Time- and Space-Resolved SAXS Experiments Inform on Phase Transition Kinetics in Hydrated, Liquid-Crystalline Films of Polyion–Surfactant Ion 'Complex Salts'
| Autor: | Lennart Piculell, Joaquim Li, Charlotte Gustavsson |
|---|---|
| Rok vydání: | 2016 |
| Předmět: |
Phase transition
Small-angle X-ray scattering Chemistry Kinetics Analytical chemistry Hexagonal phase 02 engineering and technology Surfaces and Interfaces 010402 general chemistry 021001 nanoscience & nanotechnology Condensed Matter Physics 01 natural sciences 0104 chemical sciences Ion Crystallography Pulmonary surfactant Phase (matter) Electrochemistry Micellar cubic General Materials Science 0210 nano-technology Spectroscopy |
| Zdroj: | Langmuir. 32:5102-5110 |
| ISSN: | 1520-5827 0743-7463 |
| Popis: | Detailed time- and space-resolved SAXS experiments show the variation with hydration of liquid crystalline structures in ethanol-cast 5-80 μm thick films of polyion-surfactant ion "complex salts" (CS). The CS were dodecyl- (C12) or hexadecyl- (C16) trimethylammonium surfactants with polyacrylate (DP 25 or 6000) counter-polyions. The experiments were carried out on vertical films in humid air above a movable water bath, so that gradients of hydration were generated, which could rapidly be altered. Scans over different positions along a film, kept fixed relative to the bath, showed that the surfactant aggregates of the various liquid-crystalline CS structures grow in cross-sectional area with decreasing hydration. This behavior is attributed to the low water content. Studies of films undergoing rapid dehydration, made possible by the original experimental setup, gave strong evidence that some of the investigated systems remain kinetically trapped for minutes in a nonequilibrium Pm3n micellar cubic phase before switching to the equilibrium P6mm 2D hexagonal phase. Both the length of the polyion and the length of the surfactant hydrocarbon "tail" affect the kinetics of the phase transition. The slowness of the cubic-to-hexagonal structural transition is attributed to the fact that it requires major rearrangements of the polyions and surfactant ions relative to each other. By contrast, other structure changes, such as between the hexagonal and rectangular phases, were observed to occur much more rapidly. |
| Databáze: | OpenAIRE |
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