STERIC REPULSION OF POLYOXYETHYLENE GROUPS FOR EMULSION STABILITY

Rapid coalescence was studied on liquid paraffin emulsion stabilized with a series of poly(oxyethylene)dodecyl ethers [C12H25(EO)n, n = 1, 2, 3, 4, 5, 6, 7, 8] and of poly(oxyethylene)nonylphenyl ethers [C9H19-PHI(EO)n, n = 2, 4, 5, 6, 12]. The turbidity of emulsion was measured as a function of the solution pHs at constant ionic strength of 0.1 mol dm-3. As a result, it was found that the emulsions (which were formed with C12H25(EO)n surfactants having less than four oxyethylene groups, or with C9H19-PHI(EO)n surfactants having less than six oxyethylene groups) brought about rapid coalescence in the bulk pH between 2.0 approximately 3.5, which corresponded to the zero point of charges for the emulsions of the present systems. According to the Tadros treatment for emulsion flocculation, the total flocculation potential was estimated as a function of the distance relative to the number of oxyethylene groups in the surfactants. The critical coalescence energy was obtained as - 3.43 x 10(-19) J for the C12H25(EO)n surfactants and - 2.14 x 10(-19) J for the C9H19-PHI(EO)n surfactants. Furthermore, the formation of a hole for coalescence was estimated under the simple assumption that the coalescence was caused only by the energy dissipation.