J. Phys. Chem. 1083, 87, 695-696
kanes. Thus, by shifting, e.g., the spacing vs. temperature curves along the temperature axis in Figure 6, one obtains a master curve for parameters a. and bo. For the ao/bo ratio a similar master curve can be constructed. Its slope increases as the hexagonal lattice value of 31/2is approached. Such a trend with increasing temperature is viewed as a very conspicuous pretransition behavior in the rotator phase, ending with the weak FCO rhombohedral transition. A proper physical interpretation of the whole phenomenon still has to be given. At present we envisage that it should be considered in terms of an order-disorder transition where the hypothetical "ordered" state already involves several (n) equivalent molecular orientations and is most closely approached by the FCO phase in shortest paraffins. The disordered state, i.e., the hexagonal (rhombohedral) form, would be characterized by a still larger n and also, as recent evidence suggests: by a considerable number of kink defects. Judging by the quasielastic neutron scattering results," n 1 8 in the FCO phase of CI9H,. There is also neutron scattering evidencez4of
-
605
substantial longitudinal chain motion in the rotator phase which appears to be the prime source of the high selfdiffusion rate observed.25
Acknowledgment. Preliminary experiments in this study were performed at the Physics Department, University of Bristol, where some of the paraffins were also obtained by courtesy of Professor A. Keller. I also thank Mrs.N. Vene and Dr. A. Prodan of the Jozef Stefan Institute, Ljubljana, for their help and advice with the use of the Guinier-LennB camera, and Dr. V. Marinkovie for his kind permission to use the X-ray equipment. Registry No. Undecane, 1120-21-4; tridecane, 629-50-5; pentadecane, 629-62-9; heptadecane, 629-78-7; nonadecane, 629-92-5; heneicosane, 629-947; tricosane, 638-67-5; pentacosane, 629-99-2; heptacosane, 593-49-7; hentriacontane,630-04-6. ~~~~~
~
(24) D. Bloor, D. H. Bonsor, D. N. Batchelder, and C. G. Windsor, Mol. Phys., 34, 939 (1977). (25) G. Ungar and A. Keller, Colloid Polym. Sci., 267,90 (1979).
Hydration Numbers by Near-Infrared Spectrophotometry. 2. Sugars J. Leland Hollenberg' and David 0. Hall Department of Chemlsby, Unlverslty of Redlands, Redlands, California 92373 (Recehred:August 3, 1982; In Flnal Form: October 79. 1982)
A near-infrared differential spectrophotometricmethod of determining hydration numbers of solutes in aqueous solution was applied to eight different sugars at 25 O C . For some of these the influence of concentration was determined and the effect of higher temperature on the measured hydration numbers was investigated.
In a previous paper' the method of Bonner and Woolsey2 was applied to the determination of hydration numbers of 16 different amino acids. This method makes use of near-infrared differential absorbance of an aqueous solution of the solute compared to pure water at a fixed wavelength of 958 nm. Because few studies of hydration numbers of small molecules of biological interest have been reported, the investigation of a number of common sugars was undertaken. Commercial samples of the sugars were used without further purification. Each was dried in a vacuum oven at about 60 "C for at least 24 h and stored in a desiccator. In the case of raffinose, which was purchased as a hydrate, prolonged vacuum drying was required to completely remove all of the water, as indicated by constant weight. The differential absorbances were measured in 10-cm silica cells in a Cary 14 spectrophotometer equipped with thermostatted cell jackets. A zero level of absorbance was established by fiiing both sample and reference cells with degassed, deionized water. After filling a cell with either solution or water, we found that it was necessary to wait at least 30 min to achieve thermal equilibrium, as evidenced by absorbance values which remained constant for (1)J. L. Hollenberg and J. B. Ifft, J.Phys. Chem., 86, 1938 (1982). (2) 0.D.Bonner and G. B. Woolsey, J.Phys. Chem., 72,899(1968). 0022-3654/83/2087-0695$01.50/0
TABLE I: Hydration Numbers of Sugars sugar concn, % temp, "C glucose glucose fructose fructose fructose mannitol ribose sucrose sucrose sucrose sucrose lactose maltose raffinose
2
4 2 2 4 2 2 2 2 4 4 2 2 2
25 25 25
40 25 25 25 25 40 25 40 25 25 25
n 10.3 10.0 12.8 12.0 10.9 10.8 5.7 25.8 23.8 22.5 21.6 25.1 24.0 19.3
a 5-min interval. The 04.1 absorbance slidewire was used in all measurements. With the monochromator set at a constant wavelength of 958 nm, absorbance values were recorded for at least 1min to attain maximum precision. Our studies showed that glucose had almost no dependence of the hydration number n on concentration. Investigations of fructose and sucrose showed a little dependence on concentration. After obtaining these results, we assumed that the other sugars were unlikely to show marked concentration dependence of n. Thus we did not extrapolate values of absorbance over molality, A l m , to 0 1983 Amerlcan Chemical Society
J. Phys. Chem. 1983, 87,696-707
696
zero concentration as was done with most of the amino acids studied in the previous paper. All of the concentrations used were either 2 or 4 % by weight. Results of our work are summarized in Table I. The value 10.3 for glucose agrees very well with the value 10.0 reported by Bonner and Woolsey. The value 25.8 for sucrose is somewhat higher than the value 21.0 found by these same authors, although they gave no indication of concentration or temperature. Another comparison is possible by using the results of Goto and I ~ e m u r a . With ~ an ultrasonic interferometric method they obtained 2.4 for mannitol and 3.4 for sucrose. One additional comparison is possible using the work of Novodranov and Mal'tsman4 as reviewed by Hinton and ami^.^ From the speed of ultrasonic waves in aqueous solutions of sucrose, galactose, arabinose, maltose, and lactose, the Russian authors calculated that 2 molecules of water were linked to each OH group. Our results agree well with this finding, even though their method was entirely different from ours. There is a possibility that the solute molecules themselves may absorb some light at 958 nm, resulting in serious errors in the calculated n values. To test this, 10% solutions of glucose in D20 and of sucrose in D 2 0 were prepared. Spectra of these solutions in a 1-cm cell vs. air showed no significant differences from a spectrum of D20 vs. air. Thus we have good evidence that absorption by these two solute molecules is negligible, and it seems reasonable to assume that the other sugars behave similarly. (3) S. Goto and T. Isemura, Bull. Chem. SOC.Jpn., 37, 1697 (1964). (4) Yu. D. Novodranov and S. N. Mal'tsman, Uch. Zap. Leningr. Gos. Univ. im. A. A. Zhdanoua, Ser. Khim. Nauk, lo., 163 (1951). (5) J. F. Hinton and E. S. Amis, Chem. Reu., 71, 627 (1971).
Raffinose was studied after most of the other sugars, and the value we expected for n for this trisaccharide was about 35. The experimental result of 19.3 was suprisingly low, but there is a possible partial explanation. Because raffinose is formed from three monosaccharide units, the two ends can be folded over the middle unit. By assembling a CPK model of raffinose and attaching H 2 0 models to readily available oxygen sites, it was apparent that three intramolecular H bonds can form, thus, stabilizing the folded configuration. In addition, there are at least five H-bond sites for water molecule attachment which are excluded by steric hindrance in the folded configuration. There are also two sites where an H 2 0 could form bridge H bonds between different monosaccharide units. Thus there could be at least 10 fewer water molecules in a primary layer held by H bonds for the folded configuration of raffinose. Models of monosaccharides show that up to 12 water molecules can readily be held by H bonds, two on each 0 atom. The rather low value of n = 5.7 for ribose can be accounted for with models. Ten H 2 0 molecules can be held with single H-bonds, but the close proximity of the 0 atoms allows four H20 molecules to form double H bonds, thus reducing the primary layer to 6. We are hesitant about attaching too much significance to these model explanations, for there is no evidence that H20 molecules in a primary layer are included in n and that those in a secondary layer are excluded. Moreover, such inferences from models do not seem to lend themselves to account for the measured n values of amino acids in aqueous solutions. Registry No. Glucose, 50-99-7;fructose, 57-48-7; mannitol, 69-65-8;ribose, 50-69-1;sucrose, 57-50-1;lactose, 63-42-3;maltose, 69-79-4; raffinose, 512-69-6.
Transport Properties of Diluted Inverted Micelles and Microemulsions J. R. Lalanne;
B. Poullgny, and E. SeIn+
Universi?y of Bordeaux 1 and CNRS Research Center Paul Pascal, Universi?. Domain, 33405 Talence, France (Receivd: June 10, 1982; In Final Form: June 18, 1982)
We report experimental results concerning three transport properties: viscosity, mass diffusion,and heat transfer in the ternary system sodium bis(2-ethylhexyl)sulfosuccinate (AOT)/water/CCI,. Thermal conductivity has been investigated by a thermal lens technique (TLT)using a single laser pulse in the microsecond range. The results are discussed and compared by using a model based upon the kinetic theory of fluids. Finally, we show how such investigations can lead to an original determination of the intermicellar potential in microemulsions.
I. Introduction Forty years ago, Schulman' began the study of the physical chemistry of quaternary systems consisting of water, oil, alcohol, and amphiphilic surfactant (soap). In fact, such mixtures present a strange behavior. During preparation, the mixtures suddenly undergo a transition from a milky appearance to quasi-transparence. Schulman supposed the presence of microdroplets of oil, surrounded by a shell of soap, imbedded in water. It is only 20 years later that the first fundamental work was completed by systematic investigations, stemming from the important Present address: Centre National d'Etudes Spatiales, 31055 Toulouse, France.
applications of microemulsions in many fields of the chemical industry. Recently, projects on enhanced oil recovery2 led to a spectacular increase of fundamental research in this domain. Consequently, a lot of information has been obtained on this subject. In particular, phase diagrams of these quaternary systems have been intensively ~ t u d i e dand , ~ a review paper has been p ~ b l i s h e d . ~ However, Schulman's model does not give any information about the volume and the shape of micelles, and the dif(1) J. H.Schulman and T. P. Hoar,Nature (London),162,102 (1943). (2) M. Baviere, Rev.Inst. Fr. Pet., 29, 41 (1974). (3) P. A. Winsor, Trans. Faraday Soc., 44, 376 (1948). (4) K. Shinoda and S. Friberg, Adv. Colloid Interface Sci., 4, 281 (1975).
0022-3654/83~2087-0696$01.50/0 0 1983 American Chemical Society
