| 1. |
- Gustavsson, Charlotte, et al.
(författare)
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Water-Responsive Internally Structured Polymer Surfactant Films on Solid Surfaces
- 2014
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 30:42, s. 12525-12531
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Tidskriftsartikel (refereegranskat)abstract
- Water-insoluble films of oppositely charged polyionsurfactant ion complex salts (CS) are readily cast on solid surfaces from ethanolic solutions. The methodology introduces new possibilities to study and utilize more or less hydrated CS. Direct SAXS measurements show that the surface films are water-responsive and change their liquid crystalline structure in response to changes in the water activity of the environment. In addition to the classical micellar cubic and hexagonal phases, a rectangular ribbon phase and a hexagonal close-packed structure have now been detected for CS composed of cationic alkyltrimethylammonium surfactants with polyacrylate counterions. Added cosurfactants, decanol or the nonionic surfactant C12E5, yield additional lamellar and bicontinuous cubic structures. Images of the surfaces by optical and atomic force microscopy show that the films cover the surfaces well but have a more or less irregular surface topology, including craters of sizes ranging from a few to hundreds of micrometers. The results indicate possibilities to create a wealth of water-responsive structured CS films on solid surfaces.
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| 2. |
- Mokhtari, Tahereh, et al.
(författare)
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Controlling interfacial film formation in mixed polymer-surfactant systems by changing the vapor phase.
- 2014
-
Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 30:33, s. 9991-10001
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Tidskriftsartikel (refereegranskat)abstract
- Here we show that transport-generated phase separation at the air-liquid interface in systems containing self-assembling amphiphilic molecules and polymers can be controlled by the relative humidity (RH) of the air. We also show that our observations can be described quantitatively with a theoretical model describing interfacial phase separation in a water gradient that we published previously. These phenomena arises from the fact that the water chemical potential corresponding to the ambient RH will, in general, not match the water chemical potential in the open aqueous solution. This implies nonequilibrium conditions at the air-water interface, which in turn can have consequences on the molecular organization in this layer. The experimental setup is such that we can control the boundary conditions in RH and thereby verify the predictions from the theoretical model. The polymer-surfactant systems studied here are composed of polyethylenimine (PEI) and hexadecyltrimethylammonium bromide (CTAB) or didecyldimethylammonium bromide (DDAB). Grazing-incidence small-angle X-ray scattering results show that interfacial phases with hexagonal or lamellar structure form at the interface of dilute polymer-surfactant micellar solutions. From spectroscopic ellipsometry data we conclude that variations in RH can be used to control the growth of micrometer-thick interfacial films and that reducing RH leads to thicker films. For the CTAB-PEI system, we compare the phase behavior of the interfacial phase to the equilibrium bulk phase behavior. The interfacial film resembles the bulk phases formed at high surfactant to polymer ratio and reduced water contents, and this can be used to predict the composition of interfacial phase. We also show that convection in the vapor phase strongly reduces film formation, likely due to reduction of the unstirred layer, where diffusive transport is dominating.
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