Nanoemulsions Induced by Compressed Gases

Abstract

Pressure makes the difference! Compressed gases, such as CO2, ethylene, ethane, and propane, can induce the formation of nanoemulsions with special characteristics. The application of CO2‐induced nanoemulsions in the preparation of cross‐linked porous polystyrene materials and the ability of CO2 to stabilize emulsions for enhanced oil recovery are studied. A possible mechanism for the formation of the nanoemulsions is discussed (see picture).

Radical polymerization of miniemulsions induced by compressed gases

“…It is generally assumed that the smallest droplets are obtained in the transparent region, although this effect has yet to be conclusively demonstrated. Similar results have been found using gases other than CO 2 (ethylene, ethane, and propane), 36 and the effect of CO 2 is thus not related to an induced reduction in pH of the aqueous phase.…”

“…That is, the droplet size of the initial emulsion becomes smaller due to the presence of CO 2 , enabling monomer droplet nucleation to be a dominant mechanism consistent with previous reports. 36,42 However, the droplet size appears not to be sufficiently small for exclusive droplet nucleation to occur. Therefore, droplets and micellar/ homogeneous nucleation co-exist in the system at P T , i.e.…”

“…39,40 It has been proposed that the transparency induced by compressed gases is related to the insertion of gas molecules into the interfacial lm, resulting in a change in the curvature and creating smaller droplets. 36 The transparent emulsion formed via CO 2 pressurization of TX-100 (poly(oxyethylene)iso-octylphenyl ether)/water/ isooctane at P T ¼ 3.90 MPa was characterized by small-angle Xray scattering (SAXS), yielding spherical droplets of diameter 92 nm. 41 However, a typical miniemulsion with a diameter of 92 nm is not transparent but milky white.…”

Preparation of silica sphere with porous structure in supercritical carbon dioxide

“…The resultant white solid was filtered, dried at 50°C and finally, calcined at 600°C in air for 8 h to remove the surfactant. It has to be mentioned that higher density of CO 2 was needed to achive the best synthesis condition because larger density of CO 2 might raise the chemical association between CO 2 and the water molecules concentrated in the head group of the surfactant to form emulsion, stabilized by the surfactant [38,39]. Therefore, CO 2 pressure was varied between 7 and 18 MPa to obtain spherical silica structure.…”

“…In the present system, the synthesis gel exposed to CO 2 contains water, cationic surfactant CTAB and silica source TEOS. Now, it is possible to generate compressed gas-induced emulsion by CO 2 and water in the presence of surfactant, which will play an important role to stabilize the emulsion [38,54]. CTAB is a polar molecule and having very low solubility in CO 2 .…”