4873
Langmuir 1995,11, 4873-4875
Notes NMR Spectroscopic Study on the Dissolution of Water in Sodium Bis(2-ethylhexyl) SulfosuccinatefI'oluene Solution Ayako Goto,*,+Hisashi Yoshioka,* Maeahiro Manabe,# and Rensuke Goto*
Department of Chemistry and Graduate School of Nutritional and Environmental Sciences, University of Shizuoka, 52-1 Yada, Shizuoka 422, Japan, and Department of Chemistry, Niihama National College of Technology, Uagumo 7-1, Niihama, Ehime 792, Japan Received September 6, 1994. In Final Form: June 30, 1995 0
2
4
6
8 1 0 1 2 1 4
R Introduction Figure 1. 1 7 0 line width of the Hz170 signal of AOT reversed The physical properties of reversed micellar solutions micelles as a function of the waterIAOT ratio R at various depend to a fair extent on the molar ratio of water to temperatures. In each sample AOT concentration in toluenesurfactant, R.' In the case of sodium bis(2-ethylhexyl) ds is 0.3 mol-kg-'. The width of the signal was measured at sulfosuccinate(AOT)/oil solution, discontinuity of several half-height at 27 (W), 35 (O),55 (A),and 65 "C (e). physical properties of solubilized water is observed at R = ca. Below R = ca. 10, water is bound to AOT polar Toluene-ds and water-"O (10.1%1'0) were purchased from Merck and CEA-ORIS, respectively. head groups and counter ions, but further addition leads NMR Measurements. NMR spectra were measured at 500 to the presence of free water in the core of a water pool, MHz ('HI and at 67.80 MHz P70)with a JEOL JMN-GSX 500 suggesting that the thickness of the hydration layer spectrometer at 27-65 & 0.2 "C. Air in the sample was replaced corresponds to nearly 10 water molecules. However, it is with N2 gas after degassing. Using the integralsof proton signals not clear whether the hydration layer is really homogeof water and AOT, the content of water was determined. AOT neous. The state of water in AOT reversed micelles, reversed micelle solutions containing waterJ70 were prepared especially below R = ca. 2, appears unusual and unclear. with enriched H2O (10.1% I7O). Final I7Oabundance in the water For example, Hauser et a1.2 reported that two water was ca. 3%. molecules are tightly bound to one AOT molecule by Results and Discussion measurement of DSC and deuterium NMR. It is not known whether the structure of the AOT Dynamic State of Water in AOTPToluene-dsSoluaggregate is maintained like a spherical reversed micelle tion at Small R. Since the 170and 2H relaxation rates a t small R. We measured the solution enthalpy of water of water reflect the motion of single water molecule^,^-^ in AOT/various organic solvents solutions, and a great the dynamics of water in AOT reversed micelle systems8 change in the state of solubilized water or AOT reversed have been recently studied by 170-and 2H-NMR specmicelles at small water content appeared to O C C U ~ . ~ ~ ~troscopy. The dynamics ofwater a t small R have not been Therefore, it is of interest to study the dissolution ofwater measured. In the present study, change in the dynamic in a n anhydrous AOT/organic solvent solution. In the state of water in AOT reversed micellesltoluene-ds with present study, we studied the effects of the successive R was examined by 170-NMR spectroscopy. Figure 1 addition ofwater on AOT aggregates and solubilizedwater shows line widths of 170-NMR spectra of water as a in toluene-& by 170-and 'H-NMR spectroscopy and function of R at various temperatures, where the spectra propose a new model of AOT aggregates and water were too broad to observe a signal below R = ca. 2 at 27 molecules at small water contents, different from the so"C (dotted line in Figure 1). The results showed that the called spherical reversed micelles containing a water pool motion of water below R = ca. 2 a t room temperature is formed by dissolving much water. greatly suppressed and line widths at small R are significantly influenced by temperature. The activation Experimental Section energy of the motion ofwater moleculeswould thus appear Materials. The purity of sodium bis(2-ethylhexyl) sulfosucto increase with decrease in R. TI of protons for water is cinate, Aerosol OT (AOT) purchased from Fischer Scientific was nearly constant below R = ca. 2, but increases with confirmed to be above 99% by 'H-NMR and HPLC before use. successive addition ofwater above R = 2 (data not shown) in good agreement with the results of 170-NMR. * To whom correspondence should be addressed. Chemical shifts of lH2O below R = ca. 2 were below 4 + Department of Chemistry, University of Shizuoka. ppm, but those above R = ca. 2 increased with R (datanot * Graduate School of Nutritional and Environmental Sciences, shown), suggesting the hydrogen-bonding structure of University of Shizuoka. water below R = ca. 2 to be fairly b r ~ k e n . ~ 0 Niihama National College of Technology. (1)Luisi, P. L.; Giomini, M.; Pileni, M. P.; Robinson, B. H. Biochim. Biophys. Acta 1988,947,209-246. ( 2 ) Hauser, H.; Hearing, G.; Pande, A.; Luisi, P. L. J. Phys. Chem. 1989,93,7869-7a76. (3)Goto,A,;Harada, S.;Fyjita, T.; Miwa,Y.; Yoshioka, H.; Kishimoto, H. Langmuir 1993,9,86-89. (4)Goto, A.; Yoshioka, H.; Kishimoto,H.; Fijita, T. Langmuir 1992, 8,441-445.
( 5 ) Llor, A.; Rigny, P. J.Am. Chem. SOC.1988,108,7533-7541.
(6)Yoshino, A.;Yoshida, T.; Takahashi, T.;Yeda, I. J.Colloidlnterface
Sci. 1989,133,390-394.
(7)Halle, B.;Carlstrom, G. J. Phys. Chem. 1981,85,2142-2147. (8)Carstrom, G.; Halle, B. Langmuir 1988,4 , 1346-1352. (9)Thompson, K.F.'; Gierasch, L. M. J.Am. Chem. SOC.1984,106, 3648-3652.
0743-7463/95/2411-4873$09.00/00 1995 American Chemical Society
4874 Langmuir, Vol. 11, No. 12, 1995
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b)
Notes ,COOR
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9
(1)
COOR
I,
a) anhydrous AOT
c) 2 < R
b)R
