(232j) Effect of Surfactant Phase Behavior and Structure on Emulsification Process and Emulsion Stability

In order to improve our understanding of the effects that the equilibrium phase behavior and structure of amphiphilic molecules (e.g., surfactants, lipids, block copolymers) have on the emulsification process and the properties of emulsions stabilized by these amphiphiles, we have exploited the known phase behavior of poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) amphiphilic block copolymers (Pluronics or Poloxamers) [1] in the presence of two immiscible solvents. Specifically, we considered ternary systems consisting of Pluronic F38 [2], L64 [3], P84 [4], P104 [5], or L121 [2] with water and p-xylene which exhibit a very rich phase behavior, including a variety of water-continuous and oil-continuous lyotropic liquid crystalline (LLC) phases. We prepared emulsions having the same (final) compositions but through different emulsification paths, and evaluated the emulsions on the basis of homogeneity and droplet size. We found finer and more homogenous emulsions to result when oil-in-lamellar structures (as revealed by small-angle X-ray scattering) were formed during the emulsification process, or when the emulsification path traversed the lamellar LLC phase [6]. This can be attributed to the favorable properties of the lamellar structure: high oil solubilization capacity with concurrent facile dispersibility in water, relatively low interfacial tension, and relatively low viscosity. The findings reported here are relevant to the preparation of emulsions for diverse applications such as skin-care products, pharmaceuticals, food products, coatings, inks, agrochemicals, oil dispersants, and nanomaterials synthesis.

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[3] Alexandridis, P.; Olsson, U.; Lindman, B., Self-assembly of amphiphilic block copolymers: The (EO)13(PO)30(EO)13 - water - p-xylene system. Macromolecules 1995, 28 (23), 7700-7710. DOI: 10.1021/ma00127a016

[4] Alexandridis, P.; Olsson, U.; Lindman, B., A record nine different phases (four cubic, two hexagonal, and one lamellar lyotropic liquid crystalline and two micellar solutions) in a ternary isothermal system of an amphiphilic block copolymer and selective solvents (water and oil). Langmuir 1998, 14 (10), 2627-2638. DOI: 10.1021/la971117c

[5] Svensson, B.; Alexandridis, P.; Olsson, U., Self-assembly of a poly(ethylene oxide) / poly(propylene oxide) block copolymer (Pluronic P104, (EO)27(PO)61(EO)27) in the presence of water and xylene. J. Phys. Chem. B 1998, 102 (39), 7451-7548. DOI: 10.1021/jp981789r

[6] Kaizu, K.; Alexandridis, P., Effect of surfactant phase behavior on emulsification. J. Colloid Interface Sci. 2016, 466, 138-149. DOI: 10.1016/j.jcis.2015.10.016.