Langmuir 1992,8, 2344-2346
2344
The Partitioning of Pyrene-3-carboxaldehyde at the Micelle/Bulk Interface Estimated by the Fluorescence Method Koji Tamori, Yoshiaki Watanabe, and Kunio Esumi' Department of Applied Chemistry and Institute of Colloid and Interface Science, Science University of Tokyo, Kagurazaka, Shinjuku-ku, Tokyo 162, Japan Received March 2,1992. I n Final Form: June 18,1992
Introduction Micelles solubilize many kinds of materials and a partition coefficient of the solute between the micellar phase and bulk is available when a micelle is regarded as a phaseel In the case of alcoholas a solute, e.g., the partition coefficient can be calculated from the concentration of the alcohol in gas phase equilibrated with the micellar solution. The measurement is, however, not always easy. Pyrene-3-carboxaldehyde (PCA),whose maximum fluorescence wavelength, A, is highly correlated with solvent dielectric constant, is one of the most useful probes; X in a sufficiently concentrated surfactant solution serves as a measure of the polarity at the micelle/bulk interface.2 In the present study, a brief method to obtain the partition coefficient of PCA, PPCA,from measuring X at several surfactant concentrationswill be presented. Moreover, PPCAwill be determined for many kinds of surfactants, and the properties of the Surfactants will be discussed.
Figure Typical fluorescence spectra of PCA, &,,, .-I surfactant solutions with several concentrations, C, mmol dm-8.
4401 0
,
,
20
40
,
,
,
I
6 0 8 0 1 0 0
C / mmoldm-3
Figure 2. Plots of surfactant concentration, C, of DTAC and Experimental Section LiPFO vs maximum fluorescence wavelength of PCA, X, using different concentrations of PCA. PCA was obtained from Aldrich Chemical Co., Inc. Bis(hyMolar volumes of surfactants are from previous reportagpH or droxyethyl) (heptadecafluoro-2-hydroxyundecy1)methyla calculated from molar volumes of the molecular groups.'p8JO nium chloride, C$~,CH~CH(OH)CH~NCH~(C~H~OH)ZC~ (DEFUMAC)was prepared by an anion-exchangemethod in methanol from the corresponding iodine salt donated by Daikin Industries, Results and Discussion Ltd. Anionic fluorocarbon surfactants lithium perfluorooctaneFluorescence spectra of PCA in DTAC solution with sulfonate (LiFOS), lithium perfluorooctanoate (LiPFO), and several concentrations are shown in Figure 1. The lithium perfluorononanoate (LiPFN) were obtained by anionmaximumwavelength shifted to a shorter wavelength with exchange or neutralization from the corresponding products increasing concentration of DTAC above ita critical misupplied by Dainippon Ink and Chemicals, Inc., and Daikin. celle concentration (cmc),whereas it was constant at 472.5 Lithium dodecyl sulfate (LiDS), sodium dodecyl sulfate (SDS), CnHh+lN+(CH&CH2COO-, and N-alkyl-Nfl-dimethylbetaine, nm (=Aw) below the cmc. This tendency was the same for n = 12(DNB), 14(TNB),orl6(CNB),weresynthe&edaccording all the surfactants. In C12& and C12Ee systems,two peaks to the previously reported method.3~~ Other surfactants, alkylwere observed; the dominant peak was about 445 nm and trimethylammonium halide, C,,Hh+lN(CH&X (X= C1, Br; n = side peak was 391 nm. In Figure 2, the maximum 12 (DTAC, DTAB), 14 (TTAB), or 16 (CTAC, CTAB)), sodium fluorescence wavelength, A, is plotted against DTAC tetradecyl sulfate (STS),sodiumdodecanoate (SD),polyethylene concentration, C, for several PCA concentrations. X was glycol dodecyl ether (C12&, C12E8), AOT, and (tridecafluoroasymptotic to a certain wavelength (=Amic) in high suroctyl(sulfo(aminopropyl)))dimethylbetaine,C~~~C~H~SO~NHfactant concentration range, and hmicshould truly reflect C&N+(CH3)2CH2COO-(FOSAB), were obtained from Tokyo the polarity at palisade layer of the micelle. As shown in Kasei Kogyo Co. Ltd., Nikko Chemical Co., Ltd., and Atochem. Figure 2, the curves were independentof the concentrations All surfactants except Cl& and Cl& were recrystallized and the purities were checked by surface tension measurements. of PCA, but the curvatures of the asymptote were dePCA was added to surfactant solutions and shaken for a day pendent on kinds of the Surfactants; e.g., the curve of at 25 OC. The concentration of PCA applied in most of DTAC was asymptotic more rapidly than that of LiPFO. experiments was 10 pmol dm-3. About 20 solutions with various These results can be explained by assuming a partition concentrations were prepared for each surfactant. Fluorescence of PCA between micellar and bulk phases. The partition spectra of PCA excited at wavelength of 356 nm were measured with a Hitachi 650-10s at 25 OC. (5) Tamori, K.; Kihara, K.; Esumi,K.; Meguro, K. Colloid Polym. Sci., (1)Hayase, K.; Hayano, S. Bull. Chem. SOC. Jpn. 1977,50, 83. (2) Kalyanasundaram, K.; Thomas, J. K. J. Phys. Chem. 1977, 81,
2176. (3)Tamori, K.; Esumi,K.; Meguro, K. J. Colloid Interface Sci. 1991, 142, 236. (4)Beckett, A. H.; Woodward, R. J. J. Pharm. Pharmacol. 1963, 7, 422.
in press. (6)Kale, K. M.; h a , R. J. Colloid Interface Sci. 1977,61, 312. (7)Funaeaki, N.; Hada, S.; Neya, S. J.Phys. Chem. 1984,88,1243. (8) Vasa, S.; Torock, T.; Jakli, G.; Berecz, E.J. Phys. Chem. 1989,93,
6553. (9) Tauaka, M.; Kaneshina, S.; Nishimoto, W.; Takabatake, H. Bull.
Chem. SOC. Jpn. 1973,46, 364. (10) Berr, S . S.; Jones, R. R. M. J. Phys. Chem. 1989, 93, 2556.
0743-7463/92/2408-2344$03.00/00 1992 American Chemical Society
Langnuir, Vol. 8,No. 9, 1992 2346
Notes
coefficient of PCA, PPCA, and total concentration of PCA, CPCA,are given by
Table I. Data Obtained by PCA at 28 OC* cmc/mmol u/cm3 -AG~cAO/~J dm-3 Xdc/nm mol-' &A mol-' Hvdrocarbon Anionic LiDS 8.0 460.0 23.4 248 12300 SDS 455.8 7.2 248 9640 22.7 SD 25.1 456.6 195 12800 23.4 Hydrocarbon Cationic DTAC 21.6 449.0 285 6740 21.9 1.2 446.0 320 13400 23.6 CTAC 15.5 446.1 DTAB 287 4630 20.9 21.5 TTAB 3.7 444.1 318 5820 1.0 441.8 350 21.8 CTAB 6510 Hydrocarbon Nonionic 0.082 443.7 450 3220 20.0 ClZES 0.096 446.1 524 3650 20.3 CiaEs Hydrocarbon Betaine 2.4 445.0 280 14000 DNB 23.7 0.29 442.1 312 14600 TNB 23.8 24.4 CNB 0.10 439.1 343 18500 Fluorocarbon Anionic LiFOS 7.2 467.0 271 2180 19.1 LiPFO 29.6 467.5 200 1350 17.9 7.3 466.0 223 4570 LiPFN 20.9 Fluorocarbon Cationic DEFUMAC 2.9 460.5 379 3300 20.1 Fluorocarbon Betaine FOSAB 20.6 0.29 453.5 403 4020 Data of CTAB is obtained at 30 O C . Xdc is X at C = 100 mmol dm" except CNB (C = 10 mmol dm-3). u is estimated from experimental density data or from references. surfactants
PPCA CPCA
= CPcA"ic/CPcAw
= (cPCAmicvmic
(1)
+ c P C A w V ~ ) / ( v f i c + Vw)
(2)
where C ~ C and A CPCA, ~ ~ are the concentrations of PCA in the micellar and the aqueous phases, respectively, and V"ic and V, are the volumesof the micellar and the aqueous phases, respectively. From eqs 1 and 2 and V m i c
