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liquid interfaces in the presence of added salt and their role in emulsion stability
NOTES Adsorption Studies of Sodium Deoxycholate at Various Liquid/Liquid Interfaces in the Presence of Added Salt and Their Role in Emulsion Stability Adsorption studies of sodium deoxycholate at various liquid/liquid interfaces in the presence of different amounts of NaCI have been carried out by measuring interfacial tension at 20°C using an Agla micrometer syringe. The stability of these systems has been assessed by estimating the surface charge and surface potential. An attempt has also been made to evaluate the number of molecules affsorbed, surface excess, and the area of the adsorbed molecules. The pressure-area (Tr-A) curves have been drawn using the above data.
Introduction
which can deliver liquid accurately up to _+0.0002 ml. The nonaqueous phase was in a tall tube and the aqueous phase containing different amounts of sodium chloride and sodium deoxycholate was in the syringe. The average age of the drop was 3.5 sec. The reproducibility of the experimental data was 5%. Theoretical. The interfacial tensions were calculated with the known densities of the respective phases, volume of the drop, and radius of the tip of the syringe using the relation
The bile salts occupy an important role in emulsion studies due to their immense importance in cell membranes. The role of bile salts in the intestinal adsorption of triglycerides and cholesterol has been reviewed by Kelvin (l). Recently, Trillo and co-workers (2) studied the monolayers of mixed films of cholesterol and lecithin with bile acids. Haydon (3) reviewed the properties of lipid bilayers at a w a t e r - w a t e r interface. The studies on the mixed micelle formation in aqueous solutions of alkyl trimethylammonium cholates have been reported by Barry and Gray (4, 5). Sastry and Srivastava (6-8) studied the role of some biological materials in emulsion stability in the presence of electrolytes, surface active agents, and dyes. Monolayer studies on a variety of phospholipids have been reported and included the discussion of cholesterol interaction (9). Shah and Schulman (10) studied the effect of the binding of metal ions to monolayers of various phospholipids. A review on the more practical uses of lecithins has been given (11). Therefore, the present paper deals with the adsorption of sodium deoxycholate at various liquid/liquid interfaces and their role in emulsion stability Of the oilwater systems.
Yo-w = V(dw - do)gF/r,
[1]
where dw and do are the densities of the aqueous and nonaqueous phases, respectively, r is the radius of the tip of the syringe, g is the gravity, V is the volume of the drop, and F is the factor depending upon the value of V/r 3, taken from the standard Table (12). The surface pressures were calculated by the usual equation. The surface potential of an oil-water emulsion can be estimated theoretically with the known surface charge. The charge on the Stern layer is given by the Langmuir-Stern equation (13) ( 0-1 = evN1 1 +
Experimental
0"6X1024 ) 18n-~xp~ev-~o/kT) .
[23
The charge on the diffuse Gouy layer is given by the relation
(a) M a t e r i a l s . Sodium deoxycholate of a high degree of purity (i.e., even 99%) was supplied from Difco. The benzene, toluene, xylene, petroleumether, and sodium chloride used were of BDH, Analar grade. Doubly distilled water was used throughout the measurements. All glass apparatuses were cleaned and steamed before use. (b) P r o c e d u r e . The interfacial tensions were measured by the drop volume method at 20°C using an "Agla" micrometer syringe (Burroughs Wellcome)
All the symbols have the usual meanings. Taking into account the condition of electrical neutrality for the entire double layer, o'1 + 0"2 = 0-.
[4]
A standard graph has been plotted between the 179 0021-9797/78/0641-0179502.00/0
Journal of Colloid and Interface Science, Vol. 64, No. 1, March 15, 1978
Copyright © 1978 by Academic Press, Inc. All rights of reproduction in any form reserved.
180
NOTES TABLE I
Values o f Interfacial T en sion, Surface Pressure, N u m b e r of Mol e c ul e s A d s o r b e d pe r Square C e nt i me t e r, A r e a of the Molecules, Surface E x c e s s , and e@o/kT in t he P r e s e n c e of 0.1 M NaCI Concentration of sodium deoxycholate (moles/liter)
Surface pressure (zQ (dyrgcm)
No. of moles adsorbed/cm~ (n x I0is)
Area (A) (~,)
Surface excess I"s × 1011)
eqJolkT
19.39 18.26 16.86 16.07 12.92 10.22 8.39 7.17 6.61
0.89 2.02 3.42 4.21 7.36 10.06 11.89 13.11 13.67
0.36 2.99 4.06 4.67 5.66 5.77 5.85 5.89 5.94
2778.0 334.4 245,7 214.1 176.7 173.3 170.9 169.8 168.4
0.59 4.96 6.72 7.76 9.40 9.58 9.71 9.78 9.86
0.1168 1.6150 1.9460 2.1210 2.3940 2.4130 2.4210 2.4330 2.4410
23.43 23.05 22.02 19.24 17.16 16.89 14.64 11.47 10.08 8.72
5.87 6.25 7.28 10.06 12.14 12.41 14.66 17.83 19.22 20.58
2.40 2.52 5.47 7.15 7.70 8.04 8.23 8.31 8.40 8.47
416.6 396.8 182.8 139.8 129.8 124.3 121.4 120.3 119.0 118.0
3.95 4.17 9.08 11.87 12.75 13.35 13.67 13.80 13.95 14.07
1.3800 1.4610 2.3301 2.7050 2.8410 2.9001 2.9190 2.9270 2.9390 2.9580
27.20 25.42 23.53 20.16 17.80 15.50 11.62 9.87 9.42
3.64 5.42 7.31 10.68 13.04 15.34 19.22 20.97 21.42
1.58 1.67 6.57 6.89 9.37 9.58 10.02 10.11 .
2.62 2.77 10.91 11.44 15.56 15.91 16.64 16.79
0.9537 0.9924 2.5880 2.6460 3.1140 3.1530 3.2300 3.2580
.
632.9 598.8 152.2 145.1 106.7 104.4 99.9 98.9 .
29,11 27,70 25,84 23.46 19.85 17.44 17.14 14.73 11.32 9.70 9.37
2.85 4.26 6.12 8.50 12.11 14.52 14.82 17.23 20.64 22.26 22.59
1.30 1.44 4.36 6.77 8.47 10.02 10.08 10.21 10.26 10.32 .
2.15 2.37 7.24 11.24 14.06 16.64 16.74 16.96 17.04 17.14
0.7980 0.8630 2.0240 2.6270 2.9390 3.2300 3.2380 3.2500 3.2700 3.2900
.
970.9 694.4 229.4 147.7 118.1 99.9 99.8 98.0 97.9 97.0 .
Interracial tension (3') (dyrgcm)
Petroleum-ether/water system 1.0 5.0 1.0 2.0 5.0 2.0 5.0 8.0 1.0
x x x x x x x × ×
10 .6 10 .6 10 .5 10 -5 10 -~ 10 -4 10.4 10.4 10 .5
M M M M M M M M M
Benzene/water system 1.0 1.0 2.0 5.0 8.0 1.0 2.0 5.0 8.0 1.0
x x x x x x x x x x
10.6 10 .5 10 .5 10-~ 10.5 10-4 10 -4 10 -4 10 -4 10 -4
M M M M M M M M M M
Toluene/water system 5.0 1.0 2.0 5.0 1.0 2.0 5.0 8.0 1,0
x × x x x x x x x
10 -6 10 -5 10 -5 10 -5 10-4 10 -4 10 .4 10-4 10-5
M M M M M M M M M
.
Xylene/water system 1.0 × 10-6 M
5.0 x 1.0 x 2.0 × 5.0 x 8.0 x 1.0× 2.0 x 5.0 x 8.0 x 1.0 x
10-6 10 -5 10 -s 10 -5 10-5 10 -4 10 -4 10-4 10 -4 10 -5
M M M M M M M M M M
Journal of Colloid and Interface Science, Vol. 64, No. 1, March 15, 1978
.
NOTES
181
T A B L E II Values of Interfacial Tension, Surface Pressure, N u m b e r of Mol e c ul e s A d s o r b e d p e r Square C e n t i m e t e r , A r e a of the Molecules, Surface E x c e s s , and e ~ o / k T in the P r e s e n c e of 1.00 M NaC1 Concentration of sodium deoxycholate (moles/liter)
Surface pressure (~r) (dyrdcm)
No. of moles adsorbed/cm~ (n x 10TM)
Area (A) (/~,)
Surface excess F~ x 10~)
etOo/kT
18.63 16.63 14.40 12.64 11.50 9.97 7.09
1.65 3.65 5.88 7.64 8.78 10.31 13.19
0.52 3.01 4.07 6.01 6.32 6.45 6.56
1923.0 332.2 245.7 166.4 158.2 155.0 152.4
0.86 5.00 6.76 9.99 10.49 10.71 10.89
0.0500 0.3250 0.4500 0.6750 0.7000 0.7250 0.7500
22.68 20.5• 15.59 11.72 10.66 9.56 7.36 4.70 3.24 2.38
6.62 8.79 13.71 17.58 18.64 19.74 21.94 24.60 26.06 .
2.78 2.81 5.58 8.06 8.40 8.48 8.56 8.68 8.73
359.7 355.9 179.2 124.1 119.0 117.9 116.8 115.2 114.5 .
4.61 4.66 9.26 13.39 13.95 14.08 14.21 14.41 14.49
0.3000 0.3250 0.6250 0.9250 0.9500 0.9600 0.9750 0.9900 1.0000
23.43 22.29 17.02 13.42 11.77 10.17 7.74 4.98 3.58 2.68
7.41 8.55 13.82 17.42 19.07 20.67 23.10 25.86 27.26 28.16
2.43 2.58 7.14 8.32 9.37 9.42 9.86 9.95 . .
4.03 4.29 11.86 13.82 15.56 15.80 16.37 16.52
0.2500 0.2750 0.8000 0.9500 1.0500 1.0750 1.1200 1.1250
24.51 23.83 17.51 13.14 11.27 11.10 8.07 4.84 3.72 2.56
7.45 8.13 14.45 18.82 20.69 20.86 23.89 27.12 28.24 29.40
2.25 2.40 8.00 9.21 9.64 10.06 10.25 10.37 . .
3.73 3.98 13.28 15.29 16.00 16.71 17.02 17.22
0.2500 0.2700 0.9000 1.0500 1.1000 1.1500 1.1700 1.2000
]nteffacial tension (30 (dyn/cm)
Petroleum-ether/water system 1.0 5.0 2.0 5.0 8.0 2.0 8.0
x x x x x x x
10 -6 10-6 10 -5 10-5 10 -5 10 -4 10-4
M M M M M M M
Benzene/water system 1.0 5.0 2.0 5.0 8.0 1.0 2.0 5.0 8.0 1.0
x x x x x x × x x ×
10 -5 10-5 10 -5 10 -5 10-5 10-4 10 -4 10 -4 10-4 10 -3
M M M M M M M M M M
.
.
.
Toluene/water system 1.0 5.0 2.0 5.0 8.0 1.0 2.0 5.0 8.0 1.0
x x x x x x x x x x
10-n 10-5 10-5 10 -5 10-5 10-4 10 -4 10 -4 10-4 10-8
M M M M M M M M M M
. .
411.5 387.6 140.3 120.2 106.7 106.2 101.4 100.5 . .
. .
444.4 416.7 125.0 108.6 103.7 99.8 97.9 97.8 . .
. .
Xylene/water system 1.0 5.0 2.0 5.0 8.0 1.0 2.0 5.0 8.0 1.0
x x x x x x x x x x
10 -5 M 10 -6 M 10 5 M 10 -2 M 10 -5 M 10 4 M 10-4 M 10 -4 M 10-4 M 10-3 M
. .
Journal of Colloid and Interface Science, Vol. 64, No. 1, March 15, 1978
182
NOTES
ol a.
:4
d
-4
d
3
4
-6
LOG.
-~
-4.
-3
CONC
Fro. 1. Curves showing the variation in interracial tension with concentrations of sodium deoxycholate in presence of (a) Q 0.1 M NaC1, • 1.0 M NaCI for benzene; & 0.1 M NaC1, [] 1.0 M NaC1 for toluene/water system. (b) E) 0 . 1 M NaCI, • 1.0M NaC1 for Xylene; A 0 . 1 M NaCI, [] 1.0 M NaCI for petroleum-ether system.
IV
b
A R E A - A~
o
:~o 200
460
~o
I00
eoo
FIG. 2. Curves showing the variation of surface pressure (rr) with Area (A) in presence of 0.1 M NaC1 for × pet.-ether, [] benzene, Q toluene, and A xylene systems. Journal of Colloid and Interface Science, Vol. 64, No. 1, March 15, 1978
2OO
300
4O0
AREA A2
FtG. 3. Curves showing the variation of surface pressure (zr) with Area (A) in presence of 1.0 M NaC1 for × pet.-ether, [] benzene, (3 toluene, and A xylene systems.
NOTES
0
4-0
~,0
120~
FIG. 4. Curves showing the distribution of charge in different layers with surface potential tOo. I, (os/ev) × 10-13; II, (~rJev) x 10-13; III, (tr/ev) x 10-13, inpresence of 0.1 M NaC1; IV, (~rl/ev) x 10-13; V, (trJev) x 10-I3; and VI, (tr/ev) x 10 13 in presence of 1.0 M NaC1.
183
with increasing concentrations of sodium deoxycholate. Initially the decrease was less at lower concentrations of sodium deoxycholate and greater on increasing concentrations. The decrease in interfacial tension was greater in the case of 1.00 M NaCI than in the case of 0.10 M NaC1. The surface pressures (It) have been evaluated by subtracting various values of interfacial tension from the values of interfacial tension for clean interfaces. The curves between surface pressure and area 0 r - A ) have been plotted in Figs. 2 and 3. The decrease in area was sharp at low surface pressure due to the study crowding of sodium deoxycholate molecules. Moreover, the molecules have been closely packed in the region in which a large change in surface pressure was observed. The values o f surface excess (F~) and number of molecules adsorbed per square centimeter have also been calculated with the help of interfacial tensionlog molar concentration curves. The relevant data are recorded in Tables I and II. It is evident from these above tables that initially the increase in surface excess (F~) was sharp with the increase in concentration of sodium deoxycholate. The values of surface excess are almost constant for all systems from concentration 5.0 x 10.5 to 1.0 x 10-3 M. The experimental values of surface potential (tOo) corresponding to the amount of the adsorbed molecules, determined experimentally, were noted with the help of the theoretical curves (Fig. 4). It
amount of adsorbent (o/e) and surface potential (tOo) for uni-univalent electrolytes in Fig. 4. The amount of adsorbent (o/e) can also be evaluated experimentally with the help of interracial tension using the following relations:
Fs
=
-(l/RT)(dy/d In C)
[5]
[I
I
and
~r = evFs.
[6]
=9 x
With the help of the theoretical curve between (o/e) and too, the values of tOo satisfying the experimentally determined value of (o/e) are noted and recorded in Tables I & II.
Results
and Discussion
The interracial tension at varying concentrations of sodium deoxycholate and sodium chloride have been evaluated for petroleum-ether/water, benzene/water, toluene/water, and xylene/water systems at 20°C and plotted in Fig. 1. The values of interfacial tensions for clean interfaces were found to be 20.28, 29.30, 30.84, and 31.96 dyn/cm for petroleum-ether/water, benzene/water, toluene/water, and xylene/water systems, respectively. It is evident from Fig. 1 that a regular decrease in in~erfacia! tension was observed
o
20
60
40
80
-~ffo-
FIG. 5. Curves showing the variation of surface excess Fs x 1011 with surface potential tOo in presence of I, 0.1 M NaC1 and II, 1.0 M NaC1 for [] petroleumether, C) benzene, x toluene, and Sx xylene/water systems. Journal of Colloid and Interface Science,
Vol. 64, N o . l, M a r c h 15, 1978
184
NOTES
is evident that the surface potential increases as the concentration of sodium deoxycholate increases which shows the increase in the stability of the systems. The increase in surface potential at lower concentration of sodium deoxycholate is greater than that of higher concentration. Therefore, a slight increase in the stability of systems was found at higher concentrations of emulsifier. The values of surface potential (~0) have been found to be higher in the presence of 0.1 M NaCI than in the presence of 1.0 M NaCI for the same concentration of sodium deoxycholate. These low values of surface potential in the case of 1.0M NaC1 are due to the presence of an excess amount of NaC1 which was responsible for the reduction of surface potential of the system. The values of the surface excess (Fs) were plotted against the surface potential in Fig. 5. It is obvious that all the points fall on the same curve for all the liquid/liquid systems, which indicates that the surface potentials were independent of the nature of the nonaqueous phase molecules. ACKNOWLEDGMENTS
4. Barry, B. W., and Gray, G. M. T., J. Colloid Interface Sci. 52, 314 (1975). 5. Barry, B. W., and Gray, G. M. T., J. Colloid Interface Sci. 52, 327 (1975). 6. Sastry, T. G., and Srivastava, S. N., Bull. Chem. Soc. Japan 42, 291 (1968). 7. Sastry, T. G., and Srivastava, S. N.,Ind. J. Chem. 6, 728 (1968). 8. Sastry, T. G., and Srivastava, S. N., J. Colloid Interface Sci. 33, 468 (1970). 9. Van deenen et al., J. Pharm. Pharmacol. 14, 429 (1962). 10. Shah, D. J., and Schulman, J. H., J. Lipid Res. 6, 341 (1965). 11. Ghatak, S., and Krishnamurty, C. R., J. Sci. Ind. Res. 14A, 285 (1955). 12. "International Critical Tables," Vol. IV, pp. 435, McGraw-Hill New York, 1929. 13. Stern, 0., Z. Electrochem. 30, 508 (1924). 14. Vold, R. D., J. Colloid Sci. 16, 1 (1961). 15. Derjaguin, B., and Kussakov, M., Acta Phys. Chem. URSS 10, 75, 153 (1939). 16. Schenkel, J. N., and Kitchener, J. A., Trans. Faraday Soc. 56, 161 (1960).
The authors are very grateful to the authorities of U. G. C., New Delhi, for granting financial assistance.
M. K. SHARMA
MEERA SHARMA S. P. JAIN S. N. SRIVASTAVA
REFERENCES 1. Kelvin, H., Leech (Johennesb.) 36, 108 (1966). 2. Trillo, J. M., Fernandez, S. G., and Pedrero, P. S., J. Colloid Interface Sci. 26, 518 (1968). 3. Haydon, D. A., J. Amer. Oil Chem. Soc. 45, 230 (1968).
Journal of Colloid and Interface Science, Vol. 64, No. 1, March 15, 1978
Chemical Laboratories Agra College Agra 282002, India Received December 1, 1976; accepted August 13, 1977
Introduction
which can deliver liquid accurately up to _+0.0002 ml. The nonaqueous phase was in a tall tube and the aqueous phase containing different amounts of sodium chloride and sodium deoxycholate was in the syringe. The average age of the drop was 3.5 sec. The reproducibility of the experimental data was 5%. Theoretical. The interfacial tensions were calculated with the known densities of the respective phases, volume of the drop, and radius of the tip of the syringe using the relation
The bile salts occupy an important role in emulsion studies due to their immense importance in cell membranes. The role of bile salts in the intestinal adsorption of triglycerides and cholesterol has been reviewed by Kelvin (l). Recently, Trillo and co-workers (2) studied the monolayers of mixed films of cholesterol and lecithin with bile acids. Haydon (3) reviewed the properties of lipid bilayers at a w a t e r - w a t e r interface. The studies on the mixed micelle formation in aqueous solutions of alkyl trimethylammonium cholates have been reported by Barry and Gray (4, 5). Sastry and Srivastava (6-8) studied the role of some biological materials in emulsion stability in the presence of electrolytes, surface active agents, and dyes. Monolayer studies on a variety of phospholipids have been reported and included the discussion of cholesterol interaction (9). Shah and Schulman (10) studied the effect of the binding of metal ions to monolayers of various phospholipids. A review on the more practical uses of lecithins has been given (11). Therefore, the present paper deals with the adsorption of sodium deoxycholate at various liquid/liquid interfaces and their role in emulsion stability Of the oilwater systems.
Yo-w = V(dw - do)gF/r,
[1]
where dw and do are the densities of the aqueous and nonaqueous phases, respectively, r is the radius of the tip of the syringe, g is the gravity, V is the volume of the drop, and F is the factor depending upon the value of V/r 3, taken from the standard Table (12). The surface pressures were calculated by the usual equation. The surface potential of an oil-water emulsion can be estimated theoretically with the known surface charge. The charge on the Stern layer is given by the Langmuir-Stern equation (13) ( 0-1 = evN1 1 +
Experimental
0"6X1024 ) 18n-~xp~ev-~o/kT) .
[23
The charge on the diffuse Gouy layer is given by the relation
(a) M a t e r i a l s . Sodium deoxycholate of a high degree of purity (i.e., even 99%) was supplied from Difco. The benzene, toluene, xylene, petroleumether, and sodium chloride used were of BDH, Analar grade. Doubly distilled water was used throughout the measurements. All glass apparatuses were cleaned and steamed before use. (b) P r o c e d u r e . The interfacial tensions were measured by the drop volume method at 20°C using an "Agla" micrometer syringe (Burroughs Wellcome)
All the symbols have the usual meanings. Taking into account the condition of electrical neutrality for the entire double layer, o'1 + 0"2 = 0-.
[4]
A standard graph has been plotted between the 179 0021-9797/78/0641-0179502.00/0
Journal of Colloid and Interface Science, Vol. 64, No. 1, March 15, 1978
Copyright © 1978 by Academic Press, Inc. All rights of reproduction in any form reserved.
180
NOTES TABLE I
Values o f Interfacial T en sion, Surface Pressure, N u m b e r of Mol e c ul e s A d s o r b e d pe r Square C e nt i me t e r, A r e a of the Molecules, Surface E x c e s s , and e@o/kT in t he P r e s e n c e of 0.1 M NaCI Concentration of sodium deoxycholate (moles/liter)
Surface pressure (zQ (dyrgcm)
No. of moles adsorbed/cm~ (n x I0is)
Area (A) (~,)
Surface excess I"s × 1011)
eqJolkT
19.39 18.26 16.86 16.07 12.92 10.22 8.39 7.17 6.61
0.89 2.02 3.42 4.21 7.36 10.06 11.89 13.11 13.67
0.36 2.99 4.06 4.67 5.66 5.77 5.85 5.89 5.94
2778.0 334.4 245,7 214.1 176.7 173.3 170.9 169.8 168.4
0.59 4.96 6.72 7.76 9.40 9.58 9.71 9.78 9.86
0.1168 1.6150 1.9460 2.1210 2.3940 2.4130 2.4210 2.4330 2.4410
23.43 23.05 22.02 19.24 17.16 16.89 14.64 11.47 10.08 8.72
5.87 6.25 7.28 10.06 12.14 12.41 14.66 17.83 19.22 20.58
2.40 2.52 5.47 7.15 7.70 8.04 8.23 8.31 8.40 8.47
416.6 396.8 182.8 139.8 129.8 124.3 121.4 120.3 119.0 118.0
3.95 4.17 9.08 11.87 12.75 13.35 13.67 13.80 13.95 14.07
1.3800 1.4610 2.3301 2.7050 2.8410 2.9001 2.9190 2.9270 2.9390 2.9580
27.20 25.42 23.53 20.16 17.80 15.50 11.62 9.87 9.42
3.64 5.42 7.31 10.68 13.04 15.34 19.22 20.97 21.42
1.58 1.67 6.57 6.89 9.37 9.58 10.02 10.11 .
2.62 2.77 10.91 11.44 15.56 15.91 16.64 16.79
0.9537 0.9924 2.5880 2.6460 3.1140 3.1530 3.2300 3.2580
.
632.9 598.8 152.2 145.1 106.7 104.4 99.9 98.9 .
29,11 27,70 25,84 23.46 19.85 17.44 17.14 14.73 11.32 9.70 9.37
2.85 4.26 6.12 8.50 12.11 14.52 14.82 17.23 20.64 22.26 22.59
1.30 1.44 4.36 6.77 8.47 10.02 10.08 10.21 10.26 10.32 .
2.15 2.37 7.24 11.24 14.06 16.64 16.74 16.96 17.04 17.14
0.7980 0.8630 2.0240 2.6270 2.9390 3.2300 3.2380 3.2500 3.2700 3.2900
.
970.9 694.4 229.4 147.7 118.1 99.9 99.8 98.0 97.9 97.0 .
Interracial tension (3') (dyrgcm)
Petroleum-ether/water system 1.0 5.0 1.0 2.0 5.0 2.0 5.0 8.0 1.0
x x x x x x x × ×
10 .6 10 .6 10 .5 10 -5 10 -~ 10 -4 10.4 10.4 10 .5
M M M M M M M M M
Benzene/water system 1.0 1.0 2.0 5.0 8.0 1.0 2.0 5.0 8.0 1.0
x x x x x x x x x x
10.6 10 .5 10 .5 10-~ 10.5 10-4 10 -4 10 -4 10 -4 10 -4
M M M M M M M M M M
Toluene/water system 5.0 1.0 2.0 5.0 1.0 2.0 5.0 8.0 1,0
x × x x x x x x x
10 -6 10 -5 10 -5 10 -5 10-4 10 -4 10 .4 10-4 10-5
M M M M M M M M M
.
Xylene/water system 1.0 × 10-6 M
5.0 x 1.0 x 2.0 × 5.0 x 8.0 x 1.0× 2.0 x 5.0 x 8.0 x 1.0 x
10-6 10 -5 10 -s 10 -5 10-5 10 -4 10 -4 10-4 10 -4 10 -5
M M M M M M M M M M
Journal of Colloid and Interface Science, Vol. 64, No. 1, March 15, 1978
.
NOTES
181
T A B L E II Values of Interfacial Tension, Surface Pressure, N u m b e r of Mol e c ul e s A d s o r b e d p e r Square C e n t i m e t e r , A r e a of the Molecules, Surface E x c e s s , and e ~ o / k T in the P r e s e n c e of 1.00 M NaC1 Concentration of sodium deoxycholate (moles/liter)
Surface pressure (~r) (dyrdcm)
No. of moles adsorbed/cm~ (n x 10TM)
Area (A) (/~,)
Surface excess F~ x 10~)
etOo/kT
18.63 16.63 14.40 12.64 11.50 9.97 7.09
1.65 3.65 5.88 7.64 8.78 10.31 13.19
0.52 3.01 4.07 6.01 6.32 6.45 6.56
1923.0 332.2 245.7 166.4 158.2 155.0 152.4
0.86 5.00 6.76 9.99 10.49 10.71 10.89
0.0500 0.3250 0.4500 0.6750 0.7000 0.7250 0.7500
22.68 20.5• 15.59 11.72 10.66 9.56 7.36 4.70 3.24 2.38
6.62 8.79 13.71 17.58 18.64 19.74 21.94 24.60 26.06 .
2.78 2.81 5.58 8.06 8.40 8.48 8.56 8.68 8.73
359.7 355.9 179.2 124.1 119.0 117.9 116.8 115.2 114.5 .
4.61 4.66 9.26 13.39 13.95 14.08 14.21 14.41 14.49
0.3000 0.3250 0.6250 0.9250 0.9500 0.9600 0.9750 0.9900 1.0000
23.43 22.29 17.02 13.42 11.77 10.17 7.74 4.98 3.58 2.68
7.41 8.55 13.82 17.42 19.07 20.67 23.10 25.86 27.26 28.16
2.43 2.58 7.14 8.32 9.37 9.42 9.86 9.95 . .
4.03 4.29 11.86 13.82 15.56 15.80 16.37 16.52
0.2500 0.2750 0.8000 0.9500 1.0500 1.0750 1.1200 1.1250
24.51 23.83 17.51 13.14 11.27 11.10 8.07 4.84 3.72 2.56
7.45 8.13 14.45 18.82 20.69 20.86 23.89 27.12 28.24 29.40
2.25 2.40 8.00 9.21 9.64 10.06 10.25 10.37 . .
3.73 3.98 13.28 15.29 16.00 16.71 17.02 17.22
0.2500 0.2700 0.9000 1.0500 1.1000 1.1500 1.1700 1.2000
]nteffacial tension (30 (dyn/cm)
Petroleum-ether/water system 1.0 5.0 2.0 5.0 8.0 2.0 8.0
x x x x x x x
10 -6 10-6 10 -5 10-5 10 -5 10 -4 10-4
M M M M M M M
Benzene/water system 1.0 5.0 2.0 5.0 8.0 1.0 2.0 5.0 8.0 1.0
x x x x x x × x x ×
10 -5 10-5 10 -5 10 -5 10-5 10-4 10 -4 10 -4 10-4 10 -3
M M M M M M M M M M
.
.
.
Toluene/water system 1.0 5.0 2.0 5.0 8.0 1.0 2.0 5.0 8.0 1.0
x x x x x x x x x x
10-n 10-5 10-5 10 -5 10-5 10-4 10 -4 10 -4 10-4 10-8
M M M M M M M M M M
. .
411.5 387.6 140.3 120.2 106.7 106.2 101.4 100.5 . .
. .
444.4 416.7 125.0 108.6 103.7 99.8 97.9 97.8 . .
. .
Xylene/water system 1.0 5.0 2.0 5.0 8.0 1.0 2.0 5.0 8.0 1.0
x x x x x x x x x x
10 -5 M 10 -6 M 10 5 M 10 -2 M 10 -5 M 10 4 M 10-4 M 10 -4 M 10-4 M 10-3 M
. .
Journal of Colloid and Interface Science, Vol. 64, No. 1, March 15, 1978
182
NOTES
ol a.
:4
d
-4
d
3
4
-6
LOG.
-~
-4.
-3
CONC
Fro. 1. Curves showing the variation in interracial tension with concentrations of sodium deoxycholate in presence of (a) Q 0.1 M NaC1, • 1.0 M NaCI for benzene; & 0.1 M NaC1, [] 1.0 M NaC1 for toluene/water system. (b) E) 0 . 1 M NaCI, • 1.0M NaC1 for Xylene; A 0 . 1 M NaCI, [] 1.0 M NaCI for petroleum-ether system.
IV
b
A R E A - A~
o
:~o 200
460
~o
I00
eoo
FIG. 2. Curves showing the variation of surface pressure (rr) with Area (A) in presence of 0.1 M NaC1 for × pet.-ether, [] benzene, Q toluene, and A xylene systems. Journal of Colloid and Interface Science, Vol. 64, No. 1, March 15, 1978
2OO
300
4O0
AREA A2
FtG. 3. Curves showing the variation of surface pressure (zr) with Area (A) in presence of 1.0 M NaC1 for × pet.-ether, [] benzene, (3 toluene, and A xylene systems.
NOTES
0
4-0
~,0
120~
FIG. 4. Curves showing the distribution of charge in different layers with surface potential tOo. I, (os/ev) × 10-13; II, (~rJev) x 10-13; III, (tr/ev) x 10-13, inpresence of 0.1 M NaC1; IV, (~rl/ev) x 10-13; V, (trJev) x 10-I3; and VI, (tr/ev) x 10 13 in presence of 1.0 M NaC1.
183
with increasing concentrations of sodium deoxycholate. Initially the decrease was less at lower concentrations of sodium deoxycholate and greater on increasing concentrations. The decrease in interfacial tension was greater in the case of 1.00 M NaCI than in the case of 0.10 M NaC1. The surface pressures (It) have been evaluated by subtracting various values of interfacial tension from the values of interfacial tension for clean interfaces. The curves between surface pressure and area 0 r - A ) have been plotted in Figs. 2 and 3. The decrease in area was sharp at low surface pressure due to the study crowding of sodium deoxycholate molecules. Moreover, the molecules have been closely packed in the region in which a large change in surface pressure was observed. The values o f surface excess (F~) and number of molecules adsorbed per square centimeter have also been calculated with the help of interfacial tensionlog molar concentration curves. The relevant data are recorded in Tables I and II. It is evident from these above tables that initially the increase in surface excess (F~) was sharp with the increase in concentration of sodium deoxycholate. The values of surface excess are almost constant for all systems from concentration 5.0 x 10.5 to 1.0 x 10-3 M. The experimental values of surface potential (tOo) corresponding to the amount of the adsorbed molecules, determined experimentally, were noted with the help of the theoretical curves (Fig. 4). It
amount of adsorbent (o/e) and surface potential (tOo) for uni-univalent electrolytes in Fig. 4. The amount of adsorbent (o/e) can also be evaluated experimentally with the help of interracial tension using the following relations:
Fs
=
-(l/RT)(dy/d In C)
[5]
[I
I
and
~r = evFs.
[6]
=9 x
With the help of the theoretical curve between (o/e) and too, the values of tOo satisfying the experimentally determined value of (o/e) are noted and recorded in Tables I & II.
Results
and Discussion
The interracial tension at varying concentrations of sodium deoxycholate and sodium chloride have been evaluated for petroleum-ether/water, benzene/water, toluene/water, and xylene/water systems at 20°C and plotted in Fig. 1. The values of interfacial tensions for clean interfaces were found to be 20.28, 29.30, 30.84, and 31.96 dyn/cm for petroleum-ether/water, benzene/water, toluene/water, and xylene/water systems, respectively. It is evident from Fig. 1 that a regular decrease in in~erfacia! tension was observed
o
20
60
40
80
-~ffo-
FIG. 5. Curves showing the variation of surface excess Fs x 1011 with surface potential tOo in presence of I, 0.1 M NaC1 and II, 1.0 M NaC1 for [] petroleumether, C) benzene, x toluene, and Sx xylene/water systems. Journal of Colloid and Interface Science,
Vol. 64, N o . l, M a r c h 15, 1978
184
NOTES
is evident that the surface potential increases as the concentration of sodium deoxycholate increases which shows the increase in the stability of the systems. The increase in surface potential at lower concentration of sodium deoxycholate is greater than that of higher concentration. Therefore, a slight increase in the stability of systems was found at higher concentrations of emulsifier. The values of surface potential (~0) have been found to be higher in the presence of 0.1 M NaCI than in the presence of 1.0 M NaCI for the same concentration of sodium deoxycholate. These low values of surface potential in the case of 1.0M NaC1 are due to the presence of an excess amount of NaC1 which was responsible for the reduction of surface potential of the system. The values of the surface excess (Fs) were plotted against the surface potential in Fig. 5. It is obvious that all the points fall on the same curve for all the liquid/liquid systems, which indicates that the surface potentials were independent of the nature of the nonaqueous phase molecules. ACKNOWLEDGMENTS
4. Barry, B. W., and Gray, G. M. T., J. Colloid Interface Sci. 52, 314 (1975). 5. Barry, B. W., and Gray, G. M. T., J. Colloid Interface Sci. 52, 327 (1975). 6. Sastry, T. G., and Srivastava, S. N., Bull. Chem. Soc. Japan 42, 291 (1968). 7. Sastry, T. G., and Srivastava, S. N.,Ind. J. Chem. 6, 728 (1968). 8. Sastry, T. G., and Srivastava, S. N., J. Colloid Interface Sci. 33, 468 (1970). 9. Van deenen et al., J. Pharm. Pharmacol. 14, 429 (1962). 10. Shah, D. J., and Schulman, J. H., J. Lipid Res. 6, 341 (1965). 11. Ghatak, S., and Krishnamurty, C. R., J. Sci. Ind. Res. 14A, 285 (1955). 12. "International Critical Tables," Vol. IV, pp. 435, McGraw-Hill New York, 1929. 13. Stern, 0., Z. Electrochem. 30, 508 (1924). 14. Vold, R. D., J. Colloid Sci. 16, 1 (1961). 15. Derjaguin, B., and Kussakov, M., Acta Phys. Chem. URSS 10, 75, 153 (1939). 16. Schenkel, J. N., and Kitchener, J. A., Trans. Faraday Soc. 56, 161 (1960).
The authors are very grateful to the authorities of U. G. C., New Delhi, for granting financial assistance.
M. K. SHARMA
MEERA SHARMA S. P. JAIN S. N. SRIVASTAVA
REFERENCES 1. Kelvin, H., Leech (Johennesb.) 36, 108 (1966). 2. Trillo, J. M., Fernandez, S. G., and Pedrero, P. S., J. Colloid Interface Sci. 26, 518 (1968). 3. Haydon, D. A., J. Amer. Oil Chem. Soc. 45, 230 (1968).
Journal of Colloid and Interface Science, Vol. 64, No. 1, March 15, 1978
Chemical Laboratories Agra College Agra 282002, India Received December 1, 1976; accepted August 13, 1977