Shear-induced phase transitions in sucrose ester surfactant.
The behavior of a commercial sucrose stearate blend has been examined by means of various experimental techniques (differential scanning calorimetry, light polarization and electron microscopy, and rotational rheometry). A partial phase diagram in water has been established. It shows that the binary system forms a lamellar lyotropic mesophase and that the melting behavior is characterized by a lamellar gel-lamellar liquid crystalline phase transition. The identification of the liquid crystalline phase has been carried out from textural observation using polarization microscopy and freeze-fracture electron microscopy. At low surfactant concentrations, the phase transition has been followed through rheological experiments. Furthermore, a shear-induced transition, from the lamellar phase (sheets of surfactant bilayers including a few large multilamellar vesicles) to an onion phase, has been observed above a critical temperature of 43 degrees C. The vesicles so obtained did not relax over more than 3 weeks. The presence of a small ratio of distearate in the sugar ester blend seems to be the key to vesicle formation at low surface-active material concentration.
Sadtler
Véronique M
VM
Centre de Génie Chimique des Milieux Rhéologiquement Complexes, GEMICO-Groupe ENSIC, 1 rue Grandville, BP 451, F-54001 Cedex, Nancy, France. veronique.sadtler@ensic.inpl-nancy.fr
Guely
Michèle
M
Marchal
Philippe
P
Choplin
Lionel
L