Complex Emulsion Inversion Pattern Associated with the Partitioning of Nonionic Surfactant Mixtures in the Presence of Alcohol Cosurfactant Shirley Marfisi, †,‡ Marı ´a Patricia Rodrı ´guez, † Gabriela Alvarez, † Marı ´a-Teresa Celis, † Ana Forgiarini, † Jean Lachaise, ‡ and Jean-Louis Salager* ,† Laboratorio FIRP, Ingenierı ´a Quı ´mica, Universidad de Los Andes, Me ´ rida, Venezuela, and Laboratoire de Fluides Complexes, UMR 5150, Universite ´ de Pau P.A., France Received February 19, 2005. In Final Form: May 6, 2005 Commercial ethoxylated nonionic surfactant mixtures containing alcohol cosurfactant exhibit a three- phase behavior whose formulation strongly varies with the water/oil ratio. As a consequence, a change in water/oil ratio can result in a sequence of up to three different emulsion inversion processes, through a combination of formulation and composition effects. Introduction It was shown in recent publications that dynamic emulsion inversion is quite dependent on the experimental protocol, 1-11 that is, the delay to inversion is related to the way the experiment is carried out. However, dynamic inversion always takes place at or after the crossing of the so-called standard inversion line, which is thus of primary importance. The standard inversion line is associated with phase behavior and may be represented on three different types of bidimensional diagrams: surfactant-oil-water (SOW) ternary at constant formulation and temperature, for- mulation (or temperature) versus surfactant concentration at constant water-to-oil ratio (WOR), and formulation (or temperature) versus WOR at constant surfactant con- centration. Since the most important variables to trigger inversion are the formulation variables (including tem- perature) and the water/oil composition 12 the most suited representation to study emulsion inversion seems to be the formulation (or temperature)-composition (WOR) map. 13 The phase behavior of SOW systems essentially depends on the relative affinity of the surfactant for the oil and water phases, and a swap in surfactant affinity is directly associated with the phase behavior transition. According to Winsor’s pioneering work, 14,15 when the interactions between surfactant and water (respectively, oil) are dominant, the phase behavior of the system is the so-called Winsor I type noted WI, (respectively, Winsor II type noted WII), and an aqueous (respectively, oily) microemulsion is in equilibrium with an excess predomi- nantly oily (respectively, aqueous) phase. Between these two-phase behavior cases, a three-phase behavior (noted WIII) prevails, in which a bicontinuous microemulsion is in equilibrium with both aqueous and oily excess phases. Such a behavior depends on several physicochemical parameters, whose effects can be gathered in a single formulation variable, so-called the surfactant affinity difference (SAD) or its dimensionless equivalent the hydrophilic lipophilic deviation (HLD). 16 The HLD is some kind of system hydrophilic-lipophilic balance, i.e., it is a quantitative measurement of the deviation from balanced formulation, in terms of all formulation or field variables. This generalized formulation variable has been shown to be related to the partition coefficient of the surfactant between the two phases. 16 It is essentially equivalent to an empirical expression found 25 years ago for the attainment of three-phase behavior, which is as follows for nonionic systems: 17 where R is a characteristic parameter of the hydrophobic part of the surfactant, EON is the number of ethylene oxide groups per surfactant molecule, ACN is the number of carbon atoms in the alkane molecule (or equivalent EACN), S is the salinity of the aqueous phase in wt % NaCl (or equivalent), Φ(A) is a function of alcohol type and concentration, T is the temperature (°C), and T ref is generally taken at 25 °C; k, b, and c T are constants, * Corresponding author. E-mail: salager@ula.ve. † Universidad de Los Andes. ‡ Universite ´ de Pau P.A. (1) Salager, J. L.; Marquez, L.; Pen ˜ a, A.; Rondon, M.; Silva, F.; Tyrode, E. Ind. Eng. Chem. Res. 2000, 39, 2665. (2) Silva, F.; Pen ˜ a, A.; Min ˜ ana-Perez, M.; Salager, J. L. Colloids Surf., A 1998, 132, 221. (3) Pen ˜ a, A.; Salager, J. L. Colloids Surf., A 2001, 181, 319. (4) Sajjadi, S.; Zerfa, Z.; Brooks, B. W. Chem. Eng. Sci. 2002, 57, 663. (5) Sajjadi, S.; Jahanzad, F.; Brooks, B. W. Ind. Eng. Chem. Res. 2002, 41, 6033. (6) Zambrano, N.; Tyrode, E.; Mira, I.; Marquez, L.; Rodrı ´guez, M. P.; Salager, J. L. Ind. Eng. Chem. Res. 2003, 42, 50. (7) Mira, I.; Zambrano, N.; Tyrode, E.; Marquez, L.; Pen ˜ a, A. A.; Pizzino, A.; Salager, J. L. Ind. Eng. Chem. Res. 2003, 42, 57. (8) Tyrode, E.; Mira, I.; Zambrano, N.; Ma ´ rquez, L.; Rondo ´n-Gonzalez, M.; Salager, J. L. Ind. Eng. Chem. Res. 2003, 42, 4311. (9) Bouchama, F.; van Aken, G. A.; Autin, A. J. E.; Koper, G. J. M. Colloids Surf., A 2003, 231, 11. (10) Sajjadi, S.; Jahanzad, F.; Yianneskis, M.; Brooks, B. W. Ind. Eng. Chem. Res. 2003, 42, 3571. (11) Tyrode, E.; Allouche, J.; Choplin, L.; Salager, J. L. Ind. Eng. Chem. Res. 2005, 44, 67. (12) Salager, J. L. In Encyclopedia of Emulsion Technology; Becher, P., Ed.; Marcel Dekker: New York, 1988; Vol. 3, pp 79-134. (13) Salager, J. L.; Min ˜ ana-Perez, M.; Perez-Sanchez, M.; Ramirez- Gouveia, M.; Rojas, C. I. J. Dispersion Sci. Technol. 1983, 4, 313. (14) Winsor, P. A. Solvent Properties of Amphiphilic Compounds; Butterworth: London, 1954. (15) Bourrel, M.; Schechter, R. S. Microemulsion and Related Systems; Marcel Dekker: New York, 1988. (16) Salager, J. L.; Marquez, N.; Graciaa, A.; Lachaise, J. Langmuir 2000, 16, 5534. (17) Bourrel, M.; Salager, J. L.; Schechter, R. S.; Wade, W. H. J. Colloid Interface Sci. 1980, 75, 451. HLD )R- EON - kACN + bS + Φ(A) + c T (T - T ref ) (1) 6712 Langmuir 2005, 21, 6712-6716 10.1021/la050450a CCC: $30.25 © 2005 American Chemical Society Published on Web 06/23/2005