312
Langmuir 1990, 6, 312-317
Art i d e s Detergency of a Nonionic Surfactant toward Tristearin Studied by FT-IR David R.Scheuing Clorox Technical Center, Pleasanton, California 94566 Received December 5, 1988. I n Final Form: May 15, 1989 The interfacial interactions of an aqueous ethoxylated alcohol solution and a “model soil”, tristearin, have been studied by Fourier transform infrared spectroscopy (FT-IR). The time-resolved spectroscopic changes can be used to elucidate the mechanism of detergency in the case of a solid oily soil. The spectroscopic changes suggest that the removal of solid triglycerides from a surface is more complex than in the case of a solid hydrocarbon soil because of the polymorphism in crystal structure exhibited by triglycerides. Interpretation of the spectra suggests that the CY polymorph is readily removed by the surfactant solution. Exposure of the CY phase to surfactant, however, accelerates the CY to 0 crystal transition. The 0 polymorph is more resistant to removal and comprises the fraction of residual soil left after the detergency process.
Introduction The detergency of solid oily soils, because of its complexity, is still poorly understood. In a previous study, we presented infrared spectroscopic evidence for softening or “liquefaction” of a solid hydrocarbon “model soil” by an aqueous ethoxylated alcohol solution.’ Adsorption of the surfactant onto the hydrocarbon was followed by penetration of the surfactant and water, leading to the formation of a variety of ternary phases at the hydrocarbon-water interface. Upon the formation of such phases, the operation of mechanical as well as emulsification and solubilization processes comes into play, completing the detergency process. In this study of solid oily soil removal, we select tristearin as the “model soil”. Our motivation for studying tristearin stems from the following observations. Tristearin is a commonly encountered component in household laundering (i.e., meat and dairy products; it comprises 85% of fully hydrogenated soybean oil). Like other triglycerides, tristearin exhibits a variety of crystal forms, characterized by differing melting points and acyl chain subcell packing. The disruption of chain packing through the action of a surfactant a t the triglyceride/water interface might thus be expected to be more complex than in the case of a hydrocarbon soil. The effects of surfactants (food grade emulsifiers) on the polymorphism of bulk triglycerides, which have been studied by other techniques, can be compared to the behavior of a layer of tristearin “soil”, which is initially surfactant free, as it interacts with a micellar surfactant solution during the detergency process. Rapid penetration of stearin grease by nonionic surfactants has been reported., The removal of another solid triglyceride (tripalmitin) from chromium and poly(viny1 chloride) surfaces was studied by ellipsometry, in an effort to better understand the removal process a t the molecular level.3 The infrared spectra of triglycerides are con~~~
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(1) Scheuing, D. R.; Hsieh, J. C. L. Langmuir 1988,4, 1277. (2) Cox, M. F. J.Am. Oil Chem. SOC.1986,63, 559. (3) Engstrom, S.; Backstrom, K. Langmuir 1987, 3, 568.
0743-746319012406-0312$02.50/0
siderably more complex than those of hydrocarbons. General band assignments are summarized in Table I. Triglycerides adopt a “tuning fork” type of conformation in the solid state, in which chains one and two form a long, linear chain. Chain three runs perpendicular to them and then bends at the second carbon atom to pack parallel to the other two chains. The variety of crystal forms is determined primarily by the packing of the acyl chains into various subcells and by the packing and orientation of the planes formed by the terminal methyl groups.44 The differences between the three polymorphs of tristearin are summarized in Table 11. The hexagonal subcell packing of the chains in the a form represents the “loosest” form of packing; i.e., it is reminiscent of the lamellar structures of liquid crystals. The planes of the carbon chains, which are extended in an all-trans conformation, are oriented a t random to each other and undergo considerable oscillatory motions along their long axes. X-ray techniques have confirmed that lamellar structures are present just above the melting point of triglycerides,’ indicating a close relationship of the CY form, with its considerable acyl chain disorder, to fully “liquefied” systems such as liquid crystals and melts. The orthorhombic subcell is detectable in the infrared spectra of the p’ form by the “factor-group” splitting of the CH, scissoring and rocking bands. In both the j3 and p’ forms, the acyl chains are tilted relative to the planes formed by the terminal methyl groups.‘ There are apparently a variety of 0 forms possible, which differ in the angle of tilt of the acyl chains.‘ The triclinic subcell of the p form can be distinguished from the hexagonal and orthorhombic subcells by shifts in the CH, scissoring, wagging, and rocking bands. The vari(4) DeJong, S.; van Soest, T.C. Acta Crystallogr. 1978, B34, 1570. (5) Hernqvist, L.; Larsson, K. Fette Seifen Anstrichmittel 1982, 84, 9, 349. (6) Precht, D.; Frede, E. Acta Crystallogr. 1983, B39, 381. (7) Aronhime, J. S.; Sarig, S.; Garti, N. J. Am. Oil Chem. SOC.1987, 64, 4, 529.
0 1990 American Chemical Society
Detergency of a Nonionic Surfactant
Langmuir, Vol. 6, No. 2, 1990 313
Table I. General Band Assignments frequency, cm-' assignment C=O stretching, snl carbonyl groups 1736 C=O stretching, sn2 carbonyl 1728 CH, deformation (scissoring) 1471-1467 1456 CH, deformation 1415 CH, deformation, a CH, groups CH, deformation 1390 CH, wagging band progression 1330-1194 C-0 stretching 1180, 1112 Table 11. Characteristics of Tristearin Polymorphs tme melting point, OC acyl chain subcell a 54.7 hexagonal 63 orthorhombic 8' 73 triclinic B ~~
ous 0 forms, however, are apparently indistinguishable.s
Experimental Section Attenuated total reflectance (ATR) spectra of thin tristearin layers on the surface of the internal reflectance element (IRE) were obtained as previously described? Since the water H-OH bending band near 1640 cm-' was always observed immediately upon filling the cylindrical internal reflectance cell (CIRCLE) with water or a surfactant solution, the thickness of the tristearin layers was probably about the same as achieved in earlier studies of hydrocarbon layers, i.e., approximately 1 pm. A standard size (6-mL solution volume) CIRCLE, equipped with a ZnSe IRE, was used (Spectra-Tech). Tristearin layers were deposited on the IRE by using a controlled withdrawal of the IRE from a solution of tristearin in tetrahydrofuran, to yield what we refer to as "solvent cast" layers. Some of the layers were recrystallized by placing the coated IRE in an oven at 85 OC for 10 min and then allowing the IRE to cool freely to room temperature. A Digilab FTS 15/90 spectrometer, equipped with a wideband mercury-cadmium-telluride detector, was employed. Timeresolved spectra were obtained by using the GC-IR data acquisition software available on the Nova 4 computer supplied by Digilab. By adjusting the frequency range of interest to between 2611 and 700 cm-', and adjusting the undersampling ratio to 4, we obtained spectra at a nominal 4-cm-' resolution. The spectral plots presented in this paper were produced by a Digilab 3240 SPC data system, after transfer of the digitized spectra from the Nova 4. Neodol23-6.5 (Shell ChemicalCo.) was used as received. This commercial surfactant contains a mixture of C,, and C,, alcohols with an average ethylene oxide (EO) chain length of 6.5. The detergency experimentsdiscussed below consisted of exposing the tristearin layers to static solutions of the surfactant, since earlier work' had shown that the mechanical action provided by flowing solutions through the CIRCLE caused more rapid removal of the interfacial layer of the ternary surfactantwater-soil phase. The use of static solutions slows the detergency process, making it possible to record a number of spectra during several minutes of rapid soil removal, and enhances detection of the small amounts of interfacial ternary phases formed. Band frequency shifts and widths were determined with a peak-locatingprogram developed by D. J. Moffatt of the National Research Council of Canada. The peak-locating software distributed by Digilab yielded similar trends. The intensity of the CH, band was determined relative to local base-line points established at 1500 and 1430 cm-'. Standard Digilab software was also used in the subtraction of the spectra of liquid water, water vapor, and linear base lines, to facilitate the presentation of the spectra. Interpolation by a factor of 4 was used to facili(8) deRuig, W. G. Infrared Sectra of Monoacid Triglycerides with Some Apptications to Fat Analysis; Agriculture Research Reports 759, Centre for Agricultural Publishing and Documentation, Wageningen, The Netherlands, Thesis, Utrecht University, 1971. (9) Scheuing, D. R. Appl. Spectrosc. 1987, 41, 8, 1343.
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Results and Discussion Removal of Solvent-Cast Tristearin Layer. The slow withdrawal of the IRE from a T H F solution of tristearin would be expected to produce a tristearin layer in which the p crystal form predominates.' A comparison of the spectrum of the solvent-cast layer to published references of 0 tristearin a t 25 "C indicates a close similarity, including the relatively high frequency CH, scissoring band a t 1471.5 cm-l, the general appearance of the CH, wagging band progression, and the C-O stretching bands at 1178.9 and 1112.4 cm-l.' The frequencies of the bands in our interfacial spectra cannot be compared directly to those of published transmission spectra, due to the band distortions inherent to ATR spectroscopy." The frequency shifts observed during detergency runs are, however, still useful in detecting changes in the packing of the tristearin molecules in the layers, especially in the change from one polymorph to another, as discussed further below. Figure 1 compares the spectra of a solvent-cast layer and a recrystallized layer of tristearin on the surface of the IRE. The intensity of the CH, scissoring band is useful for monitoring the removal of tristearin from the IRE surface. Figure 2 shows the changes in the band intensity during exposure of the solvent-cast layer (primarily 0 phase) and the recrystallized layers (primarily a phase) to a 0.03% Neodol 23-6.5 solution. The removal is initially very rapid but slows a t longer times, in agreement with the trends found for the removal of eicosane' and the removal of tripalmitin from PVC surfaces, as monitored by ellip~ometry.~ The difficulty of extracting quantitative layer thicknesses (quantitative removal rates) from the band intensities has been discussed earlier' and is due to the continuous change in the relative thickness of the optically distinct tristearin and water "layers" a t the interface, which results in some uncertainty in the refractive index of the interfacial layer and the sampling depth of the infrared radiation and hence complicates a calculation of tristearin thickness during the detergency runs. Figure 3 indicates that the frequency of the scissoring band increases slightly during the removal process. This (10) Harrick, N. J. Internal Reflection Spectroscopy; Interscience Publishers: New York, 1967.
314 Langmuir, Vol. 6,No. 2, 1990 I
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1
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Figure 3. Frequency of the CH,deformation band in the timeresolved spectra during detergency runs. The increases in frequency of the band in the spectra of the recrystallized layers exposed to Neodol 23-6.5 indicate acceleration of the (Y to fi crystal transformation, compared to that which occurs in water only. The initially higher frequency of the band in the spectra of the solvent-cast layer indicates the presence of primarily /3 phase: run 1, thinner recrystallized layer; run 2, thicker layer. V b
change suggests an increase in the ordering of the acyl chains of the tristearin molecules on the surface of the IRE. Earlier work’ with eicosane as the “model soil” showed that a decrease in ordering (decrease in frequency of the CH, band) of the methylene chains accompanied the removal by Neodol 23-6.5. There does not appear to be a significant increase in the interfacial concentration of “disordered” or “liquefied” tristearin upon interaction with this surfactant. The spectroscopic changes can be interpreted as evidence for the selective removal of “disordered” (aphase or amorphous) tristearin, leaving the more highly ordered, higher melting /3 phase on the IRE surface. Other changes in the time-resolved spectra (Figure 4) of a solvent-cast layer include a narrowing and shift of the CH, deformation band and a narrowing and shift to higher frequency of the C-0 bands near 1179 and 1112 cm-’. Several of the CH, wagging bands shift in frequency and/or broaden very slightly during the 60-min detergency experiment. Difference can also be used to enhance (11) Kawai, T.; Umemura, J.; Takenaka, T.; Gotou, M.; Sunamoto, 1988, 4, 449. (12) Nakaahima, N.; Yamada, N.; Kunitake, T.; Umemura, J.; Takenaka, T. J. Phys. Chem. 1986,90,3374. (13) Mantsch, H. H.; Cameron, D. G.; Tremblay, P. A.; Kates, M. Eiochim. Biophsy. Acta 1982,689,63. (14) Mantsch, H. H.; Martin, A.; Cameron, D. G. Biochemistry 1981,20,3138. (15) Cameron, D. G.; Casal, H. L.; Mantsch, H. H. Biochemistry 1980,19,3665. (16) Umemura, J.; Cameron, D. G.; Mantsch, H. H. Biochim. Biophys. Acta 1980,602, 32.
J. Langmuir
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Figure 5. Time-resolved difference spectra of solvent-cast tristearin layer exposed to 0.03% Neodol 23-6.5. The spectrum of the initial, dry layer has been subtracted from spectra obtained at times indicated. The shift in the CH, deformation band toward higher frequency results in the distorted band shape. The CH deformation band near 1393 cm-’ indicates a perturbation otthe packing of the terminal methyl groups of tristearin. The appearance of the CH wagging bands indicates that crystalline tristearin, which can2be assigned to the fl phase, is incompletely removed at long exposure times. Evidence for the absorption of Neodol23-6.5 is the broad band between 1140 and 1070 cm-’, due to C-0stretching of ethylene oxide groups, beneath the sharper C-0 bands of tristearin near 1110 and 1105 cm-l. the detection of small spectroscopic changes. Figure 5 shows a series of difference spectra, obtained by subtraction of the spectrum of the layer a t 0.1-min of exposure from those obtained at later times. Cumulative spectroscopic changes in the layer, induced by interaction with Neodol 23-6.5,will be enhanced in the difference spectra. The “differential” shaped CH, scissor band near 1471 cm-l confirms the gradual shift of this band toward the higher frequency mentioned above. The appearance of the CH, deformation band and the CH, wagging bands in all the difference spectra indicates continuing changes in the packing of the acyl chains with exposure time. The only evidence for adsorption of the surfactant is the broad absorbance between 1140 and 1070 cm-’, which could be due to the intense C-0 stretching of the ethylene oxide moieties in the surfactant head group.’
Langmuir, Vol. 6, No. 2,1990 315
Detergency of a Nonionic Surfactant
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We now turn to a discussion of another important band, the C=O stretching band of the ester carbonyl groups.17 This band, which is comprised of a t least two components, appears to shift toward lower frequency during the detergency run. A more detailed analysis of the carbonyl band is warranted because of the sensitivity of the band to hydrogen bonding and conformational effects. The interpretation of the thermally induced changes in phospholipid bilayers, for example, relies on studies of the ester carbonyl band.14718 Fourier self-deconvolution of the broad carbonyl bandlg reveals that it is comprised of three components near 1743, 1736, and 1728 cm-' (Figure 6). The apparent frequency shift of the two overlapping bands in the original spectra during the detergency run is due to changes in the relative intensity of the bands a t 1736 and 1728 cm-', which do not shift in frequency significantly. The loss of intensity for the 1736- and 1743-cm-' bands is due to a reduction in the broad component which underlies the sharper peaks. This broad component can be assigned to the fraction of the a-phase polymorph in the solvent cast layer by comparison with the broad band obtained in the spectrum of a recrystallized layer, which is composed primarily of a phase. The time-resolved spectra of the solvent-cast layer in the carbonyl region confirm the interpretation that the @ polymorph is resistant to removal, while the more disordered a phase is rapidly and preferentially removed during the detergency process. The carbonyl bands also suggest that there is little buildup of an interfacial layer of disordered tristearin molecules hydrogen-bonded to surfactant or water. Carbonyl groups involved in hydrogen bonding would be expected to yield bands shifted to significantly lower frequency, i.e., near 1715 cm-', as have been observed in the spectra of compatible blends of polymers stabilized by hydrogen bonding between ester and (17) Mushayakarara,E.; Levin, I. W. J. Phys. Chem. 1982,86,2324. (18) C a d , H. L.; Mantsch, H. H. Biochim. Biophys. Acta 1983, 735,387. (19) Mantach, H. H.; Moffat, D. J.; Casal, H. L. J . Mol. Struct. 1988,173,285.
hydroxyl groupsm or in the spectra of fully hydrated phosphatidylcholine Removal of RecrystallizedTristearin Layers. The influence of the nature of the tristearin polymorph on the detergency process was investigated with a series of experiments employing layers of a tristearin, obtained by recrystallization from the melt of solvent-cast layers, prepared in the usual manner. A monotropic transformation from the thermodynamically unstable a form to the @ form can occur in the solid state below the melting point of the a form, a process known as triglyceride The activation energy for this process is high a t 25 "C, and thus the a to @ transformation of tristearin is very slow near room temperature. At higher temperatures, the number of dislocations in the crystal lattice inceases, which facilitates the conformational changes necessary to accelerate the tran~formation.~ "Aging" of an a tristearin layer was very slight after 24 h of exposure to air a t 25 "C, as indicated by very small spectroscopic changes. Difference spectra obtained by subtraction of the spectrum of the layer obtained immediately after cooling from the spectra recorded 1, 2, 3, and 24 h later revealed shifts in the CH, scissoring and wagging bands and the CH, and C-0 bands as well. The bands appearing in the difference spectra were consistent with @-phaseformation. The a to @ transformation in a layer of tristearin is accelerated by exposure to surfactant-free water a t 25 "C. The CH,, CH,, and C-0 bands, as well as the carbonyl band, all exhibit detectable shifts in the original and difference spectra recorded over a 2-h exposure time. Figure 3 shows that a gradual increase in the frequency of the CH, scissoring band is detectable, indicating the a to @ transformation. The lack of any significant change in the intensity of the band (Figure 2) indicates that exposure to water does not result in significant removal from the IRE,even though a crystal transformation occurs. The changes in the carbonyl band also indicate @-phase formation. The initially broad band characteristic of the a phase develops into the sharper multiplet characteristic of the /3 phase, resembling that observed in the spectra of the solvent-cast layers. The changes observed in the other bands are summarized in Table 111. The removal of a tristearin by a 0.03% Neodol23-6.5 solution is very rapid, as shown in Figure 2. This observation is consistent with the interpretation, based on the results obtained with the solvent-cast layers rich in @ phase, that it is the a phase, with its more disordered acyl chains and ester groups, which is most easily removed from the tristearin layer. However, Figure 3 also indicates that a rapid shift in frequency of the CH, scissoring band occurs during the first several minutes of exposure. The band changes from a singlet near 1467.6 cm-' to a broad doublet as the component near 1472 cm-' increases in relative intensity. At longer times, the band narrows as the component near 1472 cm-' becomes the dominant band, and the removal process slows. Other spectroscopic changes which occur within 5 min include the development of a shoulder at 1392 cm-' on the CH, deformation band, the splitting of the 1312-cm-' CH, wagging band into two components, (20) 255. (21) (22) 128. (23)
Coleman, M. M.; Painter, P. C. Appl. Spectrosc. Reu. 1985,20, Cameron, D. G.; Mantach, H. H. Biophys. J. 1982,34175. Whittam, J. H.; Rosano, H.L. J. Am. Oil Chem. SOC.1975,52,
Azoury, R.; Aronhime, J. S.;Sarig, S.; Abrashkin, S.; Mayer, I.; Garti, N. J. Am. 011 Chem. SOC.1988,65,964.
316 Langmuir, Vol. 6, No. 2, 1990
Scheuing
Table 111. Band Shifts (Frequency, cm-*) in Spectra of Recrystallized Tristearin Layers Indicating a to @ Transformation in air in water in 0.03% Neodol 23-6.5 assignment initial a t 24 h initial at 2 h initial at 5 min CH, CH, CH, CH, CH, C-0 C-0
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10
20 30 40 TIME (MlhL'TES)
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Figure 8. Changes in the width at three-quarters height of the CH, deformation band of tristearin in time-resolved spectra. The spectra of the solvent-castlayer exhibit a band which is initially narrower and decreases slightly during removal, indicating the persistence of the highly ordered j3 phase at the interface. The spectra of recrystallizedlayers exhibit a broader band due to the (Y phase. The recrystallized layer exposed to water only undergoes slight broadening, consistent with the production of some fi phase during "aging"; i.e., the higher frequency CH, band of the p phase appears as a shoulder which broadens the band. The rapid increase in bandwidth in the two detergency runs with recrystallized layers, which is correlated with the shift in frequency and the rapid removal, indicates the acceleration of the a to transformation and the preferential removal of the a phase, leaving a narrow CH, band, characteristic of the more ordered B phase, at longer exposure times. f ~ r m a t i o n .The ~ effect was attributed to enhancement of defects in the a-phase crystal lattice by surfactants which were unable to form mixed crystals with a tristearin. As mentioned above, crystal lattice defects enhance the solid-solid transformation rate. NMR studies24 of bulk tristearin containing small amounts of surfactants have shown that the loose packing of the a phase can readily accommodate surfactant molecules. The T1 relaxation times of a tristearin were unaffected by added surfactant. After transformation to the @ form, however, the T1 values were lowered significantly by the presence of surfactant. The incorporation of surfactant was thought to cause the formation of vacancies between the methylene chains of neighboring tristearin molecules of the @ form. These vacancies enhanced the mobility of tristearin molecules, particularly near the terminal methyl groups. The detergency results we have obtained are consistent with these studies of bulk tristearin. The adsorption and penetration of Neodol 23-6.5 (and water) into the a phase should readily occur, and due to the loose packing of the a phase, little additional disordering of the tristearin molecules would be detected. The preferential removal of the a phase would be the result of the rapid penetration of even a low level of surfactant. At the same time, however, the presence of penetrating surfactant would accelerate the solid-solid a to @ tranformation, due to the enhancement of defects in the lattice by Neodol 23-6.5, a liquid surfactant with little ability (24) Raney, K. H.; Benton, W. J.; Miller, C. A. J. Colloid Interface Sci. 1987, 117,282.
Langmuir 1990,6, 317-322 to cocrystallize with tristearin. The formation of @ phase in the layer, even 0 phase containing some surfactant molecules, causes a considerable change in the “soil” surface presented to the aqueous surfactant solution. The changes in the packing of the methylene chains, ester groups, and the terminal methyl groups, which we have detected spectroscopically, result in a reduced rate of surfactant penetration. Thus, in the case of a tristearin layer rich in CY phase, removal by Neodol23-6.5 is rapid, but transformation to the p phase is also accelerated by the very same process of surfactant and water penetration. In the case of the solvent-cast layers, rich in @ phase, a preferential removal of the a phase is indicated. The formation of “liquefied” tristearin-water-surfactant phases from the @ phase is much slower than from the CY phase and is also much slower than the removal of “liquefied” tristearin from the interface by solubilization or emulsification processes. The @-phasecontent of the layer will thus increase with exposure time, regardless of the initial layer composition. Incomplete removal of tristearin is a consequence of the surfactant-mediated increase in the amount of stable fl form a t the interface.
Conclusions An FT-IR method for obtaining time-resolved spectra of a “model soil” interacting with an aqueous surfactant solution has been applied to a study of tristearin and an ethoxylated alcohol, Neodol 23-6.5. The spectroscopic
317
changes observed are dominated by tristearin crystal structure polymorphism. The CY phase of tristearin is readily removed from the surface of the IRE, without an extensive increase in an interfacial layer of “liquefied” soil-water-surfactant. Neodol 23-6.5 accelerated the CY to @ phase transformatioin of tristearin, apparently a t very low interfacial concentrations. The formation of @ phase is evidence for the rapid, preferential adsorption and penetration of a t least a small amount of the surfactant into the layer of a tristearin during the detergency process. The CY to @ transformation of tristearin impedes the detergency process, since the latter is the most ordered, highest melting polymorph possible. Even after 2 h of exposure, /3 tristearin remains on the IRE surface. The detergency of solid triglycerides is thus found to be even more complex than that of a solid hydrocarbon “model soil” studied previously. A determination of the phase diagram of tristearinwater-Neodol23-6.5 will aid in an understanding of the interactions possible between these materials. As this study has shown, the application of concepts such as the ternary “phase inversion temperature” 24 in characterizing these interfacial phenomena will be kinetically complicated by the changes in the nature of the interface itself. FT-IR appears to be a useful tool for studying those changes. Registry No. Tristearin, 555-43-1.
Effect of Isomeric Alcohols as a Minor Component on the Adsorption Properties of Aqueous Sodium Alkyl Sulfate Solutions D. Vollhardt* and G. Czichocki Central Institute of Organic Chemistry of the Academy of Sciences of GDR, Rudower Chaussee 5, Berlin, 1199, GDR Received February 16, 1989.In Final Form: June 13, 1989 The effect of known trace amounts of the highly surface-active alcohols decan-1-01, dodecan-1-01,and 2-ethyldecan-1-01on the equilibrium surface tension-concentration isotherms of aqueous solutions of sodium decyl sulfate (SDS)and sodium dodecyl sulfate was systematically studied. For this particular system, the complex adsorption parameter data of Frumkin’s surface equation of state were calculated. On the basis of the generalized Szyszkowski equation, the surface activity parameters ( a l , a ) of the main and minor component were calculated. By use of the free energy of adsorption, the atsorption behavior of the two-component system with two homologous series of surfactants was characterized. The surface activity parameter values calculated for the sparingly soluble alcohols as minor component and the effect of chain branching on the adsorption properties seem to be reasonable.
Introduction Much of the interest in the well-known sodium alkyl sulfates stems from their potential in a wide range of scientific and technological applications. In recent years, we have obtained new information on the significant effect of trace quantities of surface-active contaminanh on the adsorption properties of sodium alkyl sulfates.’?’ So far, most of the papers published on this 0743-7463/90/2406-0317$02.50/0
subject have focused on the sodium alkyl sulfate @AS)(RoH) system.3-5 (1) Czichocki, G.; Vollhardt, D.;Seibt, H. Tenside Detergents 1981, 18,320. (2) Mysels, K. J. Langmuir 1986, 2, 423. (3) Vijayendran, B. R. J. Colloid Interface Sci. 1977,60,418. (4) Smith, A. J. Colloid Interface Sci. 1978, 66, 575. (5) Roeen, M. J. J.Colloid Interface Sci. 1981, 79, 587.
0 1990 American Chemical Society
