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Neutron reflectivity profiles of a PLL/SDS spread film in D 2 O at different compression states: (A) monolayer (ML) region and (B) extended structure (ES) region; indices i-v are defined in Figure 1B; solid lines show the simulated ML models and fitted ES models. (C) Variation of Π (black line) and fitted extended structure coverage (violet squares) with respect to the time; black and violet arrows indicate film collapse and the onset of extended structures, respectively; variation of area versus time is also shown.

Neutron reflectivity profiles of a PLL/SDS spread film in D 2 O at different compression states: (A) monolayer (ML) region and (B) extended structure (ES) region; indices i-v are defined in Figure 1B; solid lines show the simulated ML models and fitted ES models. (C) Variation of Π (black line) and fitted extended structure coverage (violet squares) with respect to the time; black and violet arrows indicate film collapse and the onset of extended structures, respectively; variation of area versus time is also shown.

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Article
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Reversible control of the 3D structure of polyelectrolyte/surfactant films at the air/water interface is showcased. A recently discovered mechanism is exploited to form highly efficient, stable and biocompatible films by spreading aggregates composed of poly-L-lysine and sodium dodecyl sulfate on the surface of water. Reversible control of: (1) the...

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Context 1
... scope is to resolve the change in thickness or coverage of the extended structures with respect to film compression. Data prior to the collapse (states i, ii and iii in Figure 1B), combined with simulations of the reflectivity profiles based on the coverage of the surface monolayer from Figure 1C, show that changing monolayer coverage indeed has a small effect on the data ( Figure 3A). However, data after the collapse (states iii, iv and v), combined with fits of the volume fraction at a constant extended structure thickness of 21.8 Å reveal the higher sensitivity of the measurements to the coverage of the extended structure ( Figure 3B). ...
Context 2
... prior to the collapse (states i, ii and iii in Figure 1B), combined with simulations of the reflectivity profiles based on the coverage of the surface monolayer from Figure 1C, show that changing monolayer coverage indeed has a small effect on the data ( Figure 3A). However, data after the collapse (states iii, iv and v), combined with fits of the volume fraction at a constant extended structure thickness of 21.8 Å reveal the higher sensitivity of the measurements to the coverage of the extended structure ( Figure 3B). By comparison, fits of the data after the collapse to a model where the thickness of the extended structure changes at a constant volume fraction exhibited significantly worse agreement, as revealed by an increase of up to 30% in the global χ 2 parameter (ESI section 7). ...
Context 3
... can be concluded that after collapse of the surface monolayer, the coverage of discrete patches of the wrapped bilayer or hemimicelles can now be controlled. The coverage of extended structures, in comparison with the variation of Π, as a function of time is displayed ( Figure 3C). The extended structures start to form (violet arrow) at the collapse (black arrow). ...

Citations

... Even though NR is traditionally known as a powerful but slow technique, recent significant improvements in instrumentation have opened the technique to time-resolved studies [22]. Indeed, over the last few years, kinetic studies on the interactions of peptides with lipid monolayers have successfully resolved the interfacial composition of binary mixtures on the minute time scale [23], and it is now even possible to resolve the 3D structural dynamics of polymer/surfactant mixtures [24]. Most relevant to the present work, the first quantitative assessment was published last year on the time-resolved interactions of fluorocarbon oil vapor with lipid monolayers, thanks to the combined application of ellipsometry and NR [25]. ...
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