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DOI: 10.1039/A605373D (Paper) Reference Section for: J. Chem. Soc., Faraday Trans., 1997, 93, 453-455

Reorganisation of alkyl chains in vesicles formed in aqueous solution by dialkyldimethylammonium bromide, R2N+Me2Br- where R=C12H25, C14H29, C16H33 or C18H37

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Michael J. Blandamer, Barbara Briggs, Paul M. Cullis, Stuart D. Kirby and Jan B. F. N. Engberts

Abstract

Differential scanning calorimetry (DSC) scans are reported for aqueous solutions containing vesicles formed by four dialkyl-dimethylammonium bromides; R2N+Me2Br- where R=dodecyl (DDAB), tetradecyl (DTAB), hexadecyl (DHAB) or octadecyl (DOAB). Electron micrographs of DTAB (aq; 2×10-3 mol dm-3) confirmed that these solutions, prepared at 50°C, contain vesicles, with radii ca. 700 nm. DSC scans of these solutions, initially cooled to 5°C and then scanned with increasing temperature, showed no evidence of an extremum in isobaric heat capacity as a function of temperature, associated with a chain-packing transition in the vesicular bilayer at a characteristic temperature, Tm. However, clear evidence for such a transition near 29°C was obtained after this solution had been held at 5°C for periods up to 11 h. With increase in the time during which the DTAB solution was held at 5°C, the recorded signal associated with the melting temperature increased in intensity. However, there was again no evidence for this transition if the solution was cooled to 5°C and the heat capacity dependence on temperature immediately re-scanned. The patterns are discussed in terms of a kinetic control, during cooling, of the packing of dialkyl chains in the bilayers. A similar pattern was observed for DDAB (aq) where Tm=15.8°C. In the case of DHAB (aq) where Tm=28.1°C, no kinetic features were apparent using DSC to study the gel to chain-packing transition.

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