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- Ederth, Thomas, et al.
(författare)
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A neutron reflectivity study of drainage and stratification of AOT foam films
- 2003
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 19:19, s. 7727-7733
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Tidskriftsartikel (refereegranskat)abstract
- Structural properties of Aerosol-OT (AOT) foam films were studied by neutron reflectometry. The drainage of large (10 cm(2)), horizontally oriented AOT films under zero applied external pressure is slow and proceeds from thick colored or gray films to black films of approximately 200 Angstrom thickness over many hours, resulting in quasi-static conditions over the time scales required for the acquisition of reflectivity profiles throughout the whole drainage process. After formation of the foam film-while still showing colored interference fringes-and during the early stages of thinning, the appearance of Bragg diffraction peaks demonstrates that the film contains multilamellar structure, in agreement with studies at free air/water interfaces. Upon further reduction of the film thickness, below approximately 250 Angstrom, the reflectivity profile is well fitted by a three-layer slab model with two surfactant layers and an aqueous core with a high surfactant content. The composition of the aqueous core and the manner in which the reflectivity during the latter stages of draining evolves from Bragg peaks to a Kiessig fringe structure indicate stratification within the thin foam film.
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| 2. |
- Ederth, Thomas, et al.
(författare)
-
Force measurements between semifluorinated thiolate self-assembled monolayers : Long-range hydrophobic interactions and surface charge
- 2001
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Ingår i: Journal of Colloid and Interface Science. - : Elsevier BV. - 0021-9797 .- 1095-7103. ; 235:2, s. 391-397
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Tidskriftsartikel (refereegranskat)abstract
- Long-range interactions between self-assembled monolayers (SAMs) of semifluorinated alkanethiols have been studied by direct force measurements in water and aqueous NaCl solutions. SAMs prepared from three different thiols, with identical fluorinated head groups but varying hydrocarbon spacer lengths, were investigated: CF3(CF2)(9)(CH2)(x)SH, where x = 2, 11, or 17. Force measurements show that the interactions in water and electrolyte solutions are composed of both double-layer interactions emerging from what appears to be charges adsorbed onto the surfaces and long-range "hydrophobic" attractions, in excess of the expected van der Waals forces. The three investigated thiols produce similar results in force measurements, though the contact angles with water are slightly different, The "hydrophobic" attraction has the form of step-like attractive discontinuities in the force profiles at separations ranging from 20 to 40 nm, caused by bridging of microscopic bubbles residing at the surfaces, The shape or range of these discontinuities are not significantly affected by replacement of the water with either 1 mM or 1 M NaCl solutions. The origin of the charges causing the electrostatic double-layer interaction is unclear, but some possible causes are discussed.
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