title: Formation and properties of reverse micellar cubic liquid crystals and derived emulsions.
abstract: The structure of the reverse micellar cubic (I2) liquid crystal and the adjacent micellar phase in amphiphilic block copolymer/water/oil systems has been studied by small-angle X-ray scattering (SAXS), rheometry, and differential scanning calorimetry (DSC). Upon addition of water to the copolymer/oil mixture, spherical micelles are formed and grow in size until a disorder-order transition takes place, which is related to a sudden increase in the viscosity and shear modulus. The transition is driven by the packing of the spherical micelles into a Fd3m cubic lattice. The single-phase I2 liquid crystals show gel-like behavior and elastic moduli higher than 104 Pa, as determined by oscillatory measurements. Further addition of water induces phase separation, and it is found that reverse water-in-oil emulsions with high internal phase ratio and stabilized by I2 liquid crystals can be prepared in the two-phase region. Contrary to liquid-liquid emulsions, both the elastic modulus and the viscosity decrease with the fraction of dispersed water, due to a decrease in the crystalline fraction in the sample, although the reverse emulsions remain gel-like even at high volume fractions of the dispersed phase. A temperature induced order-disorder transition can be detected by calorimetry and rheometry. Upon heating the I2 liquid crystals, two thermal events associated with small enthalpy values were detected: one endothermic, related to the "melting" of the liquid crystal, and the other exothermic, attributed to phase separation. The melting of the liquid crystal is associated with a sudden drop in viscosity and shear moduli. Results are relevant for understanding the formation of cubic-phase-based reverse emulsions and for their application as templates for the synthesis of structured materials.
authors.affiliation: Institut d'Investigacions Químiques i Ambientals de Barcelona, Consejo Superior de Investigaciones Científicas (IIQAB/CSIC), Jordi Girona, 18-26, 08034 Barcelona, Spain. craqci@cid.csic.es
authors.forename: Carlos
authors.initials: C
authors.lastname: Rodríguez-Abreu
authors.forename: Lok Kumar
authors.initials: LK
authors.lastname: Shrestha
authors.forename: Dharmesh
authors.initials: D
authors.lastname: Varade
authors.forename: Kenji
authors.initials: K
authors.lastname: Aramaki
authors.forename: Alicia
authors.initials: A
authors.lastname: Maestro
authors.forename: Arturo López
authors.initials: AL
authors.lastname: Quintela
authors.forename: Conxita
authors.initials: C
authors.lastname: Solans