The Effect of Fluctuations on Bilayer and Monolayer Systems: High-Resolution X-ray Scattering Study of a Three-Component Lamellar Phase
✍ Scribed by Reiko Oda; Simon G. Mochrie
- Publisher
- Elsevier Science
- Year
- 1997
- Tongue
- English
- Weight
- 169 KB
- Volume
- 190
- Category
- Article
- ISSN
- 0021-9797
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✦ Synopsis
for a certain range of concentration, one can change continu-We have investigated the effect of symmetry on the fluctuation ously from a bilayer system to a monolayer system and then of a three-component lamellar phase composed of oil (octane), to an inverted bilayer system by changing the ratio of oil water, and a nonionic surfactant (C12E5). The studied lamellae and water at fixed surfactant concentration. By means of consist of various oil/water volume ratios for a fixed surfactant high-resolution X-ray scattering, it is possible to determine concentration. From aligned lamellae, we succeeded in obtaining very precisely the membrane periodicity. We observe that highly reproducible, high-resolution X-ray spectra with very small the scattering shows very small, but reproducible, variations full width at half maximum (6 1 10 04 A ˚01 ). The deviation of the of the periodicity of the layers as a function of the temperaperiodicity expected by the dilution law can be explained from the ture as well as of the oil-to-water ratio. The periodicity variafluctuations. Measuring this deviation, we observed that for the constant surfactant concentration, lamellae with equal oil/water tion of lamellar phase with temperature can be described ratios have higher fluctuation than when oil/water r 0 or ϱ beusing the logarithmic correction introduced by Roux et al. cause of the difference of the flexibility of monolayers and bilayers (5), which states the following: the larger membrane's peri-᭧ 1997 Academic Press odicity corresponds to a system with increased membrane Key Words: lamellae; high-resolution X-ray scattering; logarithundulations. The ratio of membrane area which is projected mic correction.
on the xy plane perpendicular to the symmetry axis to real membrane area is thereby decreased. Requiring a fixed quantity of surfactant per unit area, the periodicity thus is EXPERIMENTAL frich interaction) exists always, and it originates in loss of entropy caused by confining a membrane between its neighboring membranes. One feature of lamellar phases is that
The surfactant C12E5, with a purity ú99%, was bought from Fluka Chemical Co. and was used without further purification. The octane, with a purity of ú99.5%, was also 1 To whom correspondence should be addressed. Present address: Laborabought from Fluka. The surfactant was found to oxidize and toire d'Ultrasons et de Dynamique des Fluides Complexes (L.U.D.F.C), 3 degrade with time, so extreme precautions were taken and