Thermotropic behavior of poly(oxyethylene) cholesterol ethers.
The thermotropic behavior of poly(oxyethylene) cholesterol ether surfactants was studied by differential scanning calorimetry and small-angle X-ray scattering. Contrary to what is usually observed in conventional poly(oxyethylene)-type surfactant systems, poly(oxyethylene) cholesterol ether surfactants show a change of the fusion mechanism as the chain length is varied. For long chain lengths (n > or = 15) the usual solid-liquid transition is found, but for short chain lengths (n < or = 10) the transition goes through a birefringent lamellar phase. The appearance of this liquid crystal (LC) phase seems to be related with the predominance of the cholesterol part in the short chain polyoxyethylene surfactants. On the contrary, for long polyexyethylene chains the polymer gains in importance and only a solid crystalline structure is observed at low temperatures. An antiparallel packing structure with totally overlapped chains is found for both, the solid and the LC phase. The chains seem to be in a zigzag configuration, and only for the longest surfactant here studied (n = 30) a change of the chain configuration to a much shorter meander configuration is observed.
López-Quintela
M Arturo
MA
Departamento de Química Física, Facultad de Química, Universidad de Santiago, Santiago de Compostela, E-15782, Spain.
Akahane
Akira
A
Rodríguez
Carlos
C
Kunieda
Hironobu
H
D002152:Calorimetry, Differential Scanning; D002784:Cholesterol / Q000031:analogs & derivatives* / Q000737:chemistry; D011092:Polyethylene Glycols / Q000737:chemistry*; D012542:Scattering, Radiation; D053838:Scattering, Small Angle; D013501:Surface-Active Agents / Q000737:chemistry; D013696:Temperature; D013816:Thermodynamics; D014965:X-Rays
D013501:Surface-Active Agents; C095164:poly(oxyethylene) cholesteryl ether; D011092:Polyethylene Glycols; D002784:Cholesterol