Phase Diagrams, Density, and Viscosity for the Pseudoternary System of

Jun 12, 2012 - then inversion, to the state of oil-in-water, viscosity is very sensitive to ..... Funding. This project was funded by the Priority Aca...
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Phase Diagrams, Density, and Viscosity for the Pseudoternary System of {Propan-2-yl Tetradecanoate (IPM) (1) + [Tween 80 (21) + Propan-1-ol (22)] (2) + Water (3)} Miao Zhang, Yuan-Yuan Wang, and Tong-Chun Bai* College of Chemistry, Chemical Engineering and Materials Science, Soochow University, Suzhou, 215123, China ABSTRACT: In this work, a microemulsion system composed of propan-2-yl tetradecanoate (IPM) as oil, polyoxyethylene (20) sorbitan monooleate (Tween 80) as surfactant, propan-1-ol as cosurfactant, and water as the hydrophilic phase has been prepared. The pseudoternary phase diagram of {IPM (1) + [Tween 80 (21) + propan-1-ol (22)] (2) + water (3)} at 303.15 K has been constructed at a constant surfactant to cosurfactant mass ratio of 0.5:1. The phase diagram shows the area of microemulsion. Densities and viscosities were measured in the microemulsion area along three water dilution lines. A maximum viscosity is observed along the water dilution line, which indicates a structural transition from water-in-oil, to a bicontinuous state, and then inversion, to the state of oil-in-water.

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INTRODUCTION Microemulsions are transparent and thermodynamically stable and have a droplet size of < 150 nm.1 In pharmaceutical applications, the commonly used components composed of microemulsions, such as oil, surfactant, and cosurfactant, are usually good permeation enhancers. In particular, microemulsions have a powerful solubilization ability for poorly water-soluble drugs. By using the microemulsion of water-in-oil or oil-in-water, drugs were encapsulated in the nanodroplets, and their solubility and bioavailability were improved significantly.2−4 All of these merits of microemulsion show the significant enhancement effect on transdermal delivery over conventional formulation and hence demonstrate its wide used in pharmaceutical drug delivery techniques. The microemulsion system is usually characterized by the construction of pseudoternary phase diagrams, dynamic light scattering (DLS), transmission electron microscopy (TEM), viscosity, and conductivity measurements. The effects of composition on the state of microemulsion and on their microstructure have been the objectives of researchers. For some newly formulated drug carrier microemulsions, the phase diagram and their relative physical properties were necessarily reported.2−4 From these properties, some new perspectives on what possible structural changes may be taking place have been given.5−8 Among these measurements, viscosity is one simple and sensitive method, because the structural transition is reflected in the variation of viscosity with composition. The viscosity of a microemulsion is governed by two opposing effects: increasing the water content is expected to lower the viscosity, while decreasing the amount of surfactant and cosurfactant increases interfacial tension between oil and water, decreases interfacial area, increases the size of the internal domains, and therefore increases viscosity.4 In the process of © 2012 American Chemical Society

structural transition from water-in-oil to the bicontinuous, and then inversion, to the state of oil-in-water, viscosity is very sensitive to the variation of composition, and usually a maximum is shown at the transition state.6−8 Propan-2-yl tetradecanoate, (commonly known as isopropyl myristate, given the acronym IPM) is used in cosmetic and pharmaceutical formulations for its hydrophobic property. Polyoxyethylene (20) sorbitan monooleate (commonly known as Tween 80) is a nonionic surfactant and is widely used in foods and pharmaceutical formulations.9,10 The microemulsion systems composed of Tween 80 and IPM have been found to be useful in encapsulating drugs.2 Regarding to cosurfactants, short-chain alcohols are the most commonly used component in microemulsion formulations.8 A higher alcohol content leads to a broadened microemulsion (ME) region and a diminished emulsion region in the phase diagram and results in the formation of system with smaller particle sizes and lower viscosities. The phase diagram of some microemulsions and drug delivery systems have been reported in literature, but less report on the data of equilibrium and viscosity. In present work, a microemulsion system composed of IPM as oil, Tween 80 as surfactant, propan-1-ol as cosurfactant, and water as the hydrophilic phase is studied. The cosurfactant (propan-1-ol) is used to bring the one-phase microemulsion region into an experimental window of composition and temperature. The pseudoternary phase diagram of system of {IPM (1) + [Tween 80 (21) + propan-1-ol (22)] (2) + water (3)} with a constant surfactant to cosurfactant mass ratio of Received: March 14, 2012 Accepted: May 30, 2012 Published: June 12, 2012 2023

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where the surfactant-to-cosurfactant mass ratio of 0.5 was fixed at a constant. Then the pseudobinary mixtures were diluted with water. In this way, the mass ratio of (surfactant + cosurfactant) w2 to oil w1 keeps constant along the water dilution line. This character of w1/w2 is used to mark the water dilution in this article. Density Measurement. The samples of the homogeneous microemulsion phase were prepared as shown in the viscosity measurement. Densities were measured with an Anton Paar DMA 602 vibrating tube densimeter with an uncertainty of ± 0.00005 g·cm−3. The temperature of the cell was controlled by circulating water from a water bath with the temperature within ± 0.01 K. The densimeter was calibrated by the twicedistilled deionized water, and it was degassed before use.

0.5 at 303.15 K was measured. The viscosity and density of the microemulsion phase were measured for its composition along three water dilution lines. The effect of the mass fraction of water on viscosity and density was analyzed, and the effect on the structural transition was discussed.

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EXPERIMENTAL SECTION Materials. Propan-2-yl tetradecanoate (commonly known as isopropyl myristate, given the acronym IPM; CAS No.: 110-27-0) analytical agent grade with a purity of mass fraction 0.98 was used as the lipophilic phase. Polyoxyethylene (20) sorbitan monooleate (commonly known as Tween 80 or polysorbate 80, CAS No. 9005-65-6), analytical agent grade with a purity of 0.99, was used as a surfactant. Propan-1-ol (CAS No. 71-23-8), analytical agent grade with a purity of 0.99, was used as cosurfactant. All chemicals were supplied by Sinopharm Chemical Reagent Co. Ltd. and were used without further purification. Twice-distilled, deionized water was used as the hydrophilic phase. Phase Equilibrium Determination. Pseudoternary phase diagrams of oil, distilled water, and cosurfactant + surfactant mixtures were constructed at a fixed surfactant-to-cosurfactant mass ratio. The mass ratio of the two surfactants, Tween 80 to propan-1-ol, was kept constant over the whole determination. Phase diagrams were obtained by visual inspection of the mixtures of the ingredients, which were preweighed into glass vials, titrated with water, and stirred well. As a convenient method, the construction of the phase diagrams were done by drawing “water dilution lines” representing an increase of water content while decreasing the (surfactant + cosurfactant) and oil levels. In this work, water was titrated along dilution lines drawn from the water apex to the opposite surfactant side of the triangle. The line was denoted by the value of the line intersection with the surfactant scale. In the case that the solution was monophasic, clear and transparent mixtures were visualized after stirring; the samples were marked as points in the microemulsion region. In the case that turbidity appeared followed by a phase separation, the samples were considered biphasic and were marked as points in the phase equilibrium region. The area covered by the monophasic points was considered the microemulsion region. The temperature was controlled by a water bath to 303.15 ± 0.01 K. During the process of water titration, a microsyringe of 0.005 mL scale was used. Samples were weighed using an electronic balance (model BT25S, Sartorius AG, Beijing) to 0.01 mg. Three parallel determinations were performed. For samples of 10 g in total mass, the relative error of the phase equilibrium data is estimated to be 0.5 %. Viscosity Measurement. Viscosities of the homogeneous microemulsion phase were measured by a suspended level Ubbelohde viscometer. The efflux time of the fluid was measured with a digital stopwatch to ± 0.01 s. The viscometer was kept in a water thermostat controlled to ± 0.01 K. Viscometers were calibrated by the twice-distilled, deionized water. The water was degassed before calibration use. Detection was performed at least in six replicates for each composition at each temperature. The estimated relative standard deviation for viscosity was ± 0.2 %. Other experimental details and procedures are the same as those described in our previous work.11 To prepare the microemulsion samples for viscosity determination, several pseudobinary mixtures of {IPM(1) + [Tween 80 (21) + propan-1-ol (22)] (2)} were prepared first,

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RESULTS AND DISCUSSION Mass Ratio of Tween 80 to Propan-1-ol. To construct the phase diagram of a pseudoternary mixture and to investigate the structural transform with the change of water content, the mass ratio of surfactant (Tween 80) to

Figure 1. Variation of mass fraction of water (w3) against the mass ratio of w21/w22.

Figure 2. Phase diagram of the pseudoternary system of {IPM (1) + [Tween 80 + propan-1-ol] (2) + water (3)} at 303.15 K. ■, experimental data. The line is plotted by eq 1. 2024

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Table 4. Densities of the Pseudoternary Systems at T = 303.15 K Changing with the Mass Fraction of Water w3 along Three Water Dilution Lines A (w1/w2 = 0.15:0.85), B (w1/w2 = 0.20:0.80), and C (w1/w2 = 0.25:0.75), Each Line with a Constant Mass Ratio of w1/w2

Table 1. Equilibrium Compositions of System of {IPM (1) + [Tween 80 (21) + Propan-1-ol (22)] (2) + Water (3)} at 303.15 K with the Mass Ratio of w21/w22 = 0.5 w1

w2

w3

w1

w2

w3

0.787 0.699 0.668 0.564 0.442 0.400 0.380

0.213 0.262 0.286 0.376 0.442 0.420 0.467

0.000 0.039 0.046 0.060 0.116 0.131 0.153

0.319 0.216 0.162 0.104 0.060 0.026

0.479 0.503 0.487 0.433 0.345 0.230

0.201 0.281 0.351 0.463 0.595 0.744

Table 2. Parameters Ai and Their Errors δAi of Equation 1. The Correlation Coefficient R and the Standard Deviation s Are Obtained by Fitting the Phase Equilibrium Data of w1 and w3 A1

δA1

A2

δA2

R

s

−0.111

0.011

−1.93

0.031

0.9970

0.02

w3

ρ/g·cm−3

w3

ρ/g·cm−3

w3

ρ/g·cm−3

A 0 0.070 0.140 0.180 0.210 0.280 0.320 0.350 0.420 0.490

0.87279 0.88511 0.89806 0.90377 0.90853 0.91952 0.92454 0.92947 0.93772 0.94634

B 0 0.100 0.231 0.289 0.309 0.324 0.355 0.377 0.394 0.424

0.8697 0.88731 0.90846 0.91679 0.92011 0.92194 0.92503 0.92783 0.93017 0.93361

C 0 0.041 0.080 0.120 0.160 0.200 0.240 0.280 0.300 0.334

0.86658 0.87454 0.88151 0.8889 0.89485 0.90141 0.90732 0.91328 0.91604 0.92047

Table 5. Densities of the Pseudoternary Systems at T = 313.15 K Changing with the Mass Fraction of Water w3 along Three Water Dilution Lines A (w1/w2 = 0.15:0.85), B (w1/w2 = 0.20:0.80), and C (w1/w2 = 0.25:0.75), Each Line with a Constant Mass Ratio of w1/w2 w3

ρ/g·cm−3

w3

ρ/g·cm−3

w3

ρ/g·cm−3

A 0 0.070 0.140 0.180 0.210 0.280 0.320 0.350 0.420 0.490

0.86597 0.87785 0.88842 0.89503 0.89978 0.91041 0.91576 0.9202 0.92978 0.93882

B 0 0.100 0.231 0.289 0.309 0.324 0.355 0.377 0.394 0.424

0.86157 0.87987 0.90081 0.90958 0.91175 0.91341 0.9182 0.92025 0.92251 0.92582

C 0 0.041 0.080 0.120 0.160 0.200 0.240 0.280 0.300 0.334

0.85898 0.86659 0.87348 0.88045 0.8869 0.89294 0.89902 0.90465 0.90749 0.91095

Figure 3. Variation of compositions of the microemulsion phase along water dilution lines for measuring density and viscosity. The mass ratio of w1/w2 for ■, A; ▲, B; and ●, C is 0.15:0.85, 0.20:0.80, and 0.25:0.75, respectively.

Table 3. Densities of [IPM (1) + (Tween 80 + Propan-1-ol) (2)] and [(Tween 80 + Propan-1-ol) (2) + Water (3)] at (303.15 and 313.15) K ρ/g·cm−3 w1

303.15 K

IPM (1) + (Tween 80 + ol) (2) 0 0.88891 0.050 0.87969 0.099 0.87503 0.150 0.87179 0.200 0.86924 0.251 0.86655 0.300 0.86487 0.350 0.86314 0.380 0.86232 0.406 0.86158

313.15 K Propan-10.88039 0.87285 0.86672 0.86419 0.86136 0.85870 0.85677 0.85519 0.85446 0.85365

ρ/g·cm−3 w3

303.15 K

313.15 K

(Tween 80 + Propan-1-ol) (2) + Water (3) 0 0.88891 0.88039 0.070 0.89880 0.88988 0.140 0.90789 0.89900 0.210 0.91687 0.90811 0.280 0.92567 0.91794 0.350 0.93446 0.92620 0.420 0.94249 0.93493 0.490 0.95052 0.94341 0.560 0.95894 0.95128 0.630 0.96668 0.95925

Figure 4. Densities of [IPM(1) + (Tween 80 + propan-1-ol) (2)] as a function of w1 at ■, 303.15; and ●, 313.15 K. The lines are plotted by eq 2.

cosurfactant (propan-1-ol) should be determined first. This ratio is usually fixed at a constant throughout the whole measurement. In pharmaceutical applications, the microemulsion should not only encapsulate hydrophobic drug, but also it should be able to solubilize high amounts of water. A higher alcohol content usually leads to the microemulsion region broadening in the phase diagram and results in the 2025

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Table 6. Polynomial Parameters Di and Their Errors δDi of Equation 2, the Correlation Coefficient R, and the Standard Error s of the Fits Obtained by Fitting Densities for System of [IPM (1) + (Tween 80 + Propan-1-ol) (2)] T/K

D0

δD0

D1

δD1

D2

δD2

D3

δD3

R

s

303.15 313.15

0.88832 0.88015

0.0006 0.0005

−0.1754 −0.1644

0.013 0.011

0.496 0.431

0.081 0.069

−0.564 −0.464

0.13 0.11

0.9981 0.9986

0.0006 0.0005

w3 is at the place of w21/w22 = 0.5, which will be used as an optimum ratio for the construction of pseudoternary phase diagram and for the measurement of density and viscosity. Phase Diagram. A homogeneous solution composed of oil phase (IPM) and surfactant (Tween 80 + propan-1-ol) was formulated with a constant mass ratio of w21/w22 = 0.5. In the process of phase equilibrium determination, the mass ratio of IPM to (Tween 80 + propan-1-ol), w1/(w21 + w22), was set to 9:1, 8:2, 7:3, 6:4, 5:5, 4:6, 3:7, 2:8, and 1:9, respectively. These formulated mixtures were set as the original composition for water dilution and phase equilibrium determination. The phase diagram at 303.15 K is shown in Figure 2, and the experimental data are listed in Table 1. Interestingly, we found that the phase equilibrium data can be well-described by eq 1.

log(w1) = A1 + A 2 w3 Figure 5. Densities of pseudoternary mixtures varying with the mass fraction of water w3 at T = 303.15 K, along three water dilution lines with mass ratio (w1/w2) = ●, 0.15:0.85, A; ▲, 0.20:0.80, B; and ▼, 0.25:0.75, C. The densities of pseudobinary mixtures of [(Tween 80 + propan-1-ol) (2) + water (3)] is shown in ■, with mass ratio (w1/w2) = 0:1. The lines are plotted by eq 3.

(1)

The parameters and its errors of eq 1 were obtained by fitting equilibrium data and are listed in Table 2. At the present stage, we have not found a satisfactory theoretical model to describe the phase behavior of the microemulsion. The physical meaning of these parameters is just an empirical parameter. In Figure 2, the equilibrium line is plotted by eq 1. Density. For the microemulsion phase, densities were measured for samples with compositions along three water dilution lines as shown in Figure 3. The three initial compositions A (w1/w2 = 0.15:0.85), B (w1/w2 = 0.20:0.80), and C (w1/w2 = 0.25:0.75) were pseudobinary mixtures of [IPM(1) + (Tween 80 + propan-1-ol) (2)]. With water added, the composition changes from A, B, and C toward the water apex along three linear lines, respectively. The ratio of w1/w2 is a constant for each line. This character of w1/w2 is used to mark the water dilution lines. Densities of two pseudobinary mixtures of [(Tween 80 + propan-1-ol) (2) + water (3)] and [IPM(1) + (Tween 80 + propan-1-ol) (2)] and three pseudoternary mixtures of [IPM (1) + (Tween 80 + propan-1-ol) (2) + water (3)] at (303.15 and 313.15) K are listed in Tables 3 to 5, respectively. The mass ratio of Tween 80 to propan-1-ol is fixed at 0.5. The variation of density against the mass fraction of w1 for

formation of systems with smaller particle sizes and lower viscosities.8 To obtain the mass ratio, mixtures of Tween 80 and propan1-ol with the mass ratio of w21/w22 = 0.1, 0.5, 1.0, 1.5, and 2.0 were tested. The cosurfactant (propan-1-ol) is used to bring the one-phase microemulsion region into an experimental window of composition. The mass ratio of surfactant to cosurfactant was chosen to suit the application in pharmaceutical techniques. The test mixtures were mixed with equivalent weight IPM, respectively. In a equilibrium glass cell, the preweighed homogeneous mixed sample was titrated slowly by water until turbidity appears. The water concentration at equilibrium (w3) was calculated from the amount of water titrated. This amount is an index to evaluate the capacity of microemulsion to solubilize water and to broaden the area of microemulsion in phase diagram. Figure 1 shows the variation of water content (w3) against the weight ratio of w21/w22. The maximum value of

Table 7. Polynomial Parameters Di and Their Errors δDi of Equation 3, the Correlation Coefficient R, and the Standard Error s of the Fits Obtained by Fitting the Densities of Microemulsion Phases along Water Dilution Lines with Constant w1/w2 Mass Ratio w1/w2

D0

δD0

D1

0:1 0.15:0.85 0.20:0.80 0.25:0.75

0.88913 0.87269 0.86951 0.86671

0.0001 0.0003 0.0003 0.0001

0.1365 0.1888 0.1908 0.1930

0:1 0.15:0.85 0.20:0.80 0.25:0.75

0.88022 0.86595 0.86156 0.85889

0.0002 0.0001 0.0002 0.0001

0.1392 0.1695 0.1928 0.1922

δD1 303.15 K 0.001 0.002 0.003 0.002 313.15 K 0.001 0.001 0.002 0.002 2026

D2

δD2

R

s

−0.0216 −0.0771 −0.0937 −0.0959

0.001 0.005 0.007 0.006

0.9999 0.9997 0.9997 0.9999

0.0002 0.0003 0.0003 0.0002

−0.0216 −0.0422 −0.0972 −0.1051

0.002 0.003 0.006 0.007

0.9999 0.9999 0.9998 0.9998

0.0002 0.0002 0.0002 0.0002

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Table 8. Viscosities of Pseudo-Binary Mixtures of [IPM (1) + (Tween 80 + Propan-1-ol) (2)] and [(Tween 80 + Propan1-ol) (2) + Water (3)] at T = (303.15 and 313.15) K η/mPa·s w1

313.15 K

303.15 K

IPM (1) + (Tween 80 + Propan-1ol) (2) 0 7.58 8.19 0.041 7.42 8.00 0.080 7.28 7.80 0.115 7.15 7.62 0.147 7.06 7.48 0.150 7.04 7.48 0.178 6.94 7.41 0.194 6.90 7.30 0.206 6.87 7.22 0.232 6.79 7.15 0.250 6.74 7.09 0.257 6.73 7.06 0.280 6.66 6.99

η/mPa·s w3

313.15 K

303.15 K

(Tween 80 + Propan-1-ol) (2) + Water (3) 0 7.92 8.36 0.041 8.83 9.33 0.080 9.09 9.67 0.115 9.10 9.77 0.147 9.01 9.74 0.178 8.93 9.68 0.206 8.79 9.53 0.232 8.64 9.41

Figure 7. Viscosities of pseudoternary mixtures varying with the mass fraction of water w3 at T = 303.15 K, along three water dilution lines of mass ratio (w1/w2) = ■, 0.15:0.85, A; ●, 0.20:0.80, B; and ▲, 0.25:0.75, C. The viscosity of the pseudobinary mixture of [(Tween 80 + propan-1-ol) (2) + water (3)] is shown in ○ with mass ratio (w1/w2) = 0:1. The lines are plotted by eq 5.

Table 10. Viscosities η of the Pseudoternary System at T = 313.15 K Changing with the Mass Fraction of Water w3 along Three Water Dilution Lines A (w1/w2 = 0.15:0.85), B (w1/w2 = 0.20:0.80), and C (w1/w2 = 0.25:0.75), Each Line with a Constant Mass Ratio of w1/w2 w3

η/mPa·s

A 0 0.106 0.191 0.262 0.315 0.362 0.402 0.429 0.454 0.477 0.498 0.518 0.536 0.553 0.568 0.583

Figure 6. Viscosities of pseudobinary mixtures of [IPM (1) + (Tween 80 + propan-1-ol) (2)] changing with the mass fraction of IPM w1 at T = ■, 303.15 K; and ●, 313.15 K. The lines are plotted by eq 4.

[IPM (1) + (Tween 80 + propan-1-ol) (2)] are shown in Figure 4, in which density decreases with the increase in w1. In this situation, the data can be fitted by a polynomial equation ρ /g·cm−3 = D0 + D1w1 + D2w12 + D3w13

(2)

w3

η/mPa·s

w3

B 7.04 7.56 8.05 8.32 8.53 8.68 8.82 8.89 8.92 8.96 8.94 8.92 8.87 8.78 8.68 8.61

0 0.102 0.185 0.254 0.312 0.347 0.379 0.407 0.433 0.457 0.479 0.499 0.518 0.535

η/mPa·s

C 6.91 7.46 8.04 8.46 8.85 9.08 9.24 9.43 9.50 9.58 9.63 9.62 9.56 9.45

0 0.0914 0.183 0.232 0.287 0.335 0.365 0.414 0.430 0.460 0.490

6.74 7.33 7.91 8.22 8.82 9.47 9.94 10.35 10.43 10.54 10.51

the addition of IPM. In these cases, the density data can be fitted by eq 3.

The parameters and the fitting errors are provided in Table 6. For systems of [(Tween 80 + propan-1-ol) (2) + water (3)] and pseudoternary mixtures, the variation of density versus the mass fraction of water (w3) is shown in Figure 5. Because the density behaviors at (313.15 and 303.15) K are similar, only the data at 303.15 K are shown. In Figure 5, the density increases with the increase in w3 and decreases with

ρ /g·cm−3 = D0 + D1w3 + D2w32

(3)

The parameters and the fitting errors are provided in Table 7. Viscosity. The viscosities of two pseudobinary mixtures of [(Tween 80 + propan-1-ol) (2) + water (3)] and [IPM (1) + (Tween 80 + propan-1-ol) (2)] are listed in Table 8, where the

Table 9. Parameters Bi and Their Errors δBi of Equation 4, the Correlation Coefficient R, and the Standard Deviation s of the Fits Obtained by Fitting the Viscosity for the System of [IPM (1) + (Tween 80 + Propan-1-ol) (2)] T/K

B0

δB0

B1

δB1

B2

δB2

R

s

313.15 303.15

7.580 8.199

0.005 0.016

−3.99 −5.31

0.07 0.2

2.56 3.46

0.2 0.8

0.9995 0.9977

0.006 0.019

2027

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Table 11. Viscosities η of the Pseudoternary System at T = 303.15 K Changing with the Mass Fraction of Water w3 along Three Water Dilution Lines A (w1/w2 = 0.15:0.85), B (w1/w2 = 0.20:0.80), and C (w1/w2 = 0.25:0.75), Each Line with a Constant Mass Ratio of w1/w2 w3

η/mPa·s

0 0.106 0.191 0.262 0.321 0.366 0.397 0.425 0.450 0.474 0.495 0.515 0.533 0.550 0.570

η/mPa·s

w3

A

w3

B 7.48 8.61 9.34 9.85 10.27 10.40 10.49 10.53 10.60 10.51 10.48 10.43 10.34 10.26 10.13

η/mPa·s

C

0 0.131 0.232 0.312 0.377 0.430 0.462 0.490 0.515

7.30 8.68 9.57 10.31 10.86 11.18 11.28 11.31 11.21

0 0.091 0.129 0.167 0.232 0.287 0.300 0.346 0.386 0.414 0.454

7.09 7.92 8.33 8.72 9.56 10.52 10.84 11.51 11.92 12.10 12.05

Figure 8. Dependence of Bi-coefficients in eq 5 on the mass fraction of IPM w1. ■, B0; ●, B1; ▲, B2; and ▼, B3. Lines are linear correlations.

relation to w1 as shown in Figure 8. The microemulsion is different from the real solution as molecules are aggregated in a droplet state. Therefore, it is not satisfactory to use the thermodynamic theoretical method to describe the behavior of the microemulsion system. In this article, just for experimental data fitting, some empirical equations were used. It can be seen from Figure 7 that, with the increase in water mass fraction w3, viscosity increases first. As the composition close to the phase separation boundary, the viscosity reaches to a maximum and then decreases. The maximum viscosity indicated a structural change from water-in-oil to a bicontinuous transition state, and then inversion, to the oil-in-water state. This phenomenon has been reported by some authors for other microemulsion systems:6−8 the bicontinuous state without a sharp boundary. Therefore, this state is existed in an indefinite region of concentration. With the increase in the content of IPM, the maximum phenomenon becomes more noticeable, and the viscosity maximum increases with the increase in w1.

mass ratio of Tween 80 to propan-1-ol is fixed at 0.5. The variation of viscosities with the mass fraction of w1 for [IPM (1) + (Tween 80 + propan-1-ol) (2)] is shown in Figure 6. An empirical equation can be used to fit the viscosity data. η /mPa·s = B0 + B1w1 + B2 w12

(4)

The parameters obtained by fitting the experimental data are given in Table 9. Figure 6 shows that the viscosity decreases with the increase in w1. For system of [(Tween 80 + propan-1-ol) (2) + water (3)], the variation of viscosity versus the mass fraction of water w3 is shown in Figure 7 . The viscosity of microemulsion phase was measured to those samples with compositions along three water dilution lines as shown in Figure 3 and as explained in the Density section. The values of viscosity at (303.15 and 313.15) K are listed in Tables 10 and 11, respectively. Viscosities have similar variation trends at the two temperatures, and the data at 303.15 K are shown in Figure 7 as an example. These viscosities can be fitted by eq 5. η /mPa·s = B0 + B1w3 + B2 w32 + B3w33

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CONCLUSION For system composed of IPM, Tween 80, propan-1-ol, and water, the microemulsion phase is a homogeneous, transparent, and stable phase. The density of microemulsion phase increases along the water dilution line. The viscosity of the microemulsion phase varies along the water dilution line shows a maximum as their composition close to the phase equilibrium boundary. This maximum is relative to the microstructure transition, that is, the microstructure transfer from water in oil (w/o) to a bicontinuous, and then inversion, to oil in water (o/w).

(5)

The parameters of eq 5 are listed in Table 12. Interestingly, the Bi-coefficients can be correlated approximately in linear

Table 12. Parameters Bi and Their Errors δBi of Equation 5, the Correlation Coefficient R, and the Standard Deviation s of the Fits Obtained by Fitting the Viscosities of Microemulsion Phases along Water Dilution Lines with Constant w1/w2 Mass Ratio w1/w2

B0

δB0

B1

δB1

0:1 0.15:0.85 0.20:0.80 0.25:0.75

8.38 7.49 7.32 7.16

0.04 0.02 0.07 0.1

28.4 10.4 8.43 1.93

1.6 0.3 1 2

0:1 0.15:0.85 0.20:0.80 0.25:0.75

7.95 7.06 6.93 6.83

0.05 0.04 0.04 0.1

27.0 3.69 3.11 −0.362

2 0.6 0.7 2.7

B2 303.15 K −175 −0.332 13.1 61.4 313.15 K −184 9.65 19.9 42.9 2028

δB2

B3

δB3

R

s

17 1 6 12

313 −17.2 −28.3 −90.9

49 1 7 18

0.9949 0.9992 0.9982 0.9959

0.04 0.02 0.07 0.13

22 2 3 13

353 −19.3 −31.1 −53.6

62 2 3 17

0.9883 0.9946 0.9975 0.9911

0.05 0.04 0.05 0.15

dx.doi.org/10.1021/je3003282 | J. Chem. Eng. Data 2012, 57, 2023−2029

Journal of Chemical & Engineering Data

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Article

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Tel.: +(86)51265880363. Fax: +(86)51265880089. Funding

This project was funded by the Priority Academic Program Development of Jiangsu Higher Education Institutions. Notes

The authors declare no competing financial interest.

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dx.doi.org/10.1021/je3003282 | J. Chem. Eng. Data 2012, 57, 2023−2029