期刊
JOURNAL OF COLLOID AND INTERFACE SCIENCE
卷 561, 期 -, 页码 136-146出版社
ACADEMIC PRESS INC ELSEVIER SCIENCE
DOI: 10.1016/j.jcis.2019.11.092
关键词
Surfactants; Dissolution; Polarized light microscopy; Micro-Raman spectroscopy
Hypothesis: While the phase behavior of aqueous surfactant solutions is usually described in term of the equilibrium microstructures of lyotropic liquid crystals, the transformations which take place when a phase turns into another one, either by changing the concentration or the temperature, are still to be elucidated. A simultaneous determination of concentration and microstructure is at order to elucidate the phase behavior under changing conditions, such as in a dissolution experiment. Experiments: Confocal Raman micro-spectroscopy and time-lapse polarized light microscopy are combined to study the phase transitions taking place in the dissolution of a common anionic surfactant (sodium laurylethersulfate) in water. Findings: By comparing Raman concentration profiles and polarized light images, it is found that the aqueous solution, with initial surfactant concentration of 72 wt%, undergoes a sequence of complex microstructural transformations including distortion of the initial lamellar phase, formation of an intermediate striated texture, which can be considered as a precursor of a cubic phase, and a heterogeneous hexagonal phase going through a transition region before turning into a micellar phase. The effects of the sodium counter-ion and of water confinement are also investigated by analyzing the OH-stretching bands. (C) 2019 Elsevier Inc. All rights reserved.
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