due to conformational change in the in-between alkanediyl chain. The entropy changes (Deltas) for the surface adsorption or condensation were found to be mostly negative for CnBP(FC9)2, where the changes approached zero with an increase in the charge separation. On the other hand, the changes for Mg(FC9)2 were positive over the whole concentration below the CMC. In addition, Brewster angle microscopy indicated no condensation of the present surfactants just at the air/solution interface.
authors.affiliation: Division of Biointerfacial Science, and Department of Chemo-Pharmaceutical Sciences, Graduate School of Pharmaceutical Sciences, Kyushu University, 3-1-1 Maidashi, Higashi-ku, Fukuoka 812-8582, Japan.
authors.forename: Jyunya
authors.initials: J
authors.lastname: Masuda
authors.forename: Hiromichi
authors.initials: H
authors.lastname: Nakahara
authors.forename: Satoru
authors.initials: S
authors.lastname: Karasawa
authors.forename: Yoshikiyo
authors.initials: Y
authors.lastname: Moroi
authors.forename: Osamu
authors.initials: O
authors.lastname: Shibata
mesh_terms: D000327:Adsorption; D000838:Anions / Q000737:chemistry; D004583:Electrons; D005461:Fluorine / Q000737:chemistry*; D008958:Models, Molecular; D015394:Molecular Structure; D012996:Solutions; D013499:Surface Properties; D013501:Surface-Active Agents / Q000737:chemistry*; D013696:Temperature
chemical_list: D000838:Anions; D012996:Solutions; D013501:Surface-Active Agents; D005461:Fluorine