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Viscosity of oil and surfactant binary solution
Colloids and Surfaces A: Physicochemical and Engineering Aspects 175 (2000) 263 – 266 www.elsevier.nl/locate/colsurfa
Viscosity of oil and surfactant binary solution Zhen Zhou *, Midan Li, Heliang Yan Department of Printing Technology and Packaging Engineering, Beijing Institute of Printing, Beijing 102600, PR China
Abstract Viscosities were measured on binary solutions of oils and nonionic surfactants as functions of concentrations of the surfactant. The curves obtained show that there exist two configurations in these binary solutions. The results can determine which oil and surfactant can be combined to form reverse micelle and organize a W/O microemulsion. © 2000 Elsevier Science B.V. All rights reserved. Keywords: Viscosity; Nonionic surfactant; Oil; Reverse micelle; Microemulsion
1. Introduction The properties of surfactant micelle solutions (aqueous solutions of surfactants) have been extensively studied theoretically and experimentally. However, the properties of surfactants in nonaqueous media are still less studied. In the present work, we studied the viscosities of the surfactants’ and oils’ binary solutions. The viscosities of the binary solutions have been measured by a capillary viscosimeter. The results obtained show some of the binary solutions can form reverse micelles and some of the others cannot. Theoretically Israelachvili [1] analyzes all the interactions between surfactants and oils and/or surfactants and water. From the geometric packing considerations he suggests the following parameter can determine if a surfactant favors a micelle or a reverse micelle. * Corresponding author.
The parameter is the packing parameter V/acl0, a dimensionless value of a surfactant. V is the effective hydrocarbon volume of the surfactant, lc is the fully extended chain length of the surfactant and ac is the headgroup area of the surfactant. When V/acl0 \ 1, it will determine the surfactants forming reverse micelles and when V/acl0 B 1, it will determine the surfactants forming micelles or bilayers. In the present experimental work, all surfactants chosen are oil soluble nonionic surfactants. The systems studied are: cyclohexane and oleic acid, nonane and Span-80, castor oil and Span-80, castor oil and Tween-65, heptane and Tween-65, castor and oleic acid, lanolin and Span-85. In reference [2], Tadros presented the viscoelastic properties of the suspensions. When surfactants’ molecules are assembled as reverse micelles in oils’ media, the diameters of the reverse micelle droplets will become larger than the diameters of the surfactants’ molecules. The viscosities of these solutions will be higher than the pure oils. They
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Z. Zhou et al. / Colloids and Surfaces A: Physicochem. Eng. Aspects 175 (2000) 263–266
will follow Einstein’s formula when the volume fraction of the surfactants is quite low: h =h0(1+ 2.5f)
f B0.02
where h is the viscosity of a solution and h0 is the viscosity of the continuous phases. When the viscosities of these solutions are higher than the viscosities of those continuous phases, we are reasonable to find reverse micelles droplets. The data measured show some combinations of oils and surfactants can form reverse micelles. A reverse micelle solution is ready to form a W/0 microemulsion since the reverse micelle solution can extract dissolved water from the solvent and transfer it into the center of the reverse micelle. We hope this work could serve as a method to determine which kind of oils and surfactants will combine to form W/O microemulsions experimentally.
2. Material and methods
2.1. Materials The chemical reagents for this study are castor oil (from Beijing Yili Fine Chemical Co.), cyclohexane, nonane, heptane (all three from Beijing Chemical Factory), Span-80, Span-85, Tween-65 (all three from Beijing Donghuan United Chemical Factory), lanolin, oleic acid (both from Beijing Jinlong Chemical Co.). They are all chemically pure.
where Ws and W0 are the weights of a surfactant and oil. Viscosities h measured are functions of concentrations C. The surfactants concentrations varied in the interval: 00C00.194 (for Tween-65 in heptane), 00C01 (for oleic acid in cyclohexane) 00C00.4 (for Span-80 in nonane) 00C01 (for Span-80 in castor oil) 00C01 (for Tween-65 in castor oil) 00C01 (for Span-85 in lanolin) 00C01 (for oleic acid in castor oil)
2.3. Efflux times measurements After three days in the laboratory, the viscosities of these samples were measured by a Ostwald capillary viscosimeter (Hongqi Glass Instrument Factory, Yangzhou, China). Prior to the measurements, the capillary was flushed with acetone and kept at a desired temperature in a water bath. The solutions were given 15 min to equilibrate with the bath. The temperature of the bath oscillated around the mean value with an amplitude of 0.01°C. The time measurements were repeated five times in order to obtain accuracy. The density measurements of the solutions were performed with a densimeter (DMA 602, Anton Taar, Austria). 3. Results and discussion
2.2. Binary solution preparation The binary systems studied in the present paper are: cyclohexane and oleic acid, nonane and Span80, castor oil and Span-80, castor oil and Tween65, heptane and Tween-65, castor and oleic acid, lanolin and Span-85. Binary solutions were prepared by mixing proper amounts of oils and surfactants with magnetic agitator. The concentration C of a surfactant was calculated as follows: C= Ws/(Ws +W0)
Based on the measured efflux times the viscosities of these binary solutions can be calculated from the following equation: h= Adt where A is the parameter of the capillary viscosimeter, d is the density of the binary solutions and t is the efflux time of the solutions. The characterization of two surfactant configurations in oil media were obtained by the analysis of the viscosities with increasing the concentrations of the surfactants.
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The viscosities show continuous increases in Figs. 1–3 with increasing concentrations, reaching the viscosity value of the surfactant with concentration C= 1 in Fig. 2, but non-Newtonian flow behavior. At the very low concentration ranges
Fig. 4. Viscosities of castor oil and Span-80 solutions as functions of concentrations of Span-80 (T=20°C).
Fig. 1. Viscosities of heptane and Tween-65 solutions as functions of concentrations of Tween-65 (T= 20°C).
Fig. 5. Viscosities of castor oil and Tween-65 solutions as functions of concentrations of Tween 65 (T= 20°C).
Fig. 2. Viscosities of cyclohexane and oleic acid solutions as functions of concentrations of oleic acid (T= 20°C).
Fig. 3. Viscosities of nonane and Span-80 solutions as functions of concentrations of Span-80 (T= 20°C).
these curves show linear behavior corresponding with the Einstein approximation (the range is not specified in those curves). Then, they increased fast showing nonlinear behavior. The reverse micelles have formed in these combinations (the determinations of CMC values of these systems are in progress). The differentiation from the above configuration (see Figs. 4–7) was achieved with the same viscosity measurements between the components. All of these curves show an unusual rheological properties for these binary solutions and a nonNewtonian flow behavior on all the ranges of the concentrations. In Figs. 4 and 5, the viscosities decrease at the beginning of the curves, then reach a minimal value that is even lower than the pure oil and the pure surfactant. This phenomenon is due to the
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Z. Zhou et al. / Colloids and Surfaces A: Physicochem. Eng. Aspects 175 (2000) 263–266
Fig. 6. Viscosities of lanolin and Span-85 solutions as functions of concentrations of Span-85 (T= 20°C).
Fig. 7. Viscosities of castor oil and oleic acid solutions as functions of concentrations of oleic acid (T = 20°C).
surfactants’ molecules are well dispersed in the oils’ media since the dispersed energy is always bigger than associated energy [3]. No structures can be found in these systems. The same conclusion we can also have from the analysis of the Einstein’s formula. The minimal value of the viscosities must correspond to the maximum dispersion energy. The rising of the viscosities after the minimal values is because of the more amounts of surfactants added in the binary solutions. For surfactant molecules, the number of nearest neighbouring oils molecules decrease. The interactions between surfactants’ molecules are bigger than those between oils. But there is no structure existed in this interval since the viscosities are smaller than the pure surfactants’ viscosities. One can find a continuously decreasing of the viscosities with the increasing concentrations in Figs. 6 and 7. There is no minimal viscosity value. The fact means the interactions between the surfactants’ molecules are smaller than those between oils. There are no structures existing in these cases. In last two cases, the surfactants are soluble liquids dispersed in oil media without structure formations.
4. Conclusions
.
Because of the complex interactions between oil and surfactants molecules, there exist two configurations in these binary solutions. In the first one, reverse micelles have formed. In the second one, the surfactants’ molecules are not self assembled as reverse micelles, but only dispersed in oil media. We can expect a W/O microemulsion can form in the first configuration when water added into the surfactant and oil binary solution. There will be no W/O microemulsion formed when the surfactants’ molecules dispersed in oil media. A simple experimental method to determine which oil and surfactant can be combined to form a reverse micelle and organize a W/O microemulsion, has been described.
References [1] J. Israelachvili, Colloids Surfaces A: Physicochem. Eng. Asp. 91 (1994) 1 – 8. [2] Th.F. Tadros, Adv. Colloid Interface Sci. 68 (1996) 97– 200. [3] J. Israelachvili, Intermolecular and Surface Forces, Acadamic Press, London, 1985, pp. 112 – 114.
Viscosity of oil and surfactant binary solution Zhen Zhou *, Midan Li, Heliang Yan Department of Printing Technology and Packaging Engineering, Beijing Institute of Printing, Beijing 102600, PR China
Abstract Viscosities were measured on binary solutions of oils and nonionic surfactants as functions of concentrations of the surfactant. The curves obtained show that there exist two configurations in these binary solutions. The results can determine which oil and surfactant can be combined to form reverse micelle and organize a W/O microemulsion. © 2000 Elsevier Science B.V. All rights reserved. Keywords: Viscosity; Nonionic surfactant; Oil; Reverse micelle; Microemulsion
1. Introduction The properties of surfactant micelle solutions (aqueous solutions of surfactants) have been extensively studied theoretically and experimentally. However, the properties of surfactants in nonaqueous media are still less studied. In the present work, we studied the viscosities of the surfactants’ and oils’ binary solutions. The viscosities of the binary solutions have been measured by a capillary viscosimeter. The results obtained show some of the binary solutions can form reverse micelles and some of the others cannot. Theoretically Israelachvili [1] analyzes all the interactions between surfactants and oils and/or surfactants and water. From the geometric packing considerations he suggests the following parameter can determine if a surfactant favors a micelle or a reverse micelle. * Corresponding author.
The parameter is the packing parameter V/acl0, a dimensionless value of a surfactant. V is the effective hydrocarbon volume of the surfactant, lc is the fully extended chain length of the surfactant and ac is the headgroup area of the surfactant. When V/acl0 \ 1, it will determine the surfactants forming reverse micelles and when V/acl0 B 1, it will determine the surfactants forming micelles or bilayers. In the present experimental work, all surfactants chosen are oil soluble nonionic surfactants. The systems studied are: cyclohexane and oleic acid, nonane and Span-80, castor oil and Span-80, castor oil and Tween-65, heptane and Tween-65, castor and oleic acid, lanolin and Span-85. In reference [2], Tadros presented the viscoelastic properties of the suspensions. When surfactants’ molecules are assembled as reverse micelles in oils’ media, the diameters of the reverse micelle droplets will become larger than the diameters of the surfactants’ molecules. The viscosities of these solutions will be higher than the pure oils. They
0927-7757/00/$ - see front matter © 2000 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 7 - 7 7 5 7 ( 0 0 ) 0 0 6 2 2 - 1
264
Z. Zhou et al. / Colloids and Surfaces A: Physicochem. Eng. Aspects 175 (2000) 263–266
will follow Einstein’s formula when the volume fraction of the surfactants is quite low: h =h0(1+ 2.5f)
f B0.02
where h is the viscosity of a solution and h0 is the viscosity of the continuous phases. When the viscosities of these solutions are higher than the viscosities of those continuous phases, we are reasonable to find reverse micelles droplets. The data measured show some combinations of oils and surfactants can form reverse micelles. A reverse micelle solution is ready to form a W/0 microemulsion since the reverse micelle solution can extract dissolved water from the solvent and transfer it into the center of the reverse micelle. We hope this work could serve as a method to determine which kind of oils and surfactants will combine to form W/O microemulsions experimentally.
2. Material and methods
2.1. Materials The chemical reagents for this study are castor oil (from Beijing Yili Fine Chemical Co.), cyclohexane, nonane, heptane (all three from Beijing Chemical Factory), Span-80, Span-85, Tween-65 (all three from Beijing Donghuan United Chemical Factory), lanolin, oleic acid (both from Beijing Jinlong Chemical Co.). They are all chemically pure.
where Ws and W0 are the weights of a surfactant and oil. Viscosities h measured are functions of concentrations C. The surfactants concentrations varied in the interval: 00C00.194 (for Tween-65 in heptane), 00C01 (for oleic acid in cyclohexane) 00C00.4 (for Span-80 in nonane) 00C01 (for Span-80 in castor oil) 00C01 (for Tween-65 in castor oil) 00C01 (for Span-85 in lanolin) 00C01 (for oleic acid in castor oil)
2.3. Efflux times measurements After three days in the laboratory, the viscosities of these samples were measured by a Ostwald capillary viscosimeter (Hongqi Glass Instrument Factory, Yangzhou, China). Prior to the measurements, the capillary was flushed with acetone and kept at a desired temperature in a water bath. The solutions were given 15 min to equilibrate with the bath. The temperature of the bath oscillated around the mean value with an amplitude of 0.01°C. The time measurements were repeated five times in order to obtain accuracy. The density measurements of the solutions were performed with a densimeter (DMA 602, Anton Taar, Austria). 3. Results and discussion
2.2. Binary solution preparation The binary systems studied in the present paper are: cyclohexane and oleic acid, nonane and Span80, castor oil and Span-80, castor oil and Tween65, heptane and Tween-65, castor and oleic acid, lanolin and Span-85. Binary solutions were prepared by mixing proper amounts of oils and surfactants with magnetic agitator. The concentration C of a surfactant was calculated as follows: C= Ws/(Ws +W0)
Based on the measured efflux times the viscosities of these binary solutions can be calculated from the following equation: h= Adt where A is the parameter of the capillary viscosimeter, d is the density of the binary solutions and t is the efflux time of the solutions. The characterization of two surfactant configurations in oil media were obtained by the analysis of the viscosities with increasing the concentrations of the surfactants.
Z. Zhou et al. / Colloids and Surfaces A: Physicochem. Eng. Aspects 175 (2000) 263–266
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The viscosities show continuous increases in Figs. 1–3 with increasing concentrations, reaching the viscosity value of the surfactant with concentration C= 1 in Fig. 2, but non-Newtonian flow behavior. At the very low concentration ranges
Fig. 4. Viscosities of castor oil and Span-80 solutions as functions of concentrations of Span-80 (T=20°C).
Fig. 1. Viscosities of heptane and Tween-65 solutions as functions of concentrations of Tween-65 (T= 20°C).
Fig. 5. Viscosities of castor oil and Tween-65 solutions as functions of concentrations of Tween 65 (T= 20°C).
Fig. 2. Viscosities of cyclohexane and oleic acid solutions as functions of concentrations of oleic acid (T= 20°C).
Fig. 3. Viscosities of nonane and Span-80 solutions as functions of concentrations of Span-80 (T= 20°C).
these curves show linear behavior corresponding with the Einstein approximation (the range is not specified in those curves). Then, they increased fast showing nonlinear behavior. The reverse micelles have formed in these combinations (the determinations of CMC values of these systems are in progress). The differentiation from the above configuration (see Figs. 4–7) was achieved with the same viscosity measurements between the components. All of these curves show an unusual rheological properties for these binary solutions and a nonNewtonian flow behavior on all the ranges of the concentrations. In Figs. 4 and 5, the viscosities decrease at the beginning of the curves, then reach a minimal value that is even lower than the pure oil and the pure surfactant. This phenomenon is due to the
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Z. Zhou et al. / Colloids and Surfaces A: Physicochem. Eng. Aspects 175 (2000) 263–266
Fig. 6. Viscosities of lanolin and Span-85 solutions as functions of concentrations of Span-85 (T= 20°C).
Fig. 7. Viscosities of castor oil and oleic acid solutions as functions of concentrations of oleic acid (T = 20°C).
surfactants’ molecules are well dispersed in the oils’ media since the dispersed energy is always bigger than associated energy [3]. No structures can be found in these systems. The same conclusion we can also have from the analysis of the Einstein’s formula. The minimal value of the viscosities must correspond to the maximum dispersion energy. The rising of the viscosities after the minimal values is because of the more amounts of surfactants added in the binary solutions. For surfactant molecules, the number of nearest neighbouring oils molecules decrease. The interactions between surfactants’ molecules are bigger than those between oils. But there is no structure existed in this interval since the viscosities are smaller than the pure surfactants’ viscosities. One can find a continuously decreasing of the viscosities with the increasing concentrations in Figs. 6 and 7. There is no minimal viscosity value. The fact means the interactions between the surfactants’ molecules are smaller than those between oils. There are no structures existing in these cases. In last two cases, the surfactants are soluble liquids dispersed in oil media without structure formations.
4. Conclusions
.
Because of the complex interactions between oil and surfactants molecules, there exist two configurations in these binary solutions. In the first one, reverse micelles have formed. In the second one, the surfactants’ molecules are not self assembled as reverse micelles, but only dispersed in oil media. We can expect a W/O microemulsion can form in the first configuration when water added into the surfactant and oil binary solution. There will be no W/O microemulsion formed when the surfactants’ molecules dispersed in oil media. A simple experimental method to determine which oil and surfactant can be combined to form a reverse micelle and organize a W/O microemulsion, has been described.
References [1] J. Israelachvili, Colloids Surfaces A: Physicochem. Eng. Asp. 91 (1994) 1 – 8. [2] Th.F. Tadros, Adv. Colloid Interface Sci. 68 (1996) 97– 200. [3] J. Israelachvili, Intermolecular and Surface Forces, Acadamic Press, London, 1985, pp. 112 – 114.