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Re-entrant lamellar/onion transition with varying temperature under shear flow
Daijiro Sato1, Kahoru Obara, Youhei Kawabata
1Department of Chemistry, Tokyo Metropolitan University, 1-1 Minami-Osawa, Hachioji, Tokyo 192-0397, Japan.
Langmuir : the ACS Journal of Surfaces and Colloids
|December 11, 2012
Summary
Researchers discovered a novel reentrant lamellar-onion-lamellar transition in a surfactant system using simultaneous shear stress and small-angle X-ray scattering (Rheo-SAXS). This transition occurs with changing temperature under constant shear, revealing new insights into material phase behavior.
Area of Science:
- Materials Science
- Soft Matter Physics
- Physical Chemistry
Background:
- Surfactant systems exhibit complex phase behaviors, including lamellar and onion phases.
- Understanding phase transitions under external stimuli like shear is crucial for material applications.
Purpose of the Study:
- To investigate the reentrant lamellar-onion-lamellar transition in a nonionic surfactant/water system.
- To characterize the temperature and shear rate dependence of these transitions.
- To elucidate the changes in lamellar orientation during phase transitions.
Main Methods:
- Simultaneous measurements of shear stress and small-angle X-ray scattering (Rheo-SAXS).
- Utilized a nonionic surfactant (C14E5)/water system exhibiting a lamellar phase over a wide temperature range (15-75 °C).
- Investigated temperature dependence of lamellar repeat distance at rest.
Main Results:
- First observation of the reentrant lamellar-onion-lamellar transition under constant shear rate.
- The onion state exists within a closed region in the temperature-concentration diagram.
- Lamellar repeat distance increase with temperature is necessary for the lower transition.
- Detailed changes in lamellar orientation (velocity gradient to neutral direction) were observed during all transition processes.
Conclusions:
- The study reveals a novel phase transition pathway in surfactant systems under shear.
- Lamellar orientation changes are critical to understanding the lamellar-onion-lamellar transition.
- Findings contribute to the fundamental understanding of soft matter under flow conditions.
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