Dissolution of a surfactant-water lamellar phase investigated by combining time-lapse polarized light microscopy and confocal Raman spectroscopy
Authors: Capaccio A., Caserta S., Guido S., Rusciano G., Sasso A.
Autors Affiliation: Univ Napoli Federico II, Complesso Univ Monte S Angelo, Dipartimento Fis E Pancini, Via Cinthia, I-80126 Naples, Italy; Univ Napoli Federico II, Dipartimento Ingn Chim Mat & Prod Ind, Piazzale V Tecchio 80, I-80125 Naples, Italy; CNR, INO, Comprensorio Olivetti Via Campi Flegrei 34, I-80078 Pozzuoli, NA, Italy
Abstract: 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.
Journal/Review: JOURNAL OF COLLOID AND INTERFACE SCIENCE
Volume: 561 Pages from: 136 to: 146