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Microstructure of Sodium Montmorillonite Gels with Long Aging Time Scale
Yee-Kwong Leong, Mingyong Du, Pek-Ing Au1
1Department of Chemical Engineering , Curtin University , Miri , Sarawak , Malaysia , 98009.
Langmuir : the ACS Journal of Surfaces and Colloids
|July 29, 2018
Summary
Sodium montmorillonite (SWy-2) gels exhibit significant time-dependent rheological aging, characterized by increasing yield stress over extended rest periods. This aging is linked to the formation of a unique cellular microstructure driven by inter-platelet forces.
Area of Science:
- Rheology
- Materials Science
- Colloid Science
Background:
- Sodium montmorillonite (SWy-2) gels are known to exhibit complex rheological properties.
- Understanding the time-dependent behavior (aging) of these gels is crucial for various applications.
Purpose of the Study:
- To investigate the long-term aging behavior of purified sodium montmorillonite (SWy-2) gels.
- To characterize the microstructure formed during the aging process.
- To elucidate the mechanisms driving the observed rheological changes.
Main Methods:
- Rheological measurements to quantify yield stress over time.
- Cryogenic scanning electron microscopy (cryo-SEM) under high pressure to visualize microstructure.
- Analysis of inter-platelet forces and platelet properties.
Main Results:
- Gels showed pronounced aging, with yield stress increasing over a week of rest.
- A sponge-like cellular microstructure with sub-micrometer openings was observed in aged gels.
- Aging is attributed to extensive bond formation and platelet adjustments in response to inter-platelet forces.
Conclusions:
- The observed aging behavior and cellular microstructure are governed by attractive and repulsive forces between montmorillonite platelets.
- Platelet shape, charge, and continuous force adjustments contribute to the long aging timescale.
- The repulsive force plays a key role in regulating the development of the microstructure towards a state of lowest free energy.
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