Article pubs.acs.org/EF
Influence of Ionic Liquids on the Viscoelastic Properties of Crude Oil Emulsions Douglas Alves,† Everton Lourenço,† Elton Franceschi,† Alexandre F. Santos,‡ César Costapinto Santana,† Gustavo Borges,† and Claudio Dariva*,† †
Núcleo de Estudos em Sistemas Coloidais (NUESC), Instituto de Tecnologia e Pesquisa (ITP), Pós-graduaçaõ em Engenharia de Processos (PEP), Pós-graduaçaõ em Biotecnologia Industrial (PBI), Universidade Tiradentes (UNIT), Avenida Murilo Dantas 300, Aracaju, Sergipe 49032-490, Brazil ‡ Departamento de Engenharia Química (DEQ), Universidade Federal do Paraná (UFPR), Centro Politécnico, Curitiba, Paraná 81531-980, Brazil ABSTRACT: Thermochemical treatments are traditionally employed to perform the separation between the oil and water phases in the petroleum industry. The chemical agents have the function of reducing the barrier rigidity formed by natural surfactants present in the emulsion, thus favoring destabilization. The main objective of this study was to analyze the viscoelastic properties of samples composed of water and a crude oil with the addition of distinct ionic liquids. The methodology used to obtain the interfacial properties was the pedant drop technique. The results showed that the addition of the ionic liquids induced a reduction in the interfacial elasticity and an increase in the compressibility of interfacial films. It was also observed that an enhancement in the alkyl chain length has a positive effect on changing the interfacial properties. The ionic liquid with the highest alkyl chain length investigated ([C12min]+[NTf2]−) showed the ability to produce the more elastic films for the crude oil investigated. oil phase separation process. Works of Lucero-Guzman et al.14 and Silva et al.15 showed the efficiency of the thermochemical method using IL as a surfactant and distinct types of heating. Silva et al.15 also showed that the addition of ILs significantly reduces the interfacial tension in a crude oil/water system, a crucial characteristic for a demulsifier surfactant. As previously mentioned, because these chemical species adsorbed at the interface, they have the ability to modify the characteristics of the interface and can facilitate the phase separation process. The action of these surfactants can be assessed through the interfacial properties of the water/oil interface, providing important information about the mechanism and kinetics of the migration to the interface and the viscoelastic characteristics of the interfacial film after the adsorption.16,17 Some studies in the literature show that both foam and emulsion stability can be correlated with the dilatational moduli and compressibility.18,19 Moreover, the action of natural surfactants or demulsifiers at the interface can be studied by these properties, which will provide important information about the emulsion stability.20 An adequate technique employed for the interfacial property study is the pendant drop tensiometry, where the properties are obtained through the digitalization of the liquid drop profile suspended in an another immiscible phase in dynamic equilibrium.21 The focus of this work is to investigate the effect of the addition of ILs on the interfacial properties (elasticity and compressibility) of a Brazilian oil and also analyzing the changes in the elastic and viscous characteristics of the interface
1. INTRODUCTION The presence of water in the crude oil production/processing is a great challenge faced by the petroleum industry.1 Emulsions are formed as a result of the intensive shear during the production stage and the presence of chemical surfactants naturally present in the oil.2,3 These chemical species adsorb at the interface, creating a rigid viscoelastic barrier that prevents coalescence between the droplets, enhancing the separation between oil and water phases.4,5 Demulsification steps are needed in the primary processing of the crude oil to minimize problems associated with the presence of oil emulsions.6 A variety of methods are used for this purpose in the oil industry, in combination or separately, such as gravity separation, membrane separation, filtration, electrostatic treatment, and most frequently, the thermochemical treatment, where heating of the mixture is combined with the addition of chemical demulsifier agents.7 These chemical species adsorb at the water/oil interface, promoting changes in the viscoelastic characteristics of the interfacial film.8 The modification in the interfacial properties, such as compressibility and elasticity, can favor a decrease in the rigidity of the interfacial film and, consequently, facilitate coalescence between the droplets and the demulsification process.9−12 Ionic liquids (ILs) are salts that are common in the liquid state at room temperature and are composed of organic cations associated with organic or inorganic anions. Considering their intrinsic characteristics, such as lower vapor pressure, thermal stability, and nonflammability, they are considered as “green surfactants”.13−15 Another point to be stressed about the ILs is that their amphiphilic characteristics can be modulated by an appropriate selection of cations and anions.15 Some authors investigated the efficiency of ILs as a demulsifier in the water/ © 2017 American Chemical Society
Received: May 16, 2017 Revised: August 14, 2017 Published: August 14, 2017 9132
DOI: 10.1021/acs.energyfuels.7b01418 Energy Fuels 2017, 31, 9132−9139
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laser diffraction technique (Mastersizer 2000, Malvern). In the emulsification process, a homogenizer system was used (Ultra Turrax T25 Basic, IKA) at 9500 rpm to obtain water-in-oil emulsions with a small dispersion droplet size distribution in the range of 9−11 μm. After the emulsion synthesis, the samples were inserted in 100 mL graduated tubes, where it was possible to visually monitor the phase separation. Finally, for the demulsification process, the tubes containing the emulsions were placed in a thermal bath at a temperature of 80 °C. 2.3. Interfacial Properties. The interfacial properties were obtained at room temperature using a pedant drop tensiometer (Teclis Tracker, IT Concept). The oil sample was inserted into a syringe having a U-shaped needle. The needle was then immersed in the glass cell containing the aqueous phase to produce a single drop of oil. A charge-coupled device (CCD) camera captured the drop shape, and the interfacial tension was assessed by the Young−Laplace equation resolution.23 Three methods were employed to determine the interfacial properties: static measures of the drop shape to obtain the interfacial tension values, oscillatory tests from sinusoidal perturbations of the interfacial area to assess the interfacial elasticity and its components, and compression tests where the inverse of compressibility is measured by drop compression at a constant rate. To determine the interfacial tension measurements, interfacial elasticity, and compressibility, it is necessary to perform the previous selection of volume and drop area, amplitude, and frequency of oscillation. The volume used in the experiments directly affects the noise of interfacial tension measurements, also affecting the elasticity interfacial and compressibility measures. Thus, an optimal volume should be chosen to produce a low noise and to avoid a drop detachment on the needle for long aging times. The amplitude is chosen by analyzing the region where the elasticity values are constant for different amplitude values. 2.3.1. Dilatational Elasticity. A more detailed description of the dynamic interfacial measurements can be found in a previous work of our group.22 Briefly, in this work, the oscillatory tests were made with a frequency of 0.1 Hz. This frequency produces a reduction in the surfactant self-reorganization effect.4,23,24 The interfacial elasticity values were determined by controlled oscillations of the interfacial area of the drop, with predetermined frequency and amplitude. These disturbances in the interface area cause an equivalent response of the interfacial tension. The interfacial elasticity (ε) is the ratio between the variation of the interfacial tension and drop area19,21,25
when these surfactants are inserted into the crude oil multicomponent system. To achieve these goals, the interfacial properties were determined for systems involving a Brazilian crude oil by adding distinct concentrations and structure types of ILs. The interfacial properties were obtained through static and dynamic tests in the pedant drop technique and provide information about the elasticity and compressibility of the interfacial film of the analyzed systems. Stability tests were also performed to provide a clear relationship between the stability emulsions containing the ILs and the interfacial properties.
2. MATERIALS AND METHODS 2.1. Materials. The crude oil used in this work has the characteristics presented in Table 1. The characterization was performed according to standard methods at the Petrobras Research and Development Center and in our lab.22
Table 1. Characteristics of the Brazilian Petroleum Used in the Work property
value
methodology
density (API gravity, deg) viscosity at 40 °C (cP) water and sediments (%, v/v) TAN (mg of KOH/g) SARA analysis (wt %) saturates aromatics resins asphaltenes
28.4 24.6 0.8 0.36
ASTM ASTM ASTM ASTM ASTM
D5002 D7042 D4007 D0664 D6560
52.6 27.2 19.9 0.33
ILs tested in this work were purchased from Ionic Liquids Technologies, Inc. (IOLITEC, Germany) and were used as received. Besides a distinct concentration of ILs, the effect of the cation alkyl chain length was evaluated on the water/oil interfacial properties. The ILs investigated were 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide [C4min]+[NTf2]−, 1-methyl-3-octylimidazolium bis(trifluoromethylsulfonyl)imide [C8min]+[NTf2]−, and 1-dodecyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide [C12min]+[NTf2]−. 2.2. Sample Preparation. Two phases are required for the tensiometry experiments. In the aqueous phase, ultrapure water was used. In the second phase, the crude oil was used with the addition of ILs, which were homogenized by magnetic stirring. For the synthesis of samples with the IL [C12min]+[NTf2]− (greater cationic chain length), this surfactant was diluted in crude oil in different concentrations of 5, 15, 30, 50, 75, 100, and 125 ppm, and for the other ILs, interfacial properties were evaluated at a fixed concentration of 100 ppm. The emulsions used in the stability tests were synthesized with the ILs at the concentration of 100 ppm. All of the emulsion preparation was performed according to the methodology available in the literature and extensively used by our group.22 The samples were characterized in terms of the water content (WC) by the Karl Fischer reagent titration (model 836 Titrando, Metrohm) and set at 45 wt % (Table 2). The droplet size distribution (DSD) was determined by the
ε=
[C4min]+[NTf2]− [C8min]+[NTf2]− [C12min]+[NTf2]−
D[4,3] (μm) 10.2 10.0 10.3 10.2
± ± ± ±
0.3 0.2 0.2 0.5
ε = ε′ + ε″i
± ± ± ±
(2)
These properties depend upon the phase angle (ϕ) between the variations in the interfacial tension and interfacial area. Thus, the phase angle shows if the interfacial film has elastic (near 0°) or viscous characteristics (away from 0°)19 ε′ = |ε|cos ϕ
(3)
and ε″ = |ε|sin ϕ
(4)
These properties were measured at intervals of 1 h for a total time of 24 h. After this time, the influence of different oscillation frequency values was analyzed in the interfacial elasticity measures in a well-aged interface. The experiments were performed with the frequencies of 0.02, 0.05, 0.0667, 0.14, 0.2, and 0.5 Hz. 2.3.2. Compressibility. The compressibility measurements were made by compression of the drop interfacial area from a constant rate for a predetermined aging time. The values of compressibility for different aging times are determined by the equation26
WC (wt %) 44.6 46.0 44.3 46.0
(1)
where y is the interfacial tension response and A is the droplet area. The interfacial elasticity has a real component (ε′, elastic modulus) and another imaginary component (ε″, viscous modulus).
Table 2. Characterization Values of the Emulsions Synthesized in Terms of the WC and Average Droplet Size by Volume D[4,3] for the Samples with Distinct ILs IL
dy d ln A
0.6 2.0 0.5 2.0 9133
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Figure 1. Interfacial tension (γ) at room temperature between the crude oil and water as a function of the concentration of the IL [C12min]+[NTf2]− in the crude oil after 90 min.
Figure 2. Interfacial tension (γ) at room temperature as a function of time for ILs with a distinct alkyl chain length at a fixed concentration of 100 ppm in the crude oil.
c=
d ln A′ dπ
surfactant leads to a lowering of the interfacial tension, being well correlated with the destabilization of emulsions. Results from the literature15 pointed out that the reduction in the interfacial tension was smaller for the ILs [C4min]+[NTf2]− and [C8min]+[NTf2]−. Therefore, because the value of 100 ppm has shown the lowest value of interfacial tension for [C12min]+[NTf2]− (seen in Figure 1), this concentration was chosen to highlight the interfacial tension reduction for the surfactants with a lower alkyl chain length and make a safe comparison to [C12min]+[NTf2]− and original crude oil (without surfactant). Figure 2 shows the interfacial tension dynamics of different alkyl chain lengths over time. Silva et al.15 studied the separation efficiency of a heavy crude oil emulsion using the same ILs tested in this work. Interfacial tension measurements were carried out, and a similar behavior of that shown in Figure 2 was observed. The addition of ILs [C4min]+[NTf2]− and [C8min]+[NTf2]− showed an slight decrease in the interfacial tension compared to the crude oil (free of IL). Figure 2 also provided evidence that the addition of the [C12min]+[NTf2]− IL at the same concentration showed a considerable reduction in interfacial tension compared to other ILs. This behavior can be attributed to the fact that IL with higher alkyl chains has a greater tendency to migrate to the
(5)
where A′ and π are the decrease of the area and the interfacial tension during the compression, respectively. In this work, the inverse of compressibility values will be presented, in which the magnitude is determined by the tangent of the curve produced from the A′ and π values. The compression rates used were equivalent to the frequency of 0.1 Hz, and the aging times were 30 min and 2, 4, and 16 h.
3. RESULTS AND DISCUSSION 3.1. Interfacial Tension. Initially static tests were performed to determine the interfacial tension of samples with different concentrations of [C12min]+[NTf2]− diluted in the crude oil. The results are shown in Figure 1 for an aging time of 90 min. The addition of the IL provides a continuous decrease in the interfacial tension compared to crude oil (0 ppm) up to 100 ppm, when the interfacial tension seems to achieve a plateau in relation to the IL concentration. This decrease in the interfacial tension observed in this study is consistent with the works of Pradilla et al.27 and Xu et al.,9 who analyzed the interfacial tension of regular demulsifiers and found that the addition of a 9134
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Figure 3. (a) Interfacial elasticity (ε) as a function of time in systems of crude oil with the addition of different concentrations of the IL [C12min]+[NTf2]−. (b) Elastic (ε′) and viscous (ε″) components as a function of time in systems of crude oil with the addition of different concentrations of the IL [C12min]+[NTf2]−.
less rigid formation of water/oil films. The difference is less significant in the first hour, but it increased with the aging time of the interfacial film, suggesting an intense interfacial activity during the initial phase of the test. The behavior of the elastic and viscous components seen in Figure 3b shows that there is an evident reduction in these properties with the addition of ILs, corroborating with the results of Figure 3a. Still in Figure 3b, it can be seen that all viscous modulus values are much smaller than the elastic modulus values. Even more, it is possible to see from Figure 3b that the addition of the IL significantly reduces the viscous modulus of the investigated system, thereby forming an interface with a further elastic characteristic of the crude oil film (0 ppm). This behavior can be evidenced in Table 3, which contains values of the phase angle for the investigated systems. According to Table 3, it is seen that the addition of 50 ppm of [C12min]+[NTf2]− causes the phase angle to decrease around 50% of its original value in the crude oil. Because the viscous modulus depends upon the sine of the phase angle (eq 4), the reduction of the phase angle results in a reduction at the
interface, shifting the natural surfactants of the crude oil. This effect shows the ability of the surfactant to migrate to the interface and the performance to destabilize the crude oil emulsion.11 3.2. Dilatational Elasticity. The effect of the concentration of the [C12min]+[NTf2]− IL on the dilatational moduli (ε, ε′, and ε″) was investigated through dynamic oscillatory tests. The concentration of 100 ppm was used for the IL diluted in the crude oil. The results are presented in panels a and b of Figure 3. Figure 3a shows that, for 5 ppm of IL [C12min]+[NTf2]−, the values of the total viscoelastic modulus were close to the crude oil system (0 ppm). Because an appreciable reduction in interfacial tension to this concentration was not checked, a small change in the rigidity of the interfacial film was expected. These results show a good correlation between the values of interfacial tension and elasticity for this concentration. On the other hand, for the concentrations of 50 and 100 ppm of IL, the reduction in the overall modulus values suggests the destabilizing action of the tensoative species, indicating the 9135
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modulus. In Figure 4a, the increase in the alkyl chain length of IL leads to a reduction of the analyzed properties, consistent with the results of interfacial tension (Figure 2). The enhancement in the alkyl chain length of IL promotes the migration of tensoative species to the interface, reflecting the reduction of the viscoelastic properties. As a consequence, less rigid film is formed, suggesting a more favorable destabilization when ILs of higher alkyl chain length are added to the oil sample. In Figure 4b, it can observed that the crude oil sample of IL with a higher alkyl chain length ([C12min]+[NTf2]−) has a greater ability to alter the viscoelastic characteristic of the interfacial film formed. The considerable reduction of the viscous modulus makes the film more elastic than the system without IL in the crude oil. However, the samples of other ILs did not show a significant reduction of the viscous modulus. The emulsion separation tests performed by Silva et al.15 with the addition of the ILs demonstrated that the alkyl chain length of IL significantly favored the separation between phases. The authors reported that the use of ILs [C8min]+[NTf2]− and [C12min]+[NTf2]− resulted in higher efficiencies of demulsifi-
Table 3. Phase Angle Values Measured in Oscillatory Tests for the IL [C12min]+[NTf2]− Added to the Crude Oil at Room Temperature concentration (ppm)
phase angle (deg)
0 50 100
14.6 ± 1.0 7.5 ± 1.8 7.2 ± 0.8
value of this component as well (Figure 3b). This information indicates a modification in the characteristic of the interfacial film formed from the addition of the IL in the oil phase. Another factor to be noted is that the reduction of the viscous modulus, resulting in the change in the interfacial film characteristics, is independent of the aging time, which is consistent with the work of Yarranton et al.19 Panels a and b of Figure 4 show the results of the total viscoelastic modulus and its components for the system containing crude oil with the addition of different alkyl chain length ILs at 100 ppm. Through panels a and b of Figure 4, it can be observed that the addition of ILs considerably reduces the viscoelastic
Figure 4. (a) Interfacial elasticity (ε) as a function of time in systems of crude oil with the addition of ILs at a concentration of 100 ppm. (b) Elastic (ε′) and viscous (ε″) components as a function of time in systems of crude oil with the addition of ILs at a concentration of 100 ppm. 9136
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Figure 5. Influence of the oscillation frequency on the interfacial elasticity (ε) in systems of crude oil with different [C12min]+[NTf2]− concentrations.
Figure 6. Influence of the oscillation frequency on the interfacial elasticity (ε) in systems of crude oil with different ILs at the same concentration (100 ppm).
Figure 7. Inverse of compressibility (c−1) as a function of time for systems of crude oil with the addition of different concentrations of the IL [C12min]+[NTf2]−.
and b of Figure 3 and panels a and b of Figure 4 with an aging time of 24 h and different values of oscillatory frequencies. These results are presented in Figures 5 and 6. It can be observed in Figures 5 and 6 that the oscillation frequency has a positive effect in the dilatational elasticity, being
cation, reaching values of 74 and 90%, respectively. Thus, these results indicate that increasing the alkyl chain length leads to the creation of a less rigid interfacial films with a less stable emulsion. Still in oscillatory tests, measurements of dilatational elasticity were taken for the same systems presented in panels a 9137
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Figure 8. Inverse of compressibility (c−1) as a function of time for systems of crude oil with the addition of ILs at a concentration of 100 ppm.
Figure 9. Stability tests for water-in-oil emulsions containing the ILs [C4min]+[NTf2]−, [C8min]+[NTf2]−, and [C12min]+[NTf2]− at a concentration of 100 ppm and crude oil.
in accordance with the work of Yarraton et al.,19 Alves et al.,23 Sztukowski and Yarraton,24 and Dicharry at al.28 The main information observed in Figures 5 and 6 is that, for any oscillation frequency, the qualitative results observed in Figures 3a and 4a are also observed, because the increase in the [C12min]+[NTf2]− concentration (Figures 3a and 5) and the alkyl chain length (Figures 4a and 6) leads to a reduction in the dilatational elasticity. 3.3. Compressibility. This methodology measures the inverse of the compressibility (c−1). Figure 7 shows the results of c −1 values for different concentrations of the IL [C12min]+[NTf2]− at different aging times. As evidenced in Figure 7, the addition of the IL [C12min]+[NTf2]− has a significant effect on the change of the interfacial film compressibility, consistent with the results presented by the dynamic tests (Figure 3a). In all aging times analyzed, a clear reduction in the inverse of compressibility can be seen. The addition of 50 or 100 ppm of [C12min]+[NTf2]− considerably reduces the value of this property. In more compressible films, these data indicate less rigid interfaces and a high tendency to the oil emulsion destabilization. To complement the results obtained in Figure 7, compression tests were performed to evaluate the compressibility of systems with different alkyl chain lengths of IL in the same concentration (100 ppm). Figure 8 shows the results.
The results of the inverse of compressibility (as seen in Figure 8) are consistent with the elasticity results (Figure 4a). In these results, the addition of IL increases the compressibility of the system (as a result of reducing c−1). It is also observed that increasing the alkyl chain length has a positive effect on reducing the inverse of the compressibility, thus suggesting less rigid and less stable emulsion films.13 3.4. Stability Tests. Emulsion stability tests were conducted to obtain a direct relation between the interfacial properties and the demulsification efficiency of the ILs studied. The results are shown in Figure 9. The results of the stability tests corroborate the analysis of the interfacial properties already presented. It is possible to observe that the emulsions containing IL with a large alkyl chain length (such as [C12min]+[NTf2]−) had a greater demulsification efficiency, where the separation between the phases is much more evident in this system compared to the others. The emulsions containing [C8min]+[NTf2]− also showed a consistent emulsion breaking efficiency. In these two systems, it was possible to observe a considerable reduction in the interfacial properties, consequently generating less rigid films and easier separation emulsions. The occurrence of the alteration in the characteristics of the interfacial film by the reduction of the viscous modulus by the IL [C12min]+[NTf2]− can explain this high efficiency at the emulsion breaking by this surfactant. The emulsions with the IL [C4min]+[NTf2]− and 9138
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(10) Chen, Z.; Peng, J.; Ge, L.; Xu, L. Chem. Eng. Sci. 2015, 130, 254−263. (11) Peña, A. A.; Hirasaki, G. J.; Miller, C. A. Ind. Eng. Chem. Res. 2005, 44, 1139−1149. (12) Al-Sabagh, A. M.; Nasser, N. M.; Abd El-Hamid, T. M. Egypt. J. Pet. 2013, 22, 117−127. (13) Hezave, A. Z.; Dorostkar, S.; Ayatollahi, S.; Nabipour, M.; Hemmateenejad, B. Colloids Surf., A 2013, 421, 63−71. (14) Guzmán-Lucero, D.; Flores, P.; Rojo, T.; Martínez-Palou, R. Energy Fuels 2010, 24, 3610−3615. (15) Silva, E. B.; Santos, D.; Alves, D. R. M.; Barbosa, M. S.; Guimarães, R. C. L.; Ferreira, B. M. S.; Guarnieri, R. A.; Franceschi, E.; Dariva, C.; Santos, A. F.; Fortuny, M. Energy Fuels 2013, 27, 6311− 6315. (16) Ekott, E. J.; Akpabio, E. J. J. Eng. Appl. Sci. 2010, 5, 447−452. (17) Spiecker, P. M.; Kilpatrick, P. K. Langmuir 2004, 20, 4022− 4032. (18) Alexandrov, N.; Marinova, K. G.; Danov, K. D.; Ivanov, I. B. J. Colloid Interface Sci. 2009, 339, 545−550. (19) Yarranton, H. W.; Sztukowski, D. M.; Urrutia, P. J. Colloid Interface Sci. 2007, 310, 246−252. (20) Oliveira, P. F.; Santos, I. C. V. M; Vieira, H. V. P.; Fraga, A. K.; Mansur, C. R. E. Fuel 2017, 193, 220−229. (21) Lashkarbolooki, M.; Ayatollahi, S.; Riazi, M. J. Chem. Eng. Data 2014, 59, 3624−3634. (22) Alves, D. R.; Carneiro, J. S. A.; Oliveira, I. F.; Façanha, F., Jr.; Santos, A. F.; Dariva, C.; Franceschi, E.; Fortuny, M. Fuel 2014, 118, 21−26. (23) Li, X.; Boek, E.; Maitland, G. C.; Trusler, J. P. M. J. Chem. Eng. Data 2012, 57, 1078−1088. (24) Sztukowski, D. M.; Yarranton, H. W. Langmuir 2005, 21, 11651−11658. (25) Rondón, M.; Pereira, J. C.; Bouriat, P.; Graciaa, A.; Lachaise, J.; Salager, J. L. Energy Fuels 2008, 22, 702−707. (26) Ortiz, D. P.; Baydak, E. N.; Yarranton, H.W. J. J. Colloid Interface Sci. 2010, 351, 542−555. (27) Pradilla, D.; Simon, S.; Sjöblom, J. Colloids Surf., A 2015, 466, 45−56. (28) Dicharry, C.; Arla, D.; Sinquin, A.; Graciaa, A.; Bouriat, P. J. Colloid Interface Sci. 2006, 297, 785−791.
without IL (only crude oil) presented a low separation between the phases, attributed to the high rigidity of the interfacial film, which delays the separation between the phases. Thus, these results are also consistent with the information obtained through the interfacial properties.
4. CONCLUSION In this work, the interfacial properties of a water/oil system with distinct ILs were obtained through different methodologies using the pendant drop technique. The results showed quantitatively and qualitatively that the addition of IL decreases the rigidity of the interfacial film by the reduction in the viscoelastic properties as a function of aging time, suggesting characteristics of a good destabilizing agent. A change in the viscoelastic characteristics of interfacial films has also been seen, evidenced by the reduction in the values of the phase angle and viscous modulus of systems containing ILs. The interfacial properties also show that an increasing alkyl chain length promotes the migration ability of these surfactants to the interface, thus increasing its capacity to decrease the dilatational elasticity and reducing the rigidity of the interfacial film. All of this information was well-correlated with the stability of the emulsions containing the ILs, corroborating the information that the increase of the IL alkyl chain length facilitates the separation between the phases as a result of its action at the interface.
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AUTHOR INFORMATION
Corresponding Author
*Telephone: +55-7932182157. E-mail: claudio.dariva@gmail. com. ORCID
Elton Franceschi: 0000-0002-2675-7250 César Costapinto Santana: 0000-0002-8962-173X Claudio Dariva: 0000-0002-5239-9039 Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS The authors thank CNPq, CAPES, and FAPITEC/SE (Brazilian funding agencies) and Petrobras (Petróleo Brasileiro S.A., Brazil) for supporting this work.
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REFERENCES
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