J. Phys. Chem. 1985,89, 2657-2661 lization process as well as plastize the polymer chain, which have made all the molecular motions p i b l e . Moreover, the completion of the crystallization is found to be related to the density of the swelling solvent. This is probably due to the strong solubilization effect of the solvent toward the dye or to the density effect on the mobility of the polymer chain, which affects the dye motions in the crystallization step, in polymer matrices swollen by highdensity (p 5 1 g/cm3) solvents.
Acknowledgment. I thank Dr. W. Prest for suggestion of the three-component solubility parameter analysis, Dr. D. J. Williams
2657
for comments on the manuscripts, and Professor Uyeda for bringing our attention to references on the subject of stepwise recrystallization. Registry No. (r-bu)VOPC, 96164-79-3;(t-bu),VOPC, 95552-15-1; vinyl chloride-vinyl acetate copolymer, 9003-22-9; methylene chloride, 75-09-2; chloroform, 67-66-3; 1,l-dichloroethane,75-34-3; 1,2-dichloroethane, 107-06-2; 1,1,2-trichloroethane,79-00-5; 1,l,l-trichloroethane, 71-55-6; benzene, 71-43-2; toluene, 108-88-3;xylene, 1330-20-7; chlorobenzene, 108-90-7;acetone, 67-64-1;2-butanone, 78-93-3; 3-pentanone, 96-22-0;ethyl acetate, 141-78-6;tetrahydrofuran, 109-99-9; 1,Cdioxane, 123-91-1; 2-propanol, 67-63-0; methanol, 67-56-1.
Binding Interactions of Tetrahedral Ions in Aqueous Surfactant Solution Keith Radley and Alan S. Tracey* Department of Chemistry, Simon Fraser University, Burnaby, British Columbia, Canada V5A IS6 (Received: August 29, 1984; In Final Form: December 1 1 , 1984)
The tetrahedral ions NH4+,N(CH3)4+,Clod-, and BF, contained in lyotropic liquid crystalline medium have been investigated by NMR techniques. The liquid crystalline systems employed were those prepared from mixed detergent systems of either potassium dcdecanoate/alkyltrimethylammoniumbromide or potassium N-hexadecanoyl-I-prolinate/alkyltrimethylammonium bromide. Information concerning the binding of these ions to the amphiphileswas obtained. It was found that in the dcdecanoate mesophase the ammonium ion was held in the micellar interface by binding to three amphiphiles, and the results also indicated that ammonium was held about as strongly as alkali-metal ions. Tetramethylammonium ion was held only weakly by its binding interactions, and the results were consistent with diffuse binding of this ion. Perchlorate was found to bind to three tetradecyltrimethylammonium amphiphiles in the dodecanoate system but to only two in the prolinate system. Chloride was found to behave similarly. It was suggested that this latter behavior occurred because of the large increase in salt concentration (about a factor of 10) on going from the dodecanoate to the prolinate system. Like perchlorate, the boron tetrafluoride ion was found to bind to three trimethylammonium head groups under conditions corresponding to the dodecanoate/alkyltrimethylammoniummixed mesophase system.
Introduction The interactions between monatomic ions and amphiphilic materials have been the subject of many the~reticall-~ and experimental investigations.k8 Relatively little work has been reported concerning the binding interactions of tetrahedral polynuclear species although a study of the interactions of ammonium and tetramethylammonium ions in the anisotropic aqueous ammonium octanoate systems has been reported9 as has binding in polyelectrolyte s o l ~ t i o n . ~Of major importance in understanding the binding of ions is a knowledge of the number of amphiphiles that a counterion is associated with in its bound state and whether only one type of binding does.occur. Information concerning the nature of the binding interactions is of predominate interest as is that concerning ion competition for binding sites. It has been shown that considerable information concerning ion behavior can be obtained by observing the quadrupole splittings (1) Evans, D. F.; Ninham, B. W. J. Phys. Chem. 1983,87, 5025-5032. (2) Beunen, J. A.; Ruckenstein, E. J . Colloid Interface Sci. 1983, 96, 469-487. (3) WennerstrBm, H.; Lindblom, G.; Lindman, B. Chem. Scr. 1974, 6, 97-1 03. (4) Delville, A.; Laszlo, P. Biophys. Chem. 1983, 17, 119-124. ( 5 ) Stilbs, P.; Lindman, B. J. Magn. Reson. 1982, 48, 132-137. (6) Larsen, J. W.; Magid, L. J. J . Am. Chem. SOC.1974,96, 5774-5782. (7) Tracey, A. S.; Boivin, T. L. J . Phys. Chem. 1984, 88, 1017-1023. (8) Tracey, A. S . Can. J . Chem. 1984, 62, 2161-2167. (9) Persson, N.-0.; Lindman, B. Mol. Cryst. Liq. Cryst. 1977, 38, 321-344.
0022-3654/85/2089-2657$OlSO/O
from ions with a quadrupolar nucleus when those ions are contained in an anisotropic medium. Particularly suitable materials for such studies are the nematic lyotropic liquid crystalline materials prepared from the potassium dodecanoate/alkyltrimethylammonium bromide/decanol/electrolyte/water mixed detergent system. The advantage of this system lies mainly in the property which allows the two detergents to be mixed in various proportions so that the surface charge which the micelle carries can be readily varied from fully positive to fully negative while at the same time maintaining the other components, electrolyte and water, in constant proportion to the total detergent. Only decanol content varies significantly throughout the range of mesophases. The quadrupole splitting from a quadrupolar nucleus is determined by the quadrupole coupling constant, Q, and the degree of alignment, S, of the electric field gradients with which the quadrupole moment interacts. The splitting, Av,is then given by eq 1 where it is assumed that the asymmetry in the electric field
Av =
3Qs 2 I ( 2 I - 1)
gradient is negligibly small. For ions of tetrahedral or higher symmetry the splitting is zero unless the ion is distorted from its high symmetry. Distortion can be caused by binding interactions3 or by polarization of the ion.I0 Should more than one type of interaction occur such as having free and bound ions in equilibrium (10) Bailey, D.; Buckingham, A. D.; Fujiwara, F.; Reeves, L. W. J . Map. Reson. 1915, 18, 344-357.
0 1985 American Chemical Society
2658
The Journal of Physical Chemistry, Vol. 89, No.12, 1985
then, provided exchange is fast, an averaged quadrupole splitting will be obtained. The splitting will then be determined by quadrupole splittings, Au,, characteristic of each species present and the proportion, Xi, of that species so that eq 2 is obtained.
Au = ZAu,Xi i
Studies of the interactions of alkali-metal and halide ions in the mixed amphiphile system of dodecanoate/alkyltrimethylammonium have proven to be very s u c ~ e s s f u l .In ~ ~this ~ system the micellar charge can be varied as required so that binding sites of counterions can be created or eliminated in a systematic manner. Furthermore, the mesophases employed are nematic phases which are aligned by the magnetic induction of the nuclear magnetic resonance (NMR) spectrometer utilized to monitor the quadrupole splittings. The alignment of the liquid crystalline materials leads to highly resolved NMR spectra which allows ready detection of signals. In this study nitrogen- 14 quadrupole splittings were used to investigate the interactions of the ammonium and tetramethylammonium ions with the dodecanoate amphiphile. Similarly, chlorine-35 and boron-1 1 quadrupole splittings were utilized in the investigation of perchlorate and tetrafluoroborate binding to the trimethylammonium amphiphile. These ions with the exception of tetrafluoroborate were also investigated in the optically active potassium N-hexadecanoyl-I-prolinate/tetradecyltrimethylammonium bromide system. The model of ion binding adopted in this study, which has been discussed in detai1,7*8.11J2 is a three-site model. The various sites have the following characteristics: site I, the ion is held within the micellar surface by binding interactions with two or more amphiphile head groups; site 11, the ion is undergoing binding interactions to one amphiphile and is assumed not to be located in the plane of the bilayer but rotated out of the plane because of interactions with the similarly charged amphiphile introduced to disrupt binding; site 111, the ion is essentially free and located in the interstitial water occupying the volume between micelles. In principle, site I1 could correspond to a composite of, or either one of, two sites, one site a specific binding site and the other a diffuse binding site where the ion is bound in a potential but not to a specific location. The model assumes that site I is occupied preferentially over sites I1 and I11 and site I1 is occupied at the expense of site 111. Under these conditions an equation relating the observed quadrupole splitting to the mole fraction of binding amphiphile can readily be written as eq7
+
AU = [AuICD(~X - (n - 1)) AvIICD(n - 1) X (1 - x ) + A u I I I c E I / [ x c D + CEl (3a) 1 1 x 1 ( 1 - l/n)
Radley and Tracey in a linear fashion as charge develops. Thus, two corrections to eq 3 can reasonably be made: (i) linear displacement of ions from site I to I1 as charge development weakens binding in site I and (ii) linear displacement of ions into site 111 from both sites I and 11. A more sophisticated treatment is probably not warranted. Incorporation of these two modifications into eq 3 provides AU = [A(AuIEC + AVII((1 - B)C D)) AuIII(xCD(~A ) + CE)] / [ X C D + CEl (4a)
+
+
1 2 x I ( 1 - l/n) AU = [AAUIIXCD + Av~I~(xCD( 1 - A ) f CE)]/ [XCD + c ~ ] (4b)
(1 - l / n ) Ix 1 0 In this equation A = ko - kl( 1 - xCD) and E = k2 - k3n(1 - x) while the other parameters are as defined for eq 3. The parameter A provides a crude method for probing the effect of charge development on the efficiency of binding. A value of ko = 1 means all binding sites are occupied in the pure detergent, Le., x = 1. kl is sensitive to the development of charge on the micellar surface; that is, as x ranges from 1 to 0,a charge of the same sign as that of the ion being considered develops on the micelle surface. This influences binding efficiency which is reflected by the deviation of kl from zero. A value of kl greater than ko means that the binding ions will be completely displaced into the interstitial water, site 111, before the micelle develops its maximum charge. In this regard, the value of ko in many respects is simply a scale factor; halving ko approximately doubles AuI and AvII but has a minimal effect on the calculated curve. This means that the nature of the binding can be probed without knowing the extent of binding. Within the limits of the approximation leading to eq 4, kl provides the only measure of the strength of ion binding relative to a free ion (site 111). kl will be dependent on the effects of ion competition for binding sites if more than one type of ion is present. Information concerning the relative strengths of ion binding in either site I or site I1 is provided by the factor E . In E, a k2 of 1 implies that at x = 1 no site I1 binding occurs, except probably as a transient phenomenon when ions exchange between sites I and 111. k3 like kl is sensitive to charge development on the micelle. It is dependent on the destabilization of site I relative to site I1 as amphiphiles carrying the same charge as the ion bound in the interface occupy a progressively higher proportion of that interface. Ions bound tightly in site I will be characterized by a k3 near zero while those that freely move into site I1 will have a k3 in the order of k2. It should be noted that eq 4 makes no effort to address the problem of ions which are very tightly bound in site I. Experimental Section
(1 - l / n ) 1 x 1 0 where n is the number of binding amphiphiles in site I and x is the mole fraction of that amphiphile in total detergent. C, represents the electrolyte concentration relative to a detergent concentration, CD, of 1. It has been found that for the alkali-metal and halide ions somewhat better agreement between calculated and observed splittings is obtained if some provision is made for the change in surface charge of the micelle.8 When binding is quite weak as might reasonably be expected for a tetrahedral ion such as tetramethylammonium, displacement from site I to site I1 may occur more quickly than provided for in eq 3 and, furthermore, a concurrent general displacement into site 111 may also occur. It is possible to account for these effects in a rudimentary fashion by assuming that displacement occurs (1 I ) Hecker, L.; Reeves, L. W.; Tracey, A. S.Mol. Cryst. Liq. Cryst. 1979, 53, 77-87. (12) Lee, Y.; Reeves, L. W.; Tracey, A. S. Can. J . Chem. 1980, 58, 110-123.
The potassium dodecanoate/alkyltrimethylammoniumbromide liquid crystalline system utilized in this study has been previously described,11J2 and the procedure utilized here differs little from that description. The major difference is that tetradecyltrimethylammonium bromide instead of hexadecyltrimethylammonium bromide was utilized for mesophase formation. Complications generally are encountered when one prepares mixed amphiphilic systems. The major problem is mesophase stability which, to a large extent, can be overcome through adjustments of decanol content. The main criterion, that micelle alignment stay relatively constant, has been established for the potassium dodecanoate/decyltrimethylammonium bromide system.12 The close correspondence between deuterium quadrupole splittings from D20 in that system and this indicates no significant differences as expected since the head group of the amphiphile has not been changed. The potassium N-hexadecanoyl-2-prolinate/tetradecyltrimethylammonium bromide mesomorphic system has been described in detail e1~ewhere.l~It differs little is behavior from the (13) Tracey, A. S.; Radley, K. Mol. Cryst. Liq. Cryst. 1985, 122, 77-87.
The Journal of Physical Chemistry, Vol. 89, No. 12, 1985 2659
Tetrahedral Ions in Aqueous Surfactant Solution
TABLE I: Mesophase Compsitions and Parameters Measured for the Potassium Dodecanoate/Alkyltrimethylammonium Bromide Mixed Detergent Liquid Crystalline System
quadrupole splittings,' kHz X
TDTMABrb
0.00
336
0.10 0.20 0.30 0.35 0.375 0.40
47
270
71
236 182 105
88 168 154 140
0.55 0.60
126 112
0.65 0.70
0.90
24
303
0.45 0.50
0.80
composition, mg DTMABrb KDodecb
98 84 67
84 90 95 107 119 131 143 155 166 190 214
34
1.oo
238
AVD
DeOHb
D,Oe
(D,O)
55
s1 s2 s3 s1 s2 s3 s1 s2 s3 s1 s2 s3 s3 s3 s1 s2 s3 s3 s1 s2 s3 s3 s1 s2 s3
0.003 0.002 0.000 -0.008 -0.013 -0.014 -0.008 -0.012 -0.015 -0.010 -0.005 -0.016 -0.006 0.027 0.007 0.01 1 0.005 0.012 0.038 0.039 0.03 1 0.073 0.055 0.070 0.073 0.112 0.127 0.143 0.112 0.136 0.158 0.126 0.147 0.178 0.160 0.166 0.222 0.180
35 20 5 0 20 30
20 10 5 0 5 0 0 5 10 0 15 20 10 35 40 30 60 65 50
s3 s1 s2 s3 s1 s2 s3 s1 s2 s3 s1 s2 s3
AVB
(BF,-)
AVN
(NH,+)
AVN
AVCl
(N(CH,),+)
(Clod-)
0.048 2.59 0.538
0.156 0.040 3.15
0.592
0.029 0.035 3.76
0.638
-0.280 0.033 4.38
0.723 0.779 0.526
-0.542 -0.864 0.056 2.23
0.322 0.346
-1.39 -1.57 0.052 2.63
0.307 0.163
-1.73 -1.79 0.050 1.67
0.163 0.087
-1.79 -1.54 0.141 0.565
0.025
-1.015 0.205 0.0
0.010
0.954 0.322 -0.087
0.006
2.82 0.525 -0.213
0.016
4.51
Signs of quadrupole splittings are relative signs only. bAbbreviations: tetradecyltrimethylammonium bromide, TDTMABr; decyltrimethylammonium bromide, DTMABr; potassium dodecanoate, KDodec; decanol, DeOH. cEach sample contains 900 mg of a D20 solution of the following compositions. S1: D20, 20 g; CsC1, 1.0 g; tetramethylammonium chloride, 0.2 g. S2: D20, 20 g; NaBr, 0.5 g; KC104, 0.1 g. S3: D20, 24 g; NH4BF4, 0.3 g; CSC1, 1.8 g. TABLE II: Mesophase Compositions and Parameters Measured for the Potassium N-Hexadecanoyl-l-prolinate/Tetradecyltrimetbylammonium Bromide Liauid Crvstalline Svstem ~
X 0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70 0.80 0.90 1.oo
composition,' mg TDTMABf I-KHDP 336 303 270 236 202 168 134 101 67 34
38 77 115 154 192 23 1 269 308 346 384
DeOHc
AvD(D20)
40 35 30 25 17.5 15 15 17.5 27.5 37.5 50
0.002 0.020 0.044 0.061 0.08 1 0.109 0.151 0.157 0.215 0.243 0.218
quadrupole splittings; kHz Av,(Cl-) Ava(C104-) AvN(NH4+) 3.19 1.87 0.035 -1.08 -1.93 -2.57 -2.98 -2.48 -2.41 -1.85 -1.06
2.97 3.28 3.51 3.34 3.10 3.11 2.78 1.71 0.655 0.080 -0.230
0.161 -0.092 -0.360 -0.499 -0.584 -0.661 -0.628 -0.344 0.033 0.491 0.789
~~~~
AvN(N(CHI),+ 0.052 0.052 0.055 0.046 0.041 0.044 0.055 0.057 0.089 0.126 0.148
"Each sample contains 850 mg of a D20 solution of the following composition: D20, 20 g; CsCI, 0.4 g; LiBr, 0.1 g; NaCI, 0.1 g; KCI, 0.1 g; KC104, 0.2 g; NH,CI, 0.75 g; tetramethylammonium chloride, 0.5 g. Signs of quadrupole splittings are relative signs only. Abbreviations: tetradecyltrimethylammonium bromide, TDTMABr; potassium N-hexadecanoyl-I-prolinate, I-KHDP decanol, DeOH. above system. The mesophase compositions and various parameters measured are given in Tables I and 11. N-Hexadecanoyl-/-prolinewas prepared according to literature procedures for the formation of amides of amino acids.14 The (14) Jungermann, E.; Gerecht, J. F.;Krems, I. J. J . Am. Chem. Soc. 1956, 78, 172-174.
product was crystallized twice from petroleum ether (60-80 "C). Carbon- 13 magnetic resonance was employed to check that no hexadecanoic acid was present in the crystalline product. The product was taken up in ethanol and then made alkaline with KOH. The product was obtained from the ethanol by adding ethyl acetate, and then it was recrystallized from ethyl acetate/ethanol. Care was taken in the preparation of the salt so that excessively
2660 The Journal of Physical Chemistry, Vol. 89, No. 12, 1985
Radley and Tracey
I
A boo.
2004 -1.01
b >' 0L ._o-os,-."
O-,'
~
o.---
9 ",O
'?
a '-
b-ua..c
0
0
0.9
0.6
0.3
Mole Fraction K-Carboxylate
Figure 1. The measured 14Nquadrupole splittings are given as a function of the mole fraction potassium dodecanoate (A) and potassium N-hexadecanoyl-Z-prolinate (B) in total detergent. Superimposed on the ob-
served points are the calculated curves. strong basic conditions would not cause partial hydrolysis of the amide. I3CN M R was used to check for the presence of potassium hexadecanoate; if detected, the product was recycled to the free amide, and if not detected, the potassium N-hexadecanoyl-lprolinate was again recrystallized from ethyl acetate/ethanol to yield the final product. All N M R spectra were obtained at 303 K from samples in 5-mm sample tubes. To aid in decreasing equilibration times, samples were maintained in a warm water bath (303 K) until being placed in the N M R spectrometer. The spectrometer utilized in this study was a 400-MHz instrument equipped for multinuclear operation. Results and Discussion
The interactions of ammonium ion and its various methylated derivatives in the sodium decyl sulfate liquid crystalline system have previously been in~estigated.'~The results indicated that dimethylammonium interacted most strongly with decyl sulfate, the mono- and trimethylated derivatives less strongly, and the ammonium and tetramethylammonium ions least effectively as judged by the perturbing effect on the hydrocarbon chain motions of the decylsulfate. It was suggested that these last two ions did not penetrate efficiently into the hydrocarbon region of the bilayer, the tetramethylammonium because of its bulkiness and the ammonium ion because it was strongly hydrophilic. Since the three-site model of ion binding provides good agreement between calculated and observed curves for the alkali metal and halide ions, it should also be applicable to tetrahedral ions such as ammonium, tetramethylammonium, and perchlorate. The binding of these ions has been investigated in two mixed mesomorphic systems, the potassium dodecanoate/alkyltrimethylammonium bromide system and the potassium N-hexadecanoyl-l-prolinate/tetradecyltrimethylammoniumbromide system. Mesophases prepared from N-hexadecanoyl-I- or Nhexadecanoyl-d,l-prolinatehave not previously been reported. This system displays some unusual cholesteric behavior and is discussed in detail e1~ewhere.I~The potassium dodecanoate/alkyltrimethylammonium/decanol/water/electrolyteliquid crystalline system has been extensively in~estigated.~~*~'l~~* The corresponding prolinate materials behave similarly with the major difference being that rather large amounts of electrolyte are required. For the dodecanoate mesophase, the electrolyte to amphiphile ratio is typically 1:2 or 1:3, while for the prolinate mesophase the proportion is 2.8:l. It seems that such an increase in preparation (15) Reeves, L. W.; Tracey, A. S.J. Am. Chem. Soc. 1975,97,5729-5734.
u---a 1
J
0.3 0.9 0.6 Mole Fraction K-Carboxylate
Figure 2. The behavior of the I4N quadrupole splittings from tetramethylammonium as a function of the mole fraction of potassium dodecanoate (A) or potassium N-hexadecanoyl-l-prolinate(B) in total amphiphile is displayed are well as are the calculated curves.
of electrolyte has a substantial effect on the character of the binding of ions. Table I provides the results obtained for the various ions investigated in the potassium dodecanoate/alkyltrimethylammonium bromide system while Table I1 provides the corresponding results for prolinate. Figure 1 diagrammatically presents the results for the ammonium ion from the two systems. The relative magnitudes of the splittings from the two mesophases reflect the large difference in the proportion of electrolyte contained in the two materials. Beyond this there is a basic difference between the two curves. The curve for the dodecanoate system is best reproduced from eq 4 when n = 3 which indicates that the ammonium ion in site I binds simultaneously to three amphiphiles. In the prolinate case (Figure 1B) the curve is best fit with n = 2. The characteristic quadrupole splittings for the three sites are Avl = 6.74 and 2.72 kHz, AvII = -4.62 and -2.00 kHz, and AvIII = +0.25 and +0.17 kHz for the dodecanoate (Figure 1A) and prolinate (Figure 1B) curves, respectively. Signs of splittings are relative signs only. Figure 2 presents the results obtained for the tetramethylammonium ion. These curves are qualitatively different from those for the ammonium ion. The large quadrupole splitting decreases until the micellar surface charge is approximately neutral and then remains more or less constant with further development of positive charge. This situation is ambiguous since AvlI could be small giving the flat regions or the tetramethylammonium in this region may essentially all be in site 111 so that the quadrupole splitting is constant. Alternately, it may be that the ion occupies only two sites, one corresponding to the free ion, site 111, and the other a site I or site 11. Considering the nature of the tetramethylammonium ion, it seems reasonable that this ion is bound by a potential rather than to a specific site in the micellar surface. Such a situation can be reproduced from eq 4 putting n = 1. The two observed curves, Figure 2, A and B, are reproduced very well by such a calculation. However, Figure lA, corresponding to the dodecanoate system, is reproduced as well if not slightly better with n = 2 in a three-site description. The corresponding calculation for the prolinate system provides poor agreement between the calculated and observed curves when n = 2. Neither experimental curve is fit at all well when it is assumed that n = 3 for the calculations. If one accepts that the two-site model with n = 1 provides the best description of the interactions of tetramethylammonium ion, then A q I = 0.63 and 0.44 kHz and Avlll = 0.044 and 0.052 kHz, respectively, for the two systems. The binding is such that essentially all ions are in Site I11 by the time X has decreased to ~ 0 . from 6 1.0. The values of k l obtained for the two systems are 2.63 and 2.74 for the dodecanoate and pro-
J . Phys. Chem. 1985,89, 2661-2665 ,...... ,’O
0
0
D’- - - - ---n
0,’
N t I
* I CI-35 ClOl
A I
\
,
0.9
8
I
0.6
8
8
,
0.3
Mole Fraction K-Carboxylate
Figure 3. The 3sC1quadrupole splitting from the perchlorate ion is displayed as a function of alkyltrimethylammoniumin total detergent. The second component is potassium dodecanoate (A) and potassium N-hexadecanoyl-l-prolinate(B). The calculated curves are also dis-
played. linate mixed mesophases, respectively. The binding of perchlorate ion, C104-, and tetrafluoroborate, BF4-, was investigated to the dodecanoate systems and as well C104- in the prolinate system. In this case, ion binding is to the cationic component of the mesophase, decyl- and tetradecyltrimethylammonium bromide. Figure 3 shows the behavior of the quadrupole splittings as a function of the mole fraction of alkyltrimethylammonium in total detergent. The observed curves clearly are very different. On analysis of Figure 3A, it is clear that good agreement is obtained when it is assumed that C104is interacting with three trimethylammonium head groups when in site I. The characteristic quadrupole splittings for the perchlorate ion are AvI = 3.29 kHz, AvII = 10.9 kHz, and AqII = -0.21 kHz with a k , = 1.23 which implies that the buildup of negative charge on the bilayer surface is sufficient to force all C10, ions into the aqueous region of the mesophase (site 111) even though a small proportion of positively charged amphiphiles are still contained in the micelle.
2661
Analysis of the results displayed in Figure 3B is straightforward. Good agreement between calculated and observed curves is obtained when the number of liganding amphiphiles is assumed to be two. With this value for perchlorate ion in the prolinate system, the values for AvI, AvII, and AvIIIare 12.1, 34.9, and -0.23 kHz, respectively, with a k , of 0.71. There is a discrepancy in these results. Perchlorate is binding to trimethylammonium and not to carboxylate so that the number of liganding amphiphiles in site I should be independent of the anionic amphiphile employed in the study; that is to say, n should be the same in both studies. Investigation of the chloride ion reveals behavior similar to that observed for the perchlorate. In the potassium dodecanoate/ alkyltrimethylammonium bromide mesophase system, chloride was found to bind to three trimethylammonium head groups’ whereas in the prolinate system it is bound by two head groups. In the cases investigated here, ammonium, perchlorate, and chloride, similar behavior has been observed, in that the number of liganding amphiphiles is described from three to two. A similar result has been obtained from a study of alkali-metal ion binding.13 There is approximately a factor of 10 difference in the amount of electrolyte present in the two systems. It does seem that this has important consequences on the interface characteristics. It should be pointed out that the effect of electrolyte is not to cause a phase change from the lamellar disklike mesophase to a cylindrical system, thus giving rise to the change in binding. A study of these systems with a polarizing microscope showed both mesophases were of the fragmented lamellae type, N-. It is not clear at this time whether a phase transition to a second lamellar type mesophase has occurred. Boron tetrafluoride was investigated only in the potassium dodecanoate/alkyltrimethylammonium system. Like the other tetrahedral ions with the exception of tetramethylammonium, the number of liganding amphiphiles in site I is three. The characteristic quadrupole splittings obtained for the three binding sites are AvI = 0.83 kHz, AvlI = 2.67 kHz, and AvIII = -0.016 kHz, respectively.
Acknowledgment. Thanks are gratefully extended to the Natural Sciences and Engineering Research Council of Canada for its financial support of this work. Registry No. NH4+,14798-03-9;Me4N+,51-92-3; CIO;, 14797-73-0; 14874-70-5; potassium dodecanoate, 10124-65-9;potassium Nhexadecanoyl-I-prolinate,956 16-89-0;decyltrimethylammonium bromide, 2082-84-0; tetradecyltrimethylammonium bromide, 1 1 19-97-7;decyl alcohol, 1 12-30-1.
BF,,
Thermodynamlc Propertles of the Charge-Asymmetric Electrolyte Mixture In(C104),-HCI0,-H20 J. Vanhees, J. P. Franqois, J. Mullens, J. Yperman, and L. C. Van Poucke* Limburgs Universitair Centrum, Departement SBM, Universitaire Campus, B- 361 0 Diepenbeek, Belgium (Received: October 18, 1984; In Final Form: January 31, 1985) The activity coefficients of indium perchlorate in aqueous indium perchlorate-HC104 solutions have been determined at 25.0 OC. The higher order limiting law of Friedman for the free energy interaction parameter gowas tested with total and partial molal excess functions. Experimental go values were compared with theoretical values calculated according to the primitive model for electrolyte solutions. From Friedman’s theory a suitable extrapolation function was obtained which allows for the determination of the standard reduction potential of the In3+;Inelectrode. Introduction Modern theories of electrolyte solutions, based on statistical mechanics, try to avoid the rather artificial aspects of the Debye-Huckel theory and the different adaptations required to improve that theory for other than extremely dilute solutions. 0022-3654/85/2089-2661$01 S O / O
FriedmanI4 has developed a theory for electrolyte mixtures based on Mayers cluster expansion.’ From this treatment result higher (1) Friedman, H. L. “Ionic Solution Theory”; Interscience: New York,
1962.
0 1985 American Chemical Society
