Effect of mixing oils on the hexagonal liquid crystalline structures

Citation
H. Kunieda et al., Effect of mixing oils on the hexagonal liquid crystalline structures, J PHYS CH B, 104(9), 2000, pp. 2005-2011
Citations number
21
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Physical Chemistry/Chemical Physics
Journal title
JOURNAL OF PHYSICAL CHEMISTRY B
ISSN journal
1520-6106 → ACNP
Volume
104
Issue
9
Year of publication
2000
Pages
2005 - 2011
Database
ISI
SICI code
1520-6106(20000309)104:9<2005:EOMOOT>2.0.ZU;2-A
Abstract
Structural change in hexagonal liquid crystal (H-1) in the water/heptaoxyet hylene dodecyl ether (C12EO7) system upon addition of mixed oil (m-xylene decane) is investigated by phase study and small-angle X-ray scattering (S AXS). The surfactant layer curvature tends to be less positive or negative upon addition of the mixed oil at a high m-xyleneldecane ratio, and the H-1 -L-alpha (lamellar liquid crystal) transition takes place. At a low m-xylen e/decane ratio, however, the H-1-I-l transition occurs with increasing mixe d oil content, where I-l is a discontinuous micellar cubic phase. An excess oil phase directly separates from the H-1 phase at a moderate m-xyleneldec ane ratio. The change in the effective cross sectional area per surfactant, a(S), as a function of oil content was also measured at each mixing fracti on of oils by SAXS. m-Xylene molecules tend to penetrate the surfactant pal isade layer and widen a(S), whereas decane molecules tend to be solubilized in the deep core of surfactant hydrophobic moieties and the us is not larg ely expanded. The a(S) does not jump at each transition of H-1-I-l and H-1- L-alpha. Considering the volume of polyoxyethylene chain (EO chain), the re pulsion between the EO chains may increase upon addition of decane, whereas it would decrease upon addition of m-xylene. To balance the repulsion with the attraction due to the interfacial tension between water and the lipoph ilic part without the big change in a(S), the phase transitions take place but the change in the surfactant layer curvature is opposite in both oil sy stems.