| Abstract
| - Phase behavior and formation of self-assemblies in ternary water/ penta(oxyethylene) dodecyl ether (C12EO5)/amphiphilic silicone copolymer, poly(dimethylsiloxane)−poly(oxyethylene) (SimC3EO3.2) systems, wereinvestigated. These silicone copolymers are very hydrophobic because of the short EO chain and are essentiallywater-insoluble amphiphilic oils, similar to high alcohols or fatty acids. In general, the surfactant layer curvaturebecomes less positive upon addition of amphiphilic oils, similar to what happens with high alcohols or fattyacids. This is what is observed for m = 5.8. However, in the ternary water/C12EO5/Si25C3EO3.2 system, thesurfactant layer curvature becomes more positive, and micellar cubic, normal hexagonal, and bicontinuouscubic phases are also formed, although a lamellar liquid crystal forms only in the water−C12EO5 system. Inthe liquid crystal regions, it was found that Si25C3EO3.2 is not dissolved in the thin bilayer of the C12EO5lamellar phase, whereas the long and bulky Si25C3 chain forms an oil core in those cubic, hexagonal, andbicontinuous cubic phases, in which the surfactant is absorbed at the hydrophobic interface of each aggregate.Then, this opposite effect of added amphiphilic silicone copolymer or oil to the surfactant solution is attributedto the long and flexible Si25C3 chain which makes an oil pool inside the aggregates. This different behaviorof small and large SimC3 chains is also observed in the cloud temperatures. In fact, the cloud temperature ofC12EO5 aqueous solution decreases upon addition of Si5.8C3EO3.2, whereas it increases by adding a longhydrophobic chain, like Si14C3EO3.2 or Si25C3EO3.2 silicone oil. It was confirmed by DLS that long rod micelles,which are present in the water−C12EO5 system, become small spherical micelles upon addition of Si25C3EO3.2. Consequently, hydrophobic SimC3EO3.2 changes the micellar shape in two different ways dependingon the length of the SimC3 chain. For small chains (e.g., m = 5.8), the surfactant−copolymer layer curvaturechanges to less positive by forming a mixed layer. Long and bulky chains (e.g., m = 14, 25) make an oil coreand this tends to make the curvature more positive, being this effect pronounced with increasing the hydrophobicchain length.
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