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Updated: Jun 2, 2026
09:26
Synthesis and Characterization of Supramolecular Colloids
Published on: April 22, 2016
Structure of colloidal sphere-plate mixtures
N Doshi1, G Cinacchi, J S van Duijneveldt
1School of Chemistry, University of Bristol, Bristol, UK.
Summary
Plate-like clay particles in coatings enhance sphere-like pigment dispersion at low concentrations but phase separate at higher concentrations. Dynamic arrest prevents large-scale separation in real paint films, maintaining opacity.
Area of Science:
- Colloid and surface science
- Materials science
- Rheology
Background:
- Coatings utilize spherical pigment particles and plate-like clay particles.
- Clay particles are believed to improve paint film opacity by spacing pigment particles effectively.
- This spacing effect is counterintuitive due to the tendency of dissimilar particle suspensions to phase separate.
Purpose of the Study:
- To investigate the behavior of mixed sphere-plate colloidal systems.
- To understand the role of particle shape and concentration on dispersion and phase separation.
- To clarify the mechanism behind the stable dispersion of particles in coatings.
Main Methods:
- A model colloidal system with a sphere-plate diameter ratio relevant to paints was studied.
- Small-angle neutron scattering was employed to analyze particle behavior in dilute suspensions.
- Theoretical predictions were used for comparison with experimental observations.
Main Results:
- In dilute suspensions, the addition of plates increased density fluctuations of spheres, aligning with theoretical predictions.
- At higher concentrations, spheres and plates phase separated due to shape disparity, consistent with depletion effects.
- No large-scale phase separation was observed in concentrated coatings.
Conclusions:
- The addition of plate-like particles influences sphere dispersion in colloidal systems.
- Phase separation occurs between spheres and plates at elevated concentrations.
- Dynamic arrest in concentrated, intimately mixed or micro-phase separated structures explains the lack of macroscopic phase separation in real coatings.
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