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Title

Formation and properties of reverse micellar cubic liquid crystals and derived emulsions

AuthorsRodríguez-Abreu, Carlos CSIC ORCID; Shrestha, Lok Kumar; Varade, Dharmesh; Aramaki, Kenji; Maestro, Alicia; López Quintela, Arturo; Solans, Conxita CSIC ORCID
KeywordsReverse micellar
Cubic liquid crystals
Water droplets
Elastic modulus
Viscosity
Polymerizable oils
Issue Date2-Oct-2007
PublisherAmerican Chemical Society
CitationLangmuir 23(22): 11007-11014 (2007)
AbstractThe 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 10^4 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.Atemperature 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.
Description8 pages, 11 figures.-- PMID: 17910486 [PubMed].-- Supporting information (Suppl. figures S1-S3, 3 pages) available at: http://pubs.acs.org/doi/suppl/10.1021/la701722f/suppl_file/la701722f-file001.pdf
Printed version published Oct 23, 2007
Publisher version (URL)http://dx.doi.org/10.1021/la701722f
URIhttp://hdl.handle.net/10261/9602
DOI10.1021/la701722f
ISSN1520-5827
Appears in Collections:(IQAC) Artículos

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