Langmuir 1986,2, 170-173
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Phase Behavior of Ternary Systems: H20-Oil-Nonionic Amphiphile with n -Alkyldimethylphosphine Oxides K.-H. Pospischil Max-Planck-Institut fuer Biophysikalische Chemie, 0-3400 Goettingen, West Germany Received August 20, 1985. I n Final Form: November 5, 1985 This paper reports on studies of the phase behavior of ternary systems H20-oil-CiDMPO (i = 10, 12, 14), where CiDMPOstands for n-alkyldimethylphosphine oxides. The systems show a phase behavior very similar to that with n-alkyl polyglycol ethers (CiEj) previously reported in the literature. This also holds if a lyotropic (NaCl) or hydrotropic (SDS) salt is added. With respect to application, these amphiphiles appear to be more efficient than CiEj in that the three-phase temperature intervals are somewhat wider and the minimum concentration of amphiphile needed to prepare homogeneous solutions of equal masses of HzO and oil is somewhat lower.
I. Introduction In a series of papers, Kahlweit and co-worker~l-~ have reported on the phase behavior of ternary systems of the class H,O-oil-nonionic amphiphile with n-alkyl polyglycol ethers (C,Ej) as amphiphiles. As they have shown, the phase behavior of these systems is mainly determined by the interplay of the two binary diagrams H,O-C,E, and oil-C,E,. This raises the question whether the general features of this interplay also hold for other classes of nonionic amphiphiles. C,E, molecules have tentacle-like hydrophilic groups, which makes it difficult to visualize their arrangement on the molecular level, in particular, with respect to the effective diameter of their head groups. For this reason we have studied the phase behavior of ternary systems with n-alkyldimethylphosphine oxides C,H,,+,P(O)(CH,),, in the following abbreviated as C,DMPO, as amphiphiles which have a more compact and, furthermore, rather rigid head group, in order to compare their effect with that of C,E,. The latter property of the C,DMPO molecules may be of interest when discussing the various models for "microemulsions" which are based on the assumption of an interfacial layer of the amphiphile separating bulk phases of H 2 0 and oil, respectively. 11. Experimental Section
CiDMPOwas synthesized following the procedure published by Hays.6 The products were recrystallized twice from acetone, thereafter from n-hexane,and once again from acetone. The yield for C,,DMPO was 56% (Hays reported 71-85%) with a melting point of 82.5 "C (Laughlin7reported 84-85 "C). The yield for C,,DMPO was 49% (Hays, 68%) with a melting point of 85.7 "C (Laughlin,89-90 OC). The oils were commercial products (Merck) and applied without further purification. The lyotropic mesophases show the same characteristictextures as the amphiphiles CiEj.The regions of the phases were determined by observing test tubes through crossed polarizers;in some
occurrence of anisotropy with either rising or dropping temperature.
111. Binary Phase Diagrams H,O-C,DMPO and Oil-C,DMPO The phase diagram of the binary system H,O-C,DMPO shows the same general features as that of the system H,O-C,E,. Both systems show an upper loop (24), the LCST To of which drops, as one would expect, with increasing i (with C,E,, a t constant j ) . Figure 1 shows the phase diagrams of the system Hz0-C12DMP08*9 (left) and of H20-C1,DMP010 (right). The diagram with C1,DMPO ( T p= 40 "C) looks similar to that of H20-C,2E611( T , = 48 "C). With C14DMP0,T plies around 15 "C, the upper loop here overlapping with the solubility of (solid) C,,DMPO in water. Furthermore, the lamellar mesophase L , extends deeply into the upper loop at elevated temperatures, leaving only a rather narrow region of homogeneous isotropic solutions (14). The phase diagrams of the binary systems oil-amphiphile contrast. The UCST T, of the (lower) oil-C,E, gap lies, in general, close to the melting point of the mixture, rising steeply with addition of water. With C,DMPO, on the other hand, the solid substance is almost insoluble in oil up to temperatures close to the boiling point of the mixture (see, e.g., Figure 9 in ref 10). However, as can be seen on Figure 3 of this paper, the solution temperature of the solid drops rather steeply with the addition of water, so that in the presence of about 5 wt % H,O one finds a lower miscibility gap between two liquid phases on the oil-rich side, the UCST T, of which again rises steeply with further addition of water. It is this liquid miscibility gap that in interplay with the upper H,O-C,DMPO loop determines the phase behavior of the ternary system. Accordingly, one expects a phase behavior with the same general features as with C,E, as amphiphile.
cases the morphology was identified by using a polarizing mi-
croscope with hot stage. These mesophases are, in general, surrounded by narrow regions of coexistence with a neighboring phase. Due to the difficulty of determining the exact position of the boundaries, the data points on the figures show the first (1)Kahlweit, M. J . Colloid Interface Sci. 1982, 90, 197.
(2) Kahlweit, M.; Lessner, E.; Strey, R. J. Phys. Chem. 1983,87,5032; 1984,88, 1937. (3) Kahlweit, M.; Strey, R.; Haase, D. J. Phys. Chem. 1985, 89, 163. (4) Kahlweit, M.; Strey, R.; Firman, P.; Haase, D. Langmuir 1985, I , 281. (5) Kahlweit, M.; Strey, R.; Firman, P. J. Phys. Chem., submitted for
publication. (6) Hays, H. R. J . Org. Chem. 1968, 33, 3690. (7) Laughlin, R. G. J . Org. Chem. 1965, 30, 1322.
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IV. The System H,O-n -Octane-C,,DMPO The most convenient procedure to study the phase behavior of a ternary system is to cut a vertical section through its phase prism, erected on the center line of the Gibbs triangle, i.e., on the line connecting the point H,O/oil = 1:l on the H,O-oil side with the C,DMPO (8) Hermann, K. W.; Brushmiller, J. G.; Courchene, W. L. J . Phys. Chem. 1966, 70, 2909. (9) More recent determinations by: Lang, J. C.; Morgan, R. D. J . Chem. Phys. 1980, 73, 5849. (10) Laughlin, R. G. Adu. Liq. Cryst. 1978, 3, 41. (11)Mitchell, D. J.; Tiddy, G. T. J.; Warring, L.; Bostock, Th.; McDonald, M. P. J . Chem. SOC.,Faraday Trans. 1 1983, 79, 975.
0 1986 American Chemical Society
Langmuir, Vol. 2, No. 2, 1986 171
.
0
0
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-
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Figure 1. Phase diagram of the binary systems H20-C12DMPO (left) and H20-Cl4DMPO (right). 100 I
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Figure 2. Vertical section through the phase prism of the system HzO-n-octane-ClzDMPO (HzO/oil= 1:l). corner.5 Such a section shows the profile of the body of heterogeneous phases, the section through the three-phase body (if present) floating within that body like a “fish”, and the regions of existence of the lyotropic mesophases at higher concentrations of the amphiphile. Figure 2 shows this section for the system H,0-n-octane-C12DMP0. One finds, as expected, a three-phase body (34) between T I = 67.0 “C and Tu= 93.5 “C, with a ”tail” at about 15.2 wt % C12DMPO. Compared with the phase diagram of the binary system (Figure 1, left) the lamellar mesophase L, has grown toward lower ClzDMPO concentrations, pointing a t the three-phase body like a signboard, as in the system with long chain CjE,.5 Also, the lower boundary of the threephase body and its continuation as lower boundary of the upper two-phase region (24) has a similar shape as the lower boundary of the upper H20-CI2DMPO loop, shifted to somewhat higher temperatures. The body of heterogeneous phases shows a pronounced “Schreinemakers’ g r o ~ v e at ” ~the “tail” of the three-phase body. This suggests cutting another vertical section through the phase prism erected on a line parallel to the H20-oil side at the concentration of the amphiphile in that groove. This section is shown on Figure 3 (top). Again one finds a narrow channel of an optically isotropic, often strongly scattering homogeneous phase from the water-rich to the oil-rich side, ascending temperaturewise with increasing oil concentrations as the “waist” around the body of heterogeneous phase^.^ This channel permits a study of the microstructure of the homogeneous solution as it changes from an o/w to a w/o “emulsion”. Finally, we have studied the effect of a lyotropic (NaC1) and a hydrotropic (SDS) salt on the phase behavior. In the bottom of Figure 3 one can see the same section as on the top, pure H,O being replaced by a 10 wt % NaCl solution. As with C,E,, this lowers the three-phase body and thus the groove temperaturewise (see Figure 10 in ref
0’ 0 10 20 30 LO 50 50 70 80 90 100 lO%NaCI In H20/C,,DMP0 n-Octone/C,,DMPO 83 5 165 wi% 8 3 5 15 5
-
Figure 3. (Top)Vertical section through the phase prism of the system H20-n-octane-C12DMP0at constant C12DMP0concentration (16.5 wt %). (Bottom) Same section with 10% NaCl solution instead of pure HzO.
1
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20
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Figure 4. Vertical section through the phase prism of the system HzO-n-octaneC12DMP0 (HzO/oil = 1:l)with 0.1% SDS solution instead of pure HzO (to be compared with Figure 2). 5) and makes the regions of existence of the lyotropic mesophases grow (see Figure 15 in ref 3). The tail of the fish, i.e., the minimum mass of the amphiphile, cmh,needed to prepare a homogeneous solution of equal masses of H,O and oil, is shifted toward lower concentrations with increasing NaCl concentration: With octane, e,,, decreases almost linearly from 15.2 w t % CIzDMPO for pure HzO to 8.2 wt % for a 20 w t % NaCl solution instead of pure HZO. The addition of a hydrotropic salt like SDS, on the other hand, makes the three-phase body shrink and rise temperaturewise (see Figure 10 in ref 5), until at a sufficiently high SDS concentration, the three-phase body may disappear altogether at a tricritical point. Figure 4 shows the section along the center line of the (pseudoternary) phase prism with a SDS concentration above that concentration, namely, 0.1 w t % SDS in H 2 0 (to be compared with Figure 2; note the different scales on the abcissa). The threephase body has disappeared, and the groove now extends
172 Langmuir, Vol. 2, No. 2,1986 1001
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0 5 10 15 20 25 30 H,O/Toluene 1 1 C,,DMPO Figure 6. Vertical sections through the phase prisms of the systems H,@oilX,@DMPO (H,O/oil= 1:l) with toluene, xylene, and mesitylene as oils.
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as a narrow channel toward the H,O-oii side down to about 3 wt % CIZDMPO. This effect, which is an instructive example for the "synergism" of nonionic and ionic amphiphiles, has also been observed with C,E, as amphiphile, e.g., in H&ndecane-C8E4-SDS (0.1 wt % in HzO). V. The System H2O-n-Alkane-Cl4DMPO With this system we have studied the dependence of the position and extensions of the three-phase body on the hydrophobicity of the oil, expressed in terms of the carbon number k of n-alkanes. Figure 5 shows the fishes for k = 8,10,and 12. As with C,EJ as amphiphile, the three-phase body rises and widens with increasing carbon number, the three-phase temperature interval AT = (2'. - TI), thus shaping a cusp if plotted vs. k (see Figure 4 in ref 5). The data are summarized in Table I. The first column gives the carbon number of the n-alkane, the following two TI and Tu.The fourth column gives the mean temperature of the three-phase interval T = (T, + Tu)/2, the fifth the
concentration of the amphiphile (in wt %) a t the tail of the fish. The last three columns give the mole fractions of H,O and C,DMPO at this p i n t of the phase prism and the ratio between them; i.e., the number of H20 molecules solubilized by each C,DMPO molecule. If compared with Figure 9 in ref 5, one fmds a similar dependence of and the molar ratio on k as with the system H,O-n-alkaneC8E,. We further note that in the system with n-octane c,,,," decreases from 3.6 wt % C,,DMPO for pure H,O to 1.7 wt % with a 20 wt % NaCl solution instead of pure H20.
VI. Summary The results of these studies show that the phase behavior of the temary system H,O-oil-C,DMPO is quite similar t o that with C,EJ as nonionic amphiphile. C,DMPO appears to be more efficient than C,EJ insofar as the minimum concentrations of amphiphile needed to prepare a homogeneous solution of equal masses of H20 and oil are somewhat lower than with long-chain C,E,, and the three-phase temperature intervals are somewhat wider. The latter property, in particular, makes the shorter chain C,DMPO suited for studying the phase behavior of temary systems with less hydrophobic oils like cyclic alkanes or aromatics. Figure 6 shows the sections through the three-phase bodies of H,0-oil-Cl&MP012 with toluene, xylene, and (12) For the phase d w a m of the binary system H&C,DMPO,
ref 8 and 9.
see
Langmuir 1986, 2, 173-178 mesitylene as oil, respectively. As expected, the position of the fishes on the temperature scale rises with increasing hydrophobicity of the oil, the fish for benzene being located below the melting point of the mixture. The comparison of these fishes with that for the quinary system HzOtoluene-C,Eo-SDS-NaC1 (represented in a pseudoquaternary phase tetrahedron in Figure 11 in ref 3) demonstrates that the nonionic CloDMPO is even more effective with respect to increasing the mutual solubility between H20and aromatics than that of a combination of butanol and SDS. An addition of NaCl will merely lower the position of the fishes on the temperature scale (see Figure 3). On the other hand, the three-phase bodies of the ternary systems are restricted to a temperature interval of about 10 deg, whereas that of the quinary system (at the particular ratio SDS/C4Eo= studied by Bellocq et
173
al.13) extends from the melting to the boiling point of the mixture. Finally, we note that the phosphorus nucleus 31P is well suited for NMR studies. This work is in progress.
Acknowledgment. This work was carried out in the laboratory of Prof. M. Kahlweit. I am indebted to him and to Dr. R. Strey for suggestion of the problem and advice with the experiments. I am further indebted to D. Luckmann for drawing the figures. Registry No. CloDMPO, 2190-95-6; C,,DMPO, 871-95-4; C14DMP0,2190-96-7; SDS, 151-21-3;NaC1, 7647-14-5; octane, 111-65-9;decane, 124-18-5;dodecane, 112-40-3;toluene, 108-88-3; mesitylene, 108-67-8;xylene, 1330-20-7. (13) Bellocq, A.; Biais, J.; Clin, B.; Gelot, A.; Lalanne, P.; Lemanceau, B. J. Colloid Interface Sci. 1980, 74, 311.
Adsorption Interference in Mixtures of Adsorbate Gases Flowing through Activated Carbon Adsorber Beds Richard Madey,* Panos J. Photinos, and Daniel Rothstein Department of Physics, Kent State University, Kent, Ohio 44242
Robert J. Forsythe Broome Community College, Binghamton, New York 13902
Jan-Chan Huang Department of Plastics Engineering, University of Lowell, Lowell, Massachusetts 01854 Received June 27, 1985. I n Final Form: November 6, 1985 We studied adsorption interference in several binary mixtures and one ternary mixture of adsorbate gases in a helium carrier gas flowing through activated carbon adsorber beds at 25 O C . Interference is manifested by a reduction of the adsorption capacity of each component in the mixture from the value for a pure adsorbate and an outlet concentration greater than the inlet concentration for the weaker adsorbing component until the stronger adsorbing component elutes. No interference effects were seen when both components of the mixture exhibit linear isotherms. The magnitude of the interference depends on the adsorption capacities and relative concentrations of the two components in the mixture.
Introduction The measurement and interpretation of the dynamic behavior of binary mixtures are necessary to the understanding of the adsorption and transport of multicomponent mixtures. Most practical applications of the adsorption process involve the transport of mixtures of several adsorbable gases. The application of gas adsorption on solid adsorbents to separate a component from a gas mixture requires knowledge of two general subjects: (1) the physicochemical properties of the gas-solid interaction, particularly adsorption isotherms of the various components, and (2) the dynamic behavior of the key gas components in the separation device. Three diffusion processes are important in the transport of a gas through a porous medium: longitudinal diffusion in the gas phase, mass transfer through the film a t the gas-solid interface, and solid-phase diffusion within the adsorbent particles. These three processes are characterized by coefficients DL, k F , and D,, respectively. The differential equations for the isothermal adsorption of an absorbate gas in an inert carrier gas are
and
Here C is the gas-phase concentration, u is the interstitial flow velocity, t i s the void fraction of the adsorber bed, q is the adsorbed-phase concentration, and Q is the adsorbed-phase concentration averaged over the volume of the adsorbent particles. For spherical particles, of radius
R, 3
Q = R3 - l R q0( r , z , t ) r 2 dr
The introduction of an average concentration eliminates the radial dependence of the solid-phase concentration from eq 1. The differential equation relating q and C is1
(4) Equations 1-4 contain two dependent variables C and q (1) Lapidus, L.; Amundson, N. R. J. Phys. Chem. 1952,56, 373.
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0 1986 American Chemical Society
