Spectroscopic investigation of the mutual interactions between nonionic surfactant, hydrocarbon, and...

Spectroscopic Investigation of the Mutual Interactions between Nonionic Surfactant, Hydrocarbon, and Water

HUGO CHRISTENSON AND STIG E. FRIBERG*

Chemistry Department, University of Missouri, RoUa, Missouri 65401

Received July 9, 1979; accepted October 23, 1979

NMR, UV, and IR spectroscopy were used to determine the interactions in hydrocarbon solutions between polyethylene glycol alkyl ethers, water, and aromatic hydrocarbons. The results showed a concentration dependence for the site of benzene in benzene/surfactant solutions. At low concentrations the benzene molecules We~'e preferentially located adjacent to the surfactant oxyethylene chain with an even distribution along the chain. At high benzene concentrations a

" positive concentration gradient was found toward the hydrocarbon end of the oxyethylene chain. Addition of water increased this gradient except fo~ the octaethylene glycol dodecyl ether; for this compound the preferential water location appeared to be toward the central part of the oxyethylene chain.

INTRODUCTION

The phase behavior of water/hydrocarbon/surfactant systems has been exten- sively investigated during the last 10 years due to the problems of finding an efficient system for the tertiary oil recovery process. The interest has mainly focused on ionic surfactants of the petroleum sulfonate variety (1-5), while the nonionic surfactants have been more sparingly investigated in this context (6-8).

We have recently shown the strong temperature-dependent phase behavior of systems with nonionic surfactants to give rise to "infinitely" low interfacial tensions (9) and decided to investigate the molecular association/background to this phenomenon using spectroscopy. The aqueous micellar solubility region of a water/polyethylene glycol alkyl ether/hydrocarbon system con- tinuously changes to an isolated" surfactant phase" and finally to an inverse micellar solution with a limited (~25°C) temperature rise (10-15). This behavior has been referred to the variation with temperature

* To whom correspondence should be directed.

in the water/polyethylene glycol chain interaction shifting the relative surface pressures in the hydrophilic and hydrophobic parts of the duplex surfactant film (16), giving normal micelles at low temperatures and inverse micelles at higher temperatures.

Accepting this model leads to a con- sequence of the surface pressure ratio being influenced by the nature of the hydrocarbon; the temperature for the shift from normal to inverse micelles [the HLB temperature (10)] is reduced as much as 50°C when changing from an aliphatic to an aromatic hydrocarbon. Any molecular model to account for this behavior must include specific interaction of water and hydrocarbon with different parts of the surfactant molecule.

The most direct information about such interactions would be from spectroscopy data; but a literature search revealed only limited information (17-20), mainly on the system water/polyethylene glycol alkyl ethers. Corkill and collaborators (17) found an upfield shift in the water proton signal and a decrease in its longitudinal relaxation time for increased concentrations of polyethylene glycol monoalkyl ethers in aqueous

0021-9797/80/050276-10502.00/0 Copyright © 1980 by Academic Press, Inc. All rights of reproduction in any form reserved.

276

Journal of Colloid and Interface Science, VoL 75, No. 1, May 1980

SPECTRA: NONIONICS/HYDROCARBON/WATER 277

solutions. The results showed only insignificant discontinuities when a phase transition to a liquid crystalline phase occurred. Nemethy and co-workers (19) studied the changes at micellization in aqueous solutions finding an environmental shift of the hydrocarbon chains to a less polar one. The experiments with hydrocarbon solvents gave results indicating variations in the interaction of various seg- ments with neighboring benzene rings. Lincoln et al. (20) made investigations on the bonding in water/carboxylic acid/nonionic surfactants.

These investigations have provided valu- able information on the behavior and interaction of nonionics with hydrocarbon and water but several essential questions remain to be answered. Among these the most important is the mutual dependence of the water and hydrocarbon interaction with the different parts of the nonionic surfactant. This mutual influence is the key factor for the drastic changes in the micellar behavior with temperature but has so far not been investigated.

We judged these problems to be sufficiently important to justify an investigation of the hydrocarbon/emulsifier/water interaction on a molecular level. This intro- ductory report shows these conditions for a surfactant at sufficiently low concentration in hydrocarbon to be unassociated. Higher concentrations of surfactant lead to self- association and the evaluation of bonding features of water becomes obscured. Knowledge about the conditions at a single nonassociated molecule is a necessity for a later clarification of the conditions at higher concentrations.

E X P E R I M E N T A L

Materials

The polyethylene glycol dodecyl ethers were all from Nikkol Company, Japan, and of a purity of at least 98% as determined by gas chromatography. The names of the poly-

ethylene glycol dodecyl ethers will be given only by the first part (e.g., pentaethylene glycol dodecyl ether = penta). The water was doubly distilled. The remaining chemicals, used without further purification, are listed in Table I with the origin and purity as listed by the manufacturer.

Sample Preparation

Samples were prepared by weighing the components into glass vials. For the com- binations for which information on the maximum water solubility was not available samples with maximum water solubility were prepared by direct pipet removal of the phases from two-phase systems equili- brated at 30°C for at least 1 hr.

NMR Spectra

The NMR spectra were run on a Varian EM-360 spectrometer with a probe temperature of 30 _+ 2°C with TMS as an internal reference. The samples run without TMS to check for effects on the relative signal positions showed only differences within the margin of spectrometer accuracy.

A representative selection of the samples was run on a JEOL 100-MHz Fourier- transform NMR spectrometer at 30 _+ 0.5°C to obtain better resolution and compare the results. The results agreed completely and no new features were added to the spectra.

Systems Investigated

The hydrocarbon/emul~ifier solution with solubilized water in the system penta- oxyethylene dodecyl ether/water/benzene (Fig. 1) was investigated using the samples marked in Fig. 1. The results of these determinations enabled a reduction of the number of samples in other systems. The following samples were investigated (per- centages are by weight):

1.5% solutions in benzene and solutions with an emulsifier to benzene ratio of 1:50;

2. 5 and 10% solutions in benzene with small amounts of water;

Journal of Colloid and Interface Science, Vol. 75, No. 1, May 1980

278 CHRISTENSON AND FRIBERG

TABLE I

Chemicals

Benzene Toluene para-Xylene Carbon tetrachloride n-Hexane Cyclohexane Ethylene glycol monobutly ether Cycloheptatriene 1,3,5,7-cyclooctatetraene Tetraethylene glycol Phenylacetylene Cyclopentene Decane Mesitylene Cyclohexane Cumene Hexadecane Phenyldodecane 1-Bromonaphthalene Diethylene glycol Diglyme Polyethylene glycol, MW 400 Polyethylene glycol monomethyl ether, MW 350 Tetraethylene glycol dimethyl ether

Fischer cert. Fischer cert. Fischer cert. Fischer cert. 99% Fischer cert. Fischer cert. Fischer cert. Aldrich 97% Aldrich 98% Aldrich Aldrich 98% Aldrich 99% Eastman Practical grade Eastman Practical grade Eastman Practical grade Eastman Practical grade Matheson, Coleman and Bell 99% ICN Pharmaceuticals Bausch & Lomb BDH Chemicals 99%

Polysciences Polysciences Polysciences

3. pure polyoxyethylene dodecyl ethers; 4. ethers with solubilized water, the exact

amounts varying.

IR Spectra

Infrared measurements were performed on a Perkin-Elmer 599 spectrometer at ambient temperature using variable-path- length cells with sodium chloride windows for both sample and reference.

UV Spectra

The UV spectra were obtained using a Cary recording spectrophotometer, Model 14, at a temperature of 30°C. The cell path length was 1 mm, except for benzene in water for which a 10-ram cell was used, and the pure solvents were used as blanks. Absorbance values were obtained as an average of measurements on three suc- cessive scans.


Synthesis

Pentaethylene glycol dodecyl methyl diether, C12H25[OCH2CH2]~OCHs, was syn- thesized by refluxing a solution of penta in benzene with metallic potassium and methyl iodide. Potassium iodide and excess po-

Water

Benzene

Penta

FIG. 1. The phases at 30°C and the compositions of NMR samples in the system water/pentaethylene glycol dodecyl ether/benzene.


.=01

41o 315 31o

JL 2.5 2.0 1.5 1.0 05 O.O

chemical shift (ppm)

not affected (16). For mona, di, and tri the signals of the water and the hydroxyl proton were coalesced, while tetra, penta, hexa, and octa showed separate signals and spin- spin splitting for the hydroxyl proton.

The downfield shift is expected with the presence of water; a change of the group environment toward enhanced polarity will give a downfield shift (21).

4.0 3.5 50 2.5 2.0 1.5 1.0 0.5 0.0 chemical shift (ppm)

FIG. 2. The PMR spectra of pentaethylene glycol dodecyl ether (A) and monoethylene glycol dodecyl ether (B) in their native state.

tassium were removed by filtration and benzene and methyl iodide by evaporation. Infrared spectra showed a maximum of 10% unreacted hydroxyl groups.

RESULTS

The peaks of the NMR spectra of the compounds in the pure state (Fig. 2) have been previously assigned (17). Here we use the representation.

a b c d EO l EO2,3...n. l e f g

CH 3 - (CH2) 9 CH 2 CH 2 0 CH 2 CH 2 0 [CH 2 CH 20]n_ 2 CH 2 CH 2 OH (1)

where n = number of oxyethylene units.

Surf actant /Water

Solubilized water shifted the oxyethylene peak (EO1-EO,) downfield whereas the alkyl chain proton resonance peaks were

S urf actant /Hydrocarbon

Addition of benzene gave no changes in the chemical shift of the alkyl chain protons relative to TMS. This means that the change of benzene concentration within the nonpolar part of the surfactant molecule was exactly the same as the one experienced by the TMS probe. Orientational effects are insignificant in a medium of this kind (21).

On the other hand, the addition of benzene caused dramatic changes in the appearance of the ethylene oxide resonances as exemplified by the spectra for the penta solutions of which 25 samples of concentrations varying from 1 to 99% benzene by weight were run. At benzene concentrations between 40 and 50% the main ab- sorbancy was separated into two peaks and at about 70% benzene a third peak could be observed (Fig. 3). Further dilution caused no additional changes in the number of resonance frequencies but they moved

2 3 0 -

~ 2 . 2 0 E

,,o

<~2.1o

2 . 0 0

2 '0 ' 4"0 " 6 '0 ' 8 '0 ' Weight i~ benzene

FIG. 3. With increased benzene content the single resonance frequency of the oxyethylene groups in pentaethylene glycol dodecyl ether was split into two (45-50% C6H6) and three (~70% C6H6) frequencies.

Journal o f Colloid and Interface Science, VoL 75, No. 1, May 1980


farther apart. In addition there was an over- all upfield shift, greater for the high-field frequencies than for the low-fiield ones. The hydroxyl group resonance was shifted upfield and was eventually obscured by background noise as the concentration decreased.

This behavior should be related to the generally expected shift of the resonance frequencies due to the presence of a benzene group (21). The change of chemical shifts depend on the relative orientation of the benzene molecule and the group in question. Groups localized close to the benzene molecule in the extension of the benzene molecular plane show a small downfield shift, while an out-of-plane location will give rise to an upfield shift. Since orientational effects probably are of minor importance a reasonable interpretation is increased concentration of benzene adjacent to the polar part of the surfactant molecule in comparison with the nonpolar part.

As a group the different polyethylene glycol dodecyl ethers displayed a systematic variation in the numbers of resonance frequencies for the oxyethylene groups in dilute benzene solutions (Fig. 4). Dissolving mono, the native compound multiplet con- sisting of the d, e, and f protons was separated into two triplets of integral ratio 2:1; the larger one moved upfield, the smaller one downfield (Fig. 4A). For the higher homologs the protons from the remaining oxyethylene groups gave a number of resonance frequencies (rf) that varied with the number of groups as: Fig. 4B, di (1 rf); Fig. 4C, tri (2 if:s); Fig. 4D, tetra (3 if:s); Fig. 4E, penta (3 if:s); Fig. 4F, hexa (4 if:s); and Fig. 4G, octa (4 if:s). Further dilution in benzene gave no changes in the number of absorption maxima.

Since these results indicated a change in the site of interaction of the hydrocarbon with concentration it was deemed necessary to obtain further information about the influence of the nature of the hydrocarbon on the interaction with the surfactant and a series of penta spectra in various hydro-

Journal of Colloid and Interface Scienc(, Vol. 75, No. 1, May 1980

4"0 ~ (ppm) 3.0 4.0 ~ (ppm) 3.0

G

_lJk_ 4.0 3.0

(ppm)

FIG. 4. The NMR spectra of the oxyethylene ethylene groups of mono- (A), di- (B), tri- (C), tetra- (D), penta- (E), hexa- (F), and octaethylene glycol dodecyl ether (G). The last spectrum was from a sample with a benzene/suffactant molecular ratio of 100; for the other samples this ratio was 50.

carbons was determined. Separation and upfield shifts similar to those for penta in benzene were obtained for solutions in 1- bromonaphthalene, styrene, toluene, para-

xylene, mesitylene, cumene, and phenylacetylene with the latter giving a separation of different integral ratios. Phenyldodecane and carbon tetrachloride gave small effects at high dilution while n-hexane, cyclohexane, cyclopentene, cyclohexene, cycloheptatriene, and cyclooctatetraene displayed none of the above-mentioned effects except for a slight separation of the "shoulder" on the upfield side.

These results indicated a relation between aromaticity and the change in the ethylene oxide resonance pattern. An empirical measure of the influence was obtained in the following manner. Using a concentration of 1 mole penta per 30 moles of aromatic rings, the separation of the two outermost peaks of the EO signal group was measured and the result tabulated for comparison (Table II). The trend of increased separation of the two outermost resonance frequencies with increased aromaticity is immediately obvious.

S P E C T R A : N O N I O N I C S / H Y D R O C A R B O N / W A T E R 281

T A B L E II

S e p a r a t i o n

A~

1-Bromonaphthalene 0.113 Styrene 0.092 Benzene 0.083 Toluene 0.070 para-Xylene 0.057 Cumene 0.052 Mesitylene 0.048 Phenyldodecane 0.015

In order to assist in the interpretation and assignments of the above-mentioned spectra, it was necessary to resort to compari- sons with spectra of other ethylene oxide derivatives.

Other Ethylene Glycol Compounds/Hydrocarbon

Spectra of di-, tetra-, and polyethylene glycol as well as polyethylene glycol monomethyl ether in benzene gave a separation effect for the EO signal similar to that of the polyoxyethylene dodecyl ethers (Figs. 5 C-D).

4..0 (~ (ppm) 3.0

5.0 4.0 3.0 (ppm)

FIG. 5. The NMR spectra of native pentaethylene glycol dodecyl methyl ether (A), the same in a 5% solution in benzene (B); native diethylene glycol (C), the same in a 2.5% solution in benzene (D); native diethylene glycol dimethyl ether (E), the same in a 5% solution in benzene (F).

FlG. 6. The NMR spectra of 5% solutions in benzene of penta- (A), hexa- (C), and octaethylene glycol dodecyl ether (E); polyethylene glycol (G); polyethylene glycol monomethyl ether (I); and spectra of the same with small (-0.2%) amounts of water (B, D, F, H, J).

No further peaks were resolved upon dilution in benzene; only an upfield shift was evident for the dimethyl ethers of di- and tetraethylene glycols and for the penta- oxyethylene dodecyl methyl ether (Figs. 5A, B, E, F).

Oxyethylene Compounds/ Hydrocarbon~Water

The addition of water to the hydrocarbon emulsifier solutions caused specific effects. The long-chain (n - 5) surfactants and the polyethylene glycol compounds responded with a split of one of the resonances. This behavior is observed by comparison of spectra A and B, C and D in Fig. 6 showing the influence of water on the surfactant molecules in benzene solution. Comparing spectra I, J, G, and H of Fig. 6 demonstrates similar behavior for polyethylene glycol and polyethylene glycol monomethyl ether.

Assignment of Resonance Frequencies

A comparison of the NMR results enables an assignment of the different resonance



frequencies to specific groups in the polyethylene glycol chain for dilute solutions of the surfactant in benzene. The oxyethylene group adjacent to the OH group was split and could not be observed among the dominant resonances of the remaining ones. Of these the two with the most upfield resonance positions showed constant intensity for different homologs. They were assigned oxyethylene group numbers 1 and 2 counted from the hydrocarbon chain; an assignment supported by the invariance of their relative position and intensity with addition of water (Fig. 6). The most downfield f requency for tetra (Fig. 4D) was found with doubled intensity for penta (Fig. 4E) remaining constant for hexa and octa. This absorption was split by addition of water in the case of penta and hexa (Figs. 6, A - D ) and was assigned to the group(s) marked EOT (Fig. 7). The variation of in-

EOTP E02 E 0 1

downfield

I \

R!CI-120-~EO-H , ; ' , , i ,

R~CH20~EO-~-EO-H

mono

di i i i i i tri RI Ct'120"1EO ]

i i i tetra R!CH,zO!EO

i i i i penta R~CH2OI(EO

i i ~xa .ic~ot~o, i i

octa RICHzO~EO,

EO 1

" , , e , f ,g EO~EO-H

'-"t El EO~ EO-H

E, EO~-EO~EO-H

E, EOkEO4Ed•O-H

E, - ~o -E? ;~o -~o . P ' EO T '

EO 2

FIG. 7. Assignment of resonance frequencies for the dilute solutions of the polyoxyethylene dodecyl ethers in benzene. EOr = oxyethylene group(s) next to the terminal one. p = oxyethylene group(s) bridging EO2 and EOr. - - - , separation of peaks caused by benzene. . . . . . , additional separation induced by water.

,60"

'6 ~.4o. ®

5 ~.20.

i t

d' I /" i

f I / j

/ ' 7 J / ' i / , I

. . i I ~.~.~

r':'..-:'T . . . . . 5 0

solvent,weight %

FIG. 8. Ratios of the free to total OH stretching for solutions of penta in benzene (e) and cyclohexane (11). • denotes the ratio of the cyclohexane to benzene ratios.

tensity, the position (Figs. 4F, G), and its indifference to the presence of water in the case of hexa (Figs. 6C, D) made the assignment of the remaining groups as EOp (Fig. 7) probable.

IR Spectra

Infrared spectra of penta in benzene and cyclohexane demonstrated the extent of hydrogen bonding to be greater in cyclohexane than in benzene. The absorbance ratio of the free to the t o t a l - O H stretching plotted against concentration in weight percentage is found in Fig. 8.

UV Spectra

Following the method descr ibed by Cardinal and Mukerjee (22, 23) polarity- sensitive spectral characteristics of benzene, first in a number of solvents of different polarity and then in pentaethylene glycol dodecyl ether (and penta + 10% water), were calculated. The benzene concentrat ion was 0.5 + 0.2% in all cases, except for the aqueous solution ( -0 .05%). The ratio of the absorbances at the first major peak ( -260.4 nm) on the long-wavelength side and at the valley ( -259 .0 nm) preceding it on the short-wavelength side was used as the polarity-sensitive spectral characteristic (Table III). The results showed the benzene environment for low concentrat ions of benzene to possess a polarity between



TABLE III

Polarity-Sensitive Ratios

Solvent Rpv

Decane 5.26 Hexadecane 4.69 Ethylene glycol monobutyl ether 3.44 Penta 3.24 Penta + 10% W 2.86 Diethylene glycol 2.62 Tetraethylene glycol 2.57 Water 1.91

diethylene glycol and ethylene glycol monobutyl ether. Addition of water enhanced the polarity bringing it closer to the one of diethylene glycol.

DISCUSSION

The results illustrated the importance of weak intermolecular forces from aromatic hydrocarbons for the location of them in the vicinity of a nonionic surfactant with a polyethylene glycol alkyl ether group and also gave information on the mutual position of hydrocarbon and water adjacent to the polar part of the chain. The results in general appeared supportive of the possibilities to relate the variation of the strong temperature dependence of micellar structure with the hydrocarbon nature to occupation of different sites by different hydrocarbons.

The results from UV, IR, and NMR agreed in showing the aromatic hydrocarbons to be preferentially located in the immediate environment of the polar chain of the surfactant. The UV results showed the average environment of the aromatic group to be more polar than ethylene glycol monobutyl ether but less so than diethylene glycol. Considering the fact that the penta contains proportionally less polar groups than the butyl ether, a considerable part of the benzene initially added to the penta is located close to the polar parts of the surfactant. An assumption of linearity of the UV absorption ratio at 260.4 and 259.0 nm

with the benzene partition gave a ratio of benzene amount located in a polar (tetraethylene glycol) to nonpolar (decane) environment of 3.5 at small concentrations of benzene. An approximate volume ratio of polar to nonpolar parts of the penta molecule may be calculated by dividing the group weights of the nonpolar and polar parts by the density of hydrocarbon and tetraethylene glycol. The result gives a polar/nonpolar volume ratio of 0.9 changing the concentration ratio of benzene in a polar/ nonpolar environment to almost 4.

This estimation indicates initially added benzene to be preferentially located in a polar environment in the water-free surfactant liquid. The infrared spectra results supported this conclusion for high solvent concentrations. The surfactant molecules gave higher nonbonded/hydrogen bonded ratio in benzene than in cyclohexane (Fig. 8) demonstrating a stronger interaction of the polar part of the surfactant molecule with benzene than with cyclohexane.

The NMR results were also in agreement with this concept; the accelerated upfield shift with addition of benzene is obvious from Fig. 3. With orientational effects probably insignificant the conclusion of a high concentration of aromatic hydrocarbon along the polar part of the structure appears to have a solid foundation in the experimental results from the three methods used.

The harmony of the interpretation of the results from the three experimental methods indicating the aromatic hydrocarbons to be located mainly within the polar part of the nonionic surfactant forms a basis for a qualitative explanation of the dependence of the HLB temperature on the nature of the hydrocarbon present using the micellar model (16) with a duplex film of the surfactant polar and nonpolar parts forming. The combination with an aromatic hydrocarbon gives rise to an inversion of aqueous micelles to inverse micelles at a temperature lower than that for aliphatic hydrocarbons. The reason for this difference may be found


284 C H R I S T E N S O N A N D F R I B E R G

in the aromatic molecules being located closer to the polar part of the molecules exerting a stronger "wedging effect" than aliphatic hydrocarbons which are localized within the surfactant hydrocarbon space. The alkyl chains of the surfactant are in fact in a liquid state and little wedging effect may be expected.

The NMR results also gave more detailed information on the interaction between benzene and the polar part of the surfactant. This interaction is illustrated by the results from increased addition of benzene (Fig. 3), showing a more enhanced upfield shift for groups close to the hydrocarbon chain as (EOi and EO2, Fig. 8). These multiple resonance frequencies are not a result of coupling (as shown by a greater separation at 100 MHz); they are due to preferential sites of benzene along the polyoxyethylene chain.

The assignment of the resonance frequencies (Fig. 7) applied to the results in Fig. 3 gives the following picture of the gradual concentration change with the addition of benzene. With small additions of benzene to the water-free surfactant, the resolution of the instrument (100 MHz) permitted only one signal to be observed. This signal moved upfield with increased benzene addition as expected (24-26). The separate resonance frequency appearing at compositions between 40 and 50% benzene is assigned to enhanced concentration of benzene close to the oxyethylene groups EO1 and EO2 (Fig. 7). Seventy percent and higher benzene content gave further separation. The second oxyethylene group from the hydrocarbon chain now was more influenced by the presence of benzene.

This interpretation is supported by the infrared spectra showing considerable dis- sociation at benzene concentrations in excess of 50%. It appears reasonable to assume a precursory separation of the oxyethylene groups close to the hydrocarbon chain prior to the separation of the hydrogen bond.


For the octa compound three oxyethylene groups showed an identical signal (Fig. 4G); they are marked P in Fig. 8. This behavior may be understood from the structure of the oxyethylene chain in dilute hydrocarbon solution. According to Tadokaro (27) the oxyethylene groups of polyethylene glycol form a helix with 7.2 groups per revolution. Such a structure implies a complete turn for the octa compound and a spectroscopical equality of the groups diametrically opposite the hydrocarbon chain/OH group location appears probable.

The concentration gradient along the polar chain critically depended on the presence of the OH group in the surfactant as exemplified by the behavior of the surfactants and the monoether of di- and tetraethylene glycol. On the other hand, neither the methylated surfactants nor the dimethyl ethers of the di- and tetraethylene glycol gave the separation of the resonance frequencies from the oxyethylene groups. Instead the single frequency was shifted upfield with the addition of benzene, indicating no preferential site for the hydrocarbon along the polar surfactant chain. This behavior should be viewed in the light of earlier investigations (24-27) on the interaction between benzene and polar compounds having been interpreted as the benzene molecules being transiently oriented by local solute dipoles to solvate the positive end of the dipole. The present results are a further illustration of this effect.

The assignments (Fig. 7) also gave reasonable interpretation of the effect of added water to surfactant/benzene solutions. Figure 6 shows the resonance frequency of the two oxyethylene groups adjacent to the terminal one (EOT, Fig. 8) to be split by the addition of water with one of the frequencies being moved upfield, indicating an enhanced concentration of benzene. The interpretation into a molecular model is obvious. The water was concentrated toward the OH group of the oxyethylene chain, the hydrocarbon being displaced further toward the


alkyl chain, resulting in an enhanced benzene concentration at the oxyethylene groups close to the hydrocarbon chain.

With an enhanced number of oxyethylene groups the water molecules exerted an influence on a proportionally higher number of the groups.

The octa compound was an exception. For this compound a comparison of the spectra in Figs. 6E and F showed no change of intensity of the absorption from the two oxyethylene groups adjacent to the terminal one. Instead the split occurred for the group Nos. 4 -6 counted from the terminal one as No. 1. This result may be interpreted as a preferential accumulation of water molecules added to the center of the oxyethylene chain. Such a behavior may be compre- hended considering the helical structure of the polar chain. With the octa compound the complete turn (27) would place the OH group in the vicinity of the hydrocarbon chain; an initial site of the water molecules diametrically opposite on the helix turn appears reasonable. The influence of the different changes has been summarized in Fig. 7B.

This first investigation was concerned with the relative coverage in dilute solutions; the coincidence between the composi- tion for the split frequency (Fig. 3) and the enhanced solubilization of water (Fig. 1) has not been treated. Such investigations will be reported.

ACKNOWLEDGMENTS

This research was funded by the National Science Foundation, Grant DMR76-23569. We thank Gerry Sullivan and the Chemistry Department, Washington University, for help in obtaining spectra from the JEOL spectrometer.

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Journal of Colloid and lnterJace Science, Vol. 75, No. I, May 1980

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