78 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS PENTANOL + BUTYL ACETATE / / .-' ...'•x •,, .......... •-r\-' ' .. WATER SODIUM DODECYL SULFATE + BUTYL ACETATE PENTANOL + BUTYL ACETATE WATER SODIUM DODECYL SULFATE + BUTYL ACETATE Figure 4. When butyl acetate is introduced, an intermediate trend is found. Observe the unification of the W/O and the O/W areas at a butyl acetate fraction of 0.5 in the nonaqueous components of the system. A B Butyl acetate/(Butyl Butyl acetate/(Butyl acetate + pentanol) acetate + pentanol) Butyl acetate/(Butyl acetate + sodium dodecyl sulfate) Butyl acetate/(Butyl acetate + sodium dodecyl sulfate) 0.5 0.1 0.75 0.25

MICROEMULSIONS WITH ESTERS 79 PENTANOL + BUTOXYETHANOL WATER SODIUM DODECYL SULFATE --t- BUTOXYETHANOL Figure 5. Introducing butoxyethanol gave the most pronounced increase of the solubility area. Observe the unification of the W/O and the O/W areas at a butoxyethanol fraction of 0.25 in the non-aqueous components of the system, and the huge solubilization area at a corresponding fraction 0.5. 0.75 gave complete solubility towards the "surfactant" corner. Butoxyethanol/(Butoxyethanol + pentanol) Butoxyethanol/(Butoxyethanol + sodium dodecyl sulfate) -- ß -- 0.25 This enhanced interaction in turn causes an increased presence of the ester at the miceliar interface or in the liquid crystalline phase of the two-phase compositions. The higher concentration of the ester at the interface gave rise to an increase or reduction of the microemulsion area depending on the hydrocarbon chain length of the ester. The short chain homologues gave a destabilization of the lameliar liquid crystalline phase and a consequent increase of the microemulsion area, while the long chain esters would stabilize the liquid crystalline phase and hence reduce the microemulsion region. An example of the first mentioned mechanism is found in the rather pronounced structural changes in the presence of ethyl acetate (Figures 2A and 2B). The coalescence