Temperature Induced Emulsification and Demulsification of

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Temperature Induced Emulsification and Demulsification of Pseudoternary Mixtures of Tween80ButanolKeroseneWater System Partha Mukherjee,† Sandhyamayee Sahu,† Susanta Kumar Padhan,† Sukalyan Dash,‡ Sabita Patel,§ P.K. Mohapatra,|| and B.K. Mishra*,† †

Centre for Studies in Surface Science and Technology, School of Chemistry, Sambalpur University, Jyoti Vihar—768019, India Department of Chemistry, Veer Surendra Sai University of Technology, Burla—768 018, India § Department of Chemistry, National Institute of Technology, Rourkela—769008, India Radiochemistry Division, Bhaba Atomic Research Centre, Trombay, Mumbai—400 085, India

)

‡

ABSTRACT: The phase diagrams of pseudoternary mixtures of Tween80butanolkerosenewater system were constructed by visual titration. The major three domains, i.e., oil in water, bicontinuous, and water in oil microemulsions were demarcated through conductivity measurement. A sharp increase in specific conductance in increasing water content in the bicontinuous domain has been ascribed to the percolation of ions through water continuum. Temperature induced clouding behavior of the mixtures in the Winsor IV domains was investigated to find out the effect of composition on the clouding temperature. A generalized regression model was proposed considering the cloud point to be a function of surfactant/cosurfactant ratio and oil and emulsifier contents. The increase in all these parameters increases the cloud points of the mixture. In the turbid Winsor III domain, temperature has an emulsifying effect. With increase in temperature, the turbid phase separates to three different phases, which experience transparent, translucent, and turbid characteristics due to mass transfer from one phase to another. The mass transfer phenomenon was well visualized by using nickel as water-soluble and N-alkyl 4-(p-N,N-dimethylaminostyryl)pyridinium dyes as oil-soluble probes.

’ INTRODUCTION Kerosene based microemulsions have found potential applications in the various fields of industry, in the synthesis of nanomaterials, and in the determination of trace elements.15 Many heavy metals and rare earth elements were extracted either in kerosene based microemulsion system or in a solvent extraction technique using kerosene.69 For the removal of heavy crude oil fractions like asphaltenes, which inhibit fluid transportation process, a pseudoternary mixture of Unitol L 90/butanol/water/ kerosene was used successfully.10 The pseudoternary microemulsion system consisting of water/butanol/potassium oleate/ kerosene was exploited for the synthesis of nickel nanorods with a diameter 810 nm and a length 100200 nm by reducing nickel chloride with hydrazine hydrate.11 Because a microemulsion system provides microdomains with specific dimension for the substrates in chemical reactions, this characteristic is the crux in controlling the shape and size of the particles. A unified classical and molecular thermodynamic model was developed in order to predict the phase behavior and interfacial properties of spherical water-in-oil microemulsions by Peck et al.12 Considering various interactions like the surfactant tails and ionic head groups with the solvent, the interfacial tension and the bending moment of the interface were calculated explicitly. Given a surfactant molecular architecture, the model is able to predict the size of microemulsion droplets as a function of the chain length of the alkane solvent. For bis(2-ethylhexyl) sodium sulfosuccinate (AOT) in the solvents propane through decane, the calculated trends agreed well with the experimental results. The impacts of extended surfactant structure (number of polypropylene r 2011 American Chemical Society

oxide groups and branching nature of the hydrocarbon chain) on microemulsion formation for triglyceride oils and interfacial tension (IFT) values were examined, and it was found that branching of the hydrocarbon tail of extended surfactants lowers optimum salinity and IFT values.13 The important factor in the use of microemulsions in extraction methods is the heat sensitivity. With variation of temperature, nonionic surfactant systems, either micelles or microemulsions exhibit clouding behavior with distinct partitioning of surfactants between two phases. This phenomenon has also been exploited extensively for trace metal extraction and synthesis in surfactant systems.1427 The partitioning coefficient of some ethoxylated alkylphenol surfactant species between oil and water was found to vary with the oligomer characteristics (degree of ethoxylation, alkyl chain length), the phase nature (oil alkane carbon number, aqueous phase salinity), and cosurfactant (n-pentanol).28 In an investigation on the selectivity for partitioning of different probes in their mixture (one may be a drug) in Winsor type I and III microemulsion systems containing water, sodium di-n-hexyl sulfosuccinate, and NaCl, it was found that the selectivity toward the oil was high at low electrolyte concentrations.29 A simple mathematical model was developed for the selectivity, which combines the two-state solubilization theory and the net-average curvature model of microemulsion solubilization to yield close Received: December 11, 2010 Accepted: September 21, 2011 Revised: September 9, 2011 Published: September 21, 2011 11889

dx.doi.org/10.1021/ie102480d | Ind. Eng. Chem. Res. 2011, 50, 11889–11896

Industrial & Engineering Chemistry Research agreement with the experimental data. Liu et al. tried to estimate micellewater distribution of some arenes by using a simple model with geometric mean of the surface tension reductions, and the total molecular surface area of the arene in some nonionic surfactant solutions. They suggested the use of the model for the soil flushing/washing process.30 By using a simple turbidity experiment, James-Smith et al. deduced very insightful information regarding the drug and fatty acid binding capacity of microemulsions. Some Pluronic F127based oil-in-water microemulsions of various compositions were titrated to turbidity with concentrated amitriptyline, an antidepressant drug. Above certain concentrations of the surfactant, turbidity was never observed, irrespective of how much amitriptyline was added to the microemulsion. The binding of the drug with sodium caprylate as well as with the microemulsion was determined from the turbidometry study.31 As the surfactant compositions in different domains derived from the clouding behavior of microemulsions, it can be harnessed to explore extraction of various substrates. Clouding phenomenon occurs with increasing temperature, and thus, tuning of temperature is an important factor for the purpose. Herein, we made an attempt to investigate the phase behavior of mixture of Tween80, butanol, kerosene, and water with the variation of surfactant and cosurfactant ratio. The clouding behavior of the different pseudoternary microemulsion was investigated, focusing on the variation of cloud point (CP) with change in composition of different components of the microemulsion. To optimize the clouding behavior at low temperature, the effect of various additives on the clouding phenomenon was investigated. Further, the partitioning of organic as well as inorganic substrates due to clouding phenomena was also studied.

’ EXPERIMENTAL SECTION Materials. Tween80 (polyoxyethylene (20) sorbitan monooleate) was obtained from Sigma, Aldrich, and was used without further purification. n-Butanol (Merck, India) was mixed with fused CaCl2 and subsequently stirred for 48 h. It was then filtered and distilled, and pure n-butanol was collected at 116 °C. Commercially available kerosene obtained from the local market was purified by treatment with hydrochloric acid and passed through a silica gel column followed by distillation. The distillate at the temperature range 118185 °C was collected for subsequent use. Sodium chloride (AR) was obtained from Merck, India, and was dried in the oven at 110 °C for 24 h before use. Millipore water (1 μs) was used for the entire experimental study. Nickel chloride, glucose, sucrose, urea, and ammonium thiocyanate were purchased from Merck, India, and recrystallized from water twice before use. N-Butyl-p-N,N-dimethylaminostyryl pyridinium bromide and N-cetyl-p-N,N-dimethylamino styryl pyridinium bromide were synthesized by the method reported earlier.32 Phase Behavior of Pseudoternary Mixture. The phase behavior of Tween80/n-butanol/kerosene/water with different ratios of Tween80 and n-butanol (3:1, 2:1, 1:1, and 1:2) systems was investigated, principally focusing on the identification of single-phase regions. The change in phases was determined at 30 °C by taking calculated amounts of Tween-80 and n-butanol and different amounts of kerosene in PTFE-faced screw-cap Pyrex tubes. The samples were successively titrated with Millipore water while stirring with Teflon coated magnetic bar for homogeneous mixing. The amount of water forming a clear zone and a turbid zone were noted, and three-dimensional phase diagrams were

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constructed by considering mass ratios of the components. Surfactants and cosurfactant are considered as a pseudocomponent (Emulsifier, E), with the other variables being water (W) and kerosene (O). Phase diagrams of Tween80/n-butanol/kerosene were constructed with 2% brine to examine the effect of brine on the phase behavior of this quaternary system. CP Measurements. CPs of the microemulsions with varying composition were determined visually by placing the microemulsion sample solution in a pyrex glass tube and keeping it in a thermostatted water bath raising its temperature to 1 °C/min. The temperature at the appearance of cloud was recorded. Further, from the elevated temperature, the system was cooled down to a transparent medium, and the transition temperature was noted. The mean of these two temperatures was considered as the CP of the system. In the similar method, the CP of the microemulsion in presence of 2% brine and other additives like glucose, sucrose, urea, and ammonium thiocyanate was determined. The values determined are the mean of three separate determinations with an error less than (0.5 °C. Electrical Conductivity Measurements. To demarcate the oil-in-water and water-in-oil domain in the isotropic zone of the ternary mixture in the phase diagram, conductivity measurements of the microemulsions with brine as the substitute for water were conducted at 30 °C using Systronics 304 direct reading conductivity-meter standardized with N/10 KCl solution at an automatically controlled frequency within a range 0.11.0 kHz. Determination of Partitioning of Different Substrates. A solution of the substrate in water or butanol was introduced while preparing a microemulsion replacing water or butanol, respectively, in accordance with their solubility. On heating above the CP in thermostatted water bath, clouding occurred leading to phase separation. Partitioning was determined by measuring the absorbance of the different substrates in microemulsion before CP and again measuring the absorbance of substrates after phase separation due to clouding by using a Hitachi U-3010 UVvis spectrophotometer.

’ RESULTS AND DISCUSSION Phase Behavior. The pseudoternary phase diagram of emulsifier (E) (surfactant (S) Tween 80 + cosurfactant (C) butanol (S/C = 1)), oil (kerosene (O)), and water (W) system obtained at constant temperature and pressure is presented in Figure 1a. The Winsor IV domain covers almost the E apex covering an area of 42.5% of the total area of the phase diagram. A narrow band touching the W apex indicates the formation of micelles of Tween-80 and water solubilizing a small amount of kerosene and butanol. With increase in emulsifier, the transparent band broadened with microheterogeneous assemblies with a greater amount of kerosene dissolved in water rich systems. In the oil rich domain, transparent microemulsions could be established above 30% of emulsifier. Just above this weight fraction of emulsifier a turbid island was obtained in the transparent domain. Increase of cosurfactant to twice of the surfactant resulted in significant decrease up to 13.5% in the Winsor IV domain (Figure 1d). A tiny isotropic island in the turbid zone touching the W apex indicates the existence of micelles wherein some kerosene is soluble. Within this domain the amount of kerosene did not exceed 2%. Further, no turbid island was observed in the Winsor IV domain. With decrease in cosurfactant amount in the emulsifier, the Winsor IV domain decreases, however, not appreciably (Table 1). 11890

dx.doi.org/10.1021/ie102480d |Ind. Eng. Chem. Res. 2011, 50, 11889–11896

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Figure 1. Phase diagram of pseudoternary mixture of Tween80 (S) and butanol (C) as emulsifier (E), kerosene (O), and water (W): S/C = (a) 0.5, (b) 1, (c) 2, (d) 3.

Table 1. Isotropic Domain of Tween80/n-Butanol/Kerosene/Water System with the Variation of Surfactant Cosurfactant Ratio surfactant:cosurfactant

% isotropic domain

1:2

13.5

1:1 2:1

42.5 37.5

3:1

36.25

1:1(with 2% NaCl)

29.25

Addition of sodium chloride squeezed the Winsor IV domain. At 1:1 volume ratio of surfactant and cosurfactant, addition of 2% of sodium chloride could decrease the isotropic domain from 42.5% to 29.25% all projecting toward E apex (Figure 2). As sodium chloride is inert to the other constituent like Tween-80, butanol, and kerosene, the change in the morphology of the mixture is mostly contributed by the water structure, which is highly sensitive toward sodium chloride. The asymmetric nature of the phase behavior of the quaternary mixture added some more characteristics with change in composition. At 2:1 (Figure 1b) volume ratio of surfactant and cosurfactant, no island was observed in the Winsor IV domain; however, there appeared a small isotropic turbid indentation parallel to the EO edge. With further decrease of cosurfactant (Figure 1c), a narrow transparent zone paved its way into the

Figure 2. Phase diagram of pseudoternary mixture of Tween80 (S) and butanol (C) as emulsifier (E), kerosene (O), and brine (W): S/C = 2; brine 2% NaCl solution.

turbid phase toward O apex. In this oil rich domain, water can be solubilized to 510 wt %, possibly forming swollen reversed micelles. A large turbid gel domain was also observed at lower amount of emulsifier extending toward O apex. Addition of sodium chloride induced more asymmetric characteristics to the phase behavior of the quaternary mixture (brine in place of water). Kabalnov et al. have observed different microstructures: discrete water or oil droplets and bicontinuous, 11891



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Table 2. Variation of CP with Microemulsion Composition CP in oC E:O:W ratio

Figure 3. Representative plot of specific conductance vs volume of NaCl.

depending, inter alia, on the surfactant polarity, salinity, temperature, and cosurfactant.33 The decrease in Winsor IV domain was also accompanied by the appearance of a large turbid island in the emulsifier rich region close to EW edge and another small turbid island close to EO edge around 50% weight percent of emulsifier (Figure 2). A small water rich micellar phase within 20% of emulsifier contents appeared in the phase diagram. This micellar phase can solubilize kerosene up to 4% weight percent. The Winsor IV domain is a mixture of some complex heterogeneous systems, aggregates of surfactants, cosurfactants, water, and kerosene at various compositions. In these complex systems the uneven distribution of surfactants and cosurfactants in each aggregate cannot be ruled out. To make an attempt at identifying various microheterogeneous domains, conductometric analysis of the isotropic domain was carried out by replacing water by 2% sodium chloride solution. The plots of specific conductance versus volume percent of brine (Figure 3) are found to be sigmoidal type showing two distinct transitions separating three different domains. The initial slow increase upon increase in brine is assumed to be the conductivity in oil rich phase with increasing dispersed water droplets in the system, which may be ascribed to a water in oil (W/O) microemulsion. The subsequent sharp increase in the conductivity with increase in water content may be ascribed to the percolation of ions in the bicontinuous (BC) phase, where both oil and water provide channels for transportation of nonpolar as well as polar solutes. A subsequent change in the increasing trend of specific conductance with increase in the amount of water may be due to the water continuum having dispersed oil droplets, i.e., an oil in water (O/W) microemulsion. From the transition points of the plots of specific conductance and water/hexane contents, the three domains of O/W, BC, and W/O are demarcated in the phase diagram (Figure 1a). Effect of Composition of Microemulsion on CP. The CPs of the pseudoternary mixture of emulsifier, water, and oil varied between 36 to 78 °C with change in composition (Table 2). However, with a fixed ratio of S/C the CP did not vary significantly. The analysis of the data of Table 2 reveals the following. (1) With constant emulsifier, in all the three compositions of emulsifier (S/C = 1, 2, and 3), CP increases with increase in oil content. (2) With decrease in cosurfactant composition in emulsifier, CP increases significantly. (3) With constant water contents and decrease in oil content, CP increases.

S/ C = 1

S/ C = 2

S/ C = 3

50:5:45

36

57

66

50:15:35

38

60

50:20:30

40

66

50:30:20

41.5

55:20:25

42

60:20:20

45

35:5:60

36

54.5

45:20:35 40:10:50

39

62 57.5

78.5

(4) With constant oil contents and decrease in water content, CP increases. Among the constituents of the mixture, Tween80 is the selfaggregating species, which is responsible for the formation of different aggregates in the mixture of both oil and water. Aggregation destabilizes due to unsymmetrical distribution of both water and oil resulting in demulsification. On heating process, mass transfer takes place among the microheterogeneous aggregates, and thus, relative dehydration of an aggregate may lead to destabilization of the aggregation, which is observed by clouding phenomenon. Prediction of CP with the variation of composition in Tween 80/kerosene/butanol/water pseudoternary microemulsions could be achieved with the aid of regression analysis of the experimental data. It was found that there is very good agreement of predicted CP with that of observed CP for each specific ratio of S/C (eqs 1 for S/C = 1 and eq 2 for S/C = 2). CP ¼ ð30 ( 2Þ þ ð0:0048 ( 0:0023ÞO2 þ ð0:0030 ( 0:0009ÞE2 R 2 ¼ 0:98, F ¼ 68:20, N ¼ 8

ð1Þ CP ¼ ð51 ( 2Þ þ ð0:019 ( 0:0012ÞO2 þ ð0:0022 ( 0:0013ÞE2 R2 ¼ 0:97, F ¼ 71:43, N ¼ 7

ð2Þ 2

O and E refer to weight percent of oil and emulsifier, and R , F, and N are statistical parameters like regression coefficient, F-test, and number of data points, respectively To have a generalized model an attempt was made to formulate a universal equation to predict the CP for all ratios of surfactant and cosurfactant of the Tween 80/kerosene/ butanol/water pseudoternary system (eq 3). CP ¼ ð6 ( 4Þ þ ð23:34 ( 1:38ÞS=C þ ð0:012 ( 0:002ÞO2 þ ð0:0025 ( 0:001ÞE2 R ¼ 0:97, F ¼ 105:91, N ¼ 15

ð3Þ

2

It is observed that all the variables have positive contribution toward CP. By using the above regression models, the CPs are calculated, and the plots of observed and predicted CPs are given in Figure 4. Effect of Various Additives on CP. Additives play an important role to tune the CP of the microemulsion system to the desired range to facilitate the extraction of various compounds 11892



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Figure 4. Plot of predicted CP vs observed CP values of all the microemulsion systems considering (a) eq 1, (b) eq 2, and (c) eq 3.

Table 3. Effect of Various Additives on CP for S/C = 1 2%

2%

2%

2%

2%

H2O

brine

NH4SCN

glucose

urea

sucrose

50:5:45

36

27

42

33.5

34.5

50:15:35

38

30

45

35

50:20:30

40

32

48

37

38.5

50:30:20

41.5

33.5

41.5

47.5

55:20:25

42

60:20:20

45

35:5:60

36

45:20:35

39

E:O:W ratio

Table 4. Effect of Brine on CP for S/C = 2 E:O:W ratio

H2O

2% brine

29.5

50:5:45 50:20:30

57 66

46 51

31.5

50:30:20

33

45:20:35

62

49.5

38.5

60:20:20

no clouding up to 84

56

54

using CP technology. CP of Tween 80/kerosene/butanol/water pseudoternary system with S/C = 1 was investigated in the presence of various additives such as salts, sugars, and nonelectrolytes (table 3). A depression of CP was observed with the addition of NaCl in the quaternary system. The depression was more pronounced in the pseudoternary system with the increase in surfactant in emulsifier (Table 4). At a high emulsifier content with S/C = 2, where clouding could not be observed, even at 86 °C, in the presence of NaCl, clouding was obtained at 56 °C. This depression in CP may be ascribed to the salting out effect by NaCl. Al-Ghamdi and Nasr-El-Din observed similar depression in CP in Triton-X nonionic surfactant solutions by NaCl.34 However, an increase of CP was manifested with the addition of NH4SCN. The elevation of CP may be attributed to the salting in effect of the lyotropic salt, NH4SCN. The addition of sugars like glucose and sucrose in the quaternary system led to slight depression in CP. The effect seems to be nullified as one proceeds from water rich region to oil rich region. Nonelectrolyte urea manifested an interesting impact on the CP: in the water rich region a slight depression was observed whereas an elevation of CP was observed in the oil rich region. Urea is believed to be a structure breaker and is found to increase the CP values of nonionic surfactants.35 For increasing CP, two mechanisms for urea action on micellar solutions have been proposed. Urea changes the structure of water to facilitate the solvation of a hydrocarbon chain, and hence, there is an elevation of CP. Further urea replaces several water molecules that solvate the hydrophobic chain and the polar headgroup of the amphiphile. Urea as a water structure breaker is well established.36 Kumar et al. have also observed that the CP of aqueous TX-100 solutions decreases at low concentration of urea while with high concentration CP increases.37 They have attributed this observation to

56

the influence of urea on aggregational properties of aqueous surfactant systems. Temperature Induced Three-Phase Behavior. Temperature induced three-phase behavior was observed in the Winsor III domain of the Tween80butanolkerosenewater pseudoternary system. The pseudoternary mixtures of the marked domain in Figure 5 assume single turbid phase, which undergoes phase separation on raising the temperature of the medium. The following observations were made with increase in temperature from the room temperature (27 °C) at a rate of 0.2 °C min1. (1) Around 37 °C the single turbid pseudoternary mixture was separated into two turbid phases: upper oil rich phase and lower water rich phase. (2) When temperature was raised to 42 °C, the upper oil rich phase became translucent and finally transparent, while the lower phase remained turbid. (3) At around 51 °C a cloud was appeared in the lower phase, which became completely cloudy at around 56 °C. (4) On further increase in temperature to 59 °C, a third phase started developing with the appearance of transparent region at the bottom of the container. Up to 66 °C the domain of the third phase increased to its maximum, and on further heating up to 78 °C no change in the volume of the three phases was observed. However, at this temperature upper phase was found to be transparent, middle phase to be turbid, and lower phase to be translucent. (5) With the decrease in temperature the middle turbid phase turned to completely transparent at 67 °C. The three clear phases coexisted at this temperature (Figure 4a). (6) Further decrease in temperature to 50 °C, a turbid ring appeared at the interface of middle and lower phases. The lower phase turned turbid, while the other two phases remained transparent. The turbid ring was widened to form a semisolid turbid band on standing the three phase body for a day. The turbid semisolid band remained stable for a month, and it was stuck with the container. 11893



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Table 5. Partitioning of Different Substrates due to Clouding of the Microemulsion at the Composition E:O:W = 50:5:45 (Weight Percent) Kd analytical substrate

wavelength in nm

1:1

2:1

3:1

N-butyl-p-N,N-dimethyl amino styryl

473

0.59 0.74

480

0.43 0.62 0.71

395

2.26 1.17 1.12

pyridinium bromide N-cetyl-p-N,N-dimethyl amino styryl pyridinium bromide Ni2+

Figure 5. (a) Three phase separation of the turbid pseudoternary mixture, and (b) phase diagram representing mass transfer in three phase separation.

The above observations lead to the following inferences. (1) The pseudoternary mixture of the experimental composition assumes a combination of different microheterogeneous phases like oil, water, micellar medium, microemulsions, etc. (2) Initially with the rise in temperature, the upper turbid phase, rich in kerosene, becomes transparent due to mass transfer from the upper phase to the lower phase. (3) Further, with increase in temperature, a micellar phase separates out at the bottom with smaller amounts of surfactants and cosurfactants compared to the middle phase and a trace amount of oil in it. (4) The middle phase experiences a transition from emulsion to microemulsion phase with mass transfer between this phase and both upper and lower phases. Initial turbidity at 66 °C is due to clouding phenomenon of the microemulsion. (5) With time, at room temperature, mass transfer takes place between the phases, and a stable gel is formed in the surfactant rich middle phase. A similar phenomenon has been observed by other workers during the study of salt effect on phase separation behavior of microemulsions.38,39 However, they have observed the formation of three phases above 100 °C induced by the addition of salt and have explained the phenomenon on the basis of salting in and salting out mechanism. In the present investigation, the three-phase separation may be due to differential solubility of the emulsifier in oil-rich and waterrich regions with different temperature conditions. The initial solubilization of the emulsifier in a mixture of water and oil at a definite proportion changes with temperature. At higher temperature, water with some emulsifier separates as a micellar component and remains at the bottom due to higher density, excess oil with lower density occupies the upper region, and the microemulsion system containing all the four components having density lower than micellar system and higher than oil maintains at the middle region. The middle phase has a bicontinuous structure of microemulsion, wherein the oil-in-water microemulsion constitutes the lower side and the upper side of this phase contains water-in-oil microemulsions. Temperature had a direct impact on the density of solutions. Hence, transference of emulsifier occurs with change in temperature resulting in the change in density of various phases as well as their homogeneity. However, the upper phase always remained clear indicating the transference of the emulsifier being limited only to the middle and lower phases.

Partitioning of Different Substrates due to Clouding. Partitioning of different organic and inorganic substrates was attempted during the clouding phenomena of the mixture of Tween80kerosenebutanolwater. Further, the effect of ratio of surfactant and cosurfactant in the preconcentration of the solutes was investigated with the variation of their ratio in the pseudoternary mixture. The partition coefficient, Kd, was determined from the ratio of the amount present in the cloud and the amount present in the transparent medium. From the absorbance of the transparent medium at the analytical wavelength, the amount of the solute was determined. Due to relatively high extinction coefficient of Ni from among the other transition metals, it was considered as an inorganic probe to study its preconcentration in the microemulsion (Table 5). The transference of Ni from the transparent microemulsion medium to the emulsifier rich cloud was found to be more at low surfactant content than the higher surfactant content. It indicates that the role of oxyethylene group for entrapment of Ni is not the only criterion. Tondre and Derouiche also reported the transfer of Ni2+ through the microemulsion interface due to the contribution of oxyethylene groups.40 Further, when N-butyl 4-(p-N,N-dimethylaminostyryl)pyridinium bromide, an ionic chromophore, was taken as a probe to see its preconcentration, it was found that the partition to cloud from the transparent medium is less, but with increasing surfactant content, the Kd value increases (Table 5). When the butyl chain was replaced by a hexadecyl group, the hydrophobicity of the chromophore increases and the partitioning to the cloud was less. These observations indicate that the clouding is due to segregation of surfactants only, having no butanol or oil inside. The partitioning of the substrates is due to the entrapment of the substrates mostly though the interactions of the oxyethylene units of the surfactants.

’ CONCLUSIONS The phase diagrams constructed for pseudoternary mixtures of Tweenbutanolkerosenewater are found to be unsymmetrical. With increase in surfactant/cosurfactant ratio, the transparent microemulsion domain decreases with increased population of other aggregates. From the conductivity data the oil rich and water rich microemulsions can be demarcated. The middle domain with almost equal water and oil forms a bicontinuous phase, where organic and inorganic solutes can percolate. The pseudoternary mixture can undergo temperature induced emulsification and demulsification. The transparent medium can form cloud at elevated temperature. The CPs of the different mixtures are found to have good correlation with the composition of the mixture. Further, the turbid mixture can undergo phase separation 11894


Industrial & Engineering Chemistry Research with increase in temperature due to mass transfer from one phase to other phases. Solutes can be transferred from one phase to another through this emulsification and demulsification phenomena.

’ AUTHOR INFORMATION Corresponding Author

*E-mail: [email protected].

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