Abstract
In the millimolar concentration domain (typically 1 mM), dioctadecyldimethylammonium bromide and chloride (DODAX, X representing Br− or Cl− counterions) molecules assemble in water as large unilamellar vesicles. Differential-scanning calorimetry (DSC) is a suitable technique to obtain the melting temperature (T m) characteristic of surfactant bilayers, while fluorescence spectroscopy detects formation of surfactant aggregates, like bilayers. These two techniques were combined to investigate the assembly of DODAX molecules at micromolar concentrations, from 10 to 100 μM. At 1 mM surfactant, T m ≈ 45 °C and 49 °C, respectively, for DODAB and DODAC. DSC and fluorescence of Nile Red were used to show the formation of DODAX aggregates, at the surfactant concentration as low as 10 μM, whose T m decreases monotonically with increasing DODAX concentration to attain the value for the ordinary vesicles. The data indicate that these aggregates are organized as bilayer-like structures.
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Acknowledgments
FRA thanks CNPq for the PhD grant. EF thanks CNPq and FAPESP. EMSC and MECDRO thank Fundação para a Ciência e a Tecnologia (Portugal) for funding through Centro de Física da Universidade do Minho. Dr. W. Loh is acknowledged for kindly supplying the DSC equipment.
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Feitosa, E., Alves, F.R., Castanheira, E.M.S. et al. DODAB and DODAC bilayer-like aggregates in the micromolar surfactant concentration domain. Colloid Polym Sci 287, 591–599 (2009). https://doi.org/10.1007/s00396-009-2008-1
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DOI: https://doi.org/10.1007/s00396-009-2008-1