The phase behavior of a long hydrophobic chain A-B-type silicone surfactant, Me 3 SiO-(Me 2 SiO) m-2 -Me 2 -SiCH 2 CH 2 CH 2 -O-(CH 2 CH 2 O) n H (Si m C 3 EO n ), in water was investigated by phase study and small-angle X-ray scattering (SAXS). The types of liquid crystals or self-organized structures are highly dependent on both EO-chain (n) and poly(dimethylsiloxane)-chain (m) lengths or the volume ratio of the EO chain to the total surfactant, nV EO /V S , which is related to the classical Griffin's HLB value. Reverse discontinuous cubic phase (I 2 ) for Si 14 C 3 EO 7.8 and Si 25 C 3 EO 7.8,12.2,15.8 , reverse hexagonal phase (H 2 ) for Si 14 C 3 EO 12 , lamellar (L R ) phase for Si 14 C 3 EO 15.8 and Si 25 C 3 EO 51.6 , and hexagonal (H 1 ) and discontinuous cubic (I 1 ) phases for Si 5.8 C 3 -EO 36.6,51.6 are formed. Hence, both hydrophobic and hydrophilic chains affect the surfactant layer curvature, but in an opposite way. On the other hand, the effective cross-sectional area per surfactant at the hydrophobic surface of self-organized structures, a S , increases with increasing m (or n) at constant n (or m). a S is related to the amphiphilicity of surfactant (surfactant size). Since the surfactant layer curvature changes from positive to negative with increasing m at constant n, the l eff /l max decreases with m, where l eff is the effective hydrophobicchain length and l max is the length of the chain in its fully extended form. Namely, the entropy loss of a long hydrophobic chain would be largely increased when it is stretched, and thus, long hydrophobic chain tends to be in a shrunk-bulky state. This causes the expansion of a S and the change in the surfactant layer curvature from positive to negative. In a similar mechanism, a S increases with increasing the EO-chain length, n, but the surfactant layer curvature changes from negative to positive.

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The Krafft temperature and solubilization power of ionic and nonionic surfactants in aqueous solutions are strongly affected by added polar oils such as amino-acid-based oils (e.g., N-acylamino acid esters, AAE), because they tend to be solubilized in the surfactant palisade layer. The Krafft temperatures of 5 wt.% sodium dodecyl sulfate (SDS)-water and octaoxyethylene octadecyl ether (C 18 EO 8 )-water systems largely decreases upon addition of AAE and 1-hexanol, whereas it decreases very slightly in isopropyl myristate (IPM) and n-dodecane. The lowering of the Krafft temperature can be explained by the same mechanism as the melting-temperature reduction of mixing two ordinary substances. Namely, the polar oils are solubilized in the surfactant palisade layer of micelles and reduce the melting temperature of hydrated solid-surfactant (Krafft temperature). On the other hand, non-polar oil such as dodecane is solubilized deep inside micelles and makes an oil pool. The solubilization of non-polar oil is enhanced by mixing surfactant with AAE due to an increase in micellar size.

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