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Sedimentation and phase transitions of colloidal gibbsite platelets
Judith E G J Wijnhoven1, Daniëlle D Van't Zand, David van der Beek
1Van't Hoff Laboratory for Physical and Colloid Chemistry, Debye Institute, Utrecht University, The Netherlands.
Langmuir : the ACS Journal of Surfaces and Colloids
|November 3, 2005
Summary
Particle size dictates colloidal behavior in gibbsite platelet suspensions. Larger particles initially sediment, while smaller ones rapidly form gels or separate into phases before sedimentation occurs.
Area of Science:
- Colloid Science
- Materials Science
- Physical Chemistry
Background:
- Colloidal suspensions exhibit complex phase behaviors.
- Gibbsite platelets are anisotropic particles with potential for ordered structures.
- Understanding competing processes like sedimentation and gelation is crucial for materials design.
Purpose of the Study:
- To investigate the interplay between sedimentation, gelation, and liquid crystal formation.
- To determine how particle size and ionic strength influence these competing processes.
- To map the macroscopic behavior of colloidal gibbsite platelets.
Main Methods:
- Suspensions of colloidal gibbsite platelets with varying sizes (210-570 nm) were studied.
- Experiments were conducted at three different ionic strengths.
- Macroscopic behavior was observed over time, considering sedimentation and phase transitions.
Main Results:
- For larger platelets (350-570 nm), sedimentation dominates initially, followed by phase separation.
- For smaller platelets (210-270 nm), rapid gelation or phase separation occurs first, then sedimentation dictates the final state.
- Six distinct macroscopic scenarios were identified based on particle size and ionic strength.
Conclusions:
- The competition between sedimentation and ordering (gelation/liquid crystal formation) is strongly dependent on particle size.
- A two-fold scheme describes the observed behaviors, influenced by initial particle dynamics.
- These findings align with the established phase diagram for colloidal gibbsite platelets.
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