Effect of Surfactants on the Interfacial Tension and Emulsion Formation between Water and Carbon Dioxide

Abstract

The lowering of the interfacial tension (γ) between water and carbon dioxide by various classes of surfactants is reported and used to interpret complementary measurements of the capacity, stability, and average drop size of water-in-CO2 emulsions. γ is lowered from ∼20 to ∼2 mN/m for the best poly(propylene oxide)-b-poly(ethylene oxide)-b-poly(propylene oxide) (PPO-b-PEO-b-PPO) and PEO-b-PPO-b-PEO Pluronic triblock copolymers, 1.4 mN/m for a poly(butylene oxide)-b-PEO copolymer, 0.8 mN/m for a perfluoropolyether (PFPE) ammonium carboxylate and 0.2 mN/m for PDMS24-g-EO22. The hydrophilic−CO2-philic balance (HCB) of the triblock Pluronic and PDMS-g-PEO−PPO surfactants is characterized by the CO2-to-water distribution coefficient and “V-shaped” plots of log γ vs wt % EO. A minimum in γ is observed for the optimum HCB. As the CO2-philicity of the surfactant tail is increased, the molecular weight of the hydrophilic segment increases for an optimum HCB. The stronger interactions on both sides of the interface lead to a lower γ. Consequently, more water was emulsified for the PDMS-based copolymers than either the PPO- or PBO-based copolymers.

Near-Surface Composition Profiles and the Adhesive Properties of Statistical Copolymer Films Being Model Systems of Pressure Sensitive Adhesive Films

“…The literature values of the surface tensions of the involved homopolymers are γ(PEHA) ) 30 mN/m and γ(PMMA) ) 38.5 mN/m (54,55). Thus an equilibrium structure is installed by minimizing the surface free energy.…”

Interfacial phenomena at the compressed co2-water interface

“…The γ of the C|W interface (γ C|W ) at moderate pressures is ~ 20 mN/m (da Rocha, et al, 1999). The value of ~ 50 mN/m which is much lower than those generally observed in conventional O|W systems (Freitas, et al, 1997), dictates the much lower surfactant requirement for the C|W interface i.e.…”

“…02, pp. 183 -190, April -June, 2006 Many amphiphiles have also been shown to have an appropriate balance, as revealed by the decrease in the interfacial tension at the C|W interface (γ C|W ) (da Rocha, et al, 1999). However, W/C microemulsions have much stronger attractive interactions than their W/O counterparts, a fact that has been attributed to the enhanced strength of attractive tail-tail interactions between approaching microemulsion droplets (Lee, et al, 2001), which is directly manifested by the high pressures generally required for their stabilization.…”

“…These properties have been determined using the pendant drop technique, adapted to high-pressure systems (da Rocha, et al, 1999). The area occupied per surfactant molecule at the interface A (=1/Γ) can be calculated with the help of the Gibbs-Adsorption equation:…”

“…Rocha et al, 1999using WinDig software (da Rocha, et al, 1999. The [c s ] indicated by the arrows is the critical aggregation concentration (cac).…”