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Haloing, flocculation, and bridging in colloid-nanoparticle suspensions
Everett N Scheer1, Kenneth S Schweizer
1Department of Chemical & Biomolecular Engineering, University of Illinois, 1304 West Green Street, Urbana, Illinois 61801, USA.
The Journal of Chemical Physics
|May 2, 2008
Summary
This study explores colloid-nanoparticle mixtures using integral equation theory. It reveals how particle size, charge, and attractions influence interactions, predicting distinct structures like nanoparticle haloing and bridging gels.
Area of Science:
- Colloid and Nanoparticle Science
- Soft Matter Physics
- Physical Chemistry
Background:
- Understanding the behavior of mixtures containing particles of vastly different sizes is crucial for designing advanced materials.
- Colloidal systems with nanoparticles exhibit complex phase behaviors and structural organization.
- Integral equation theory provides a powerful framework for studying equilibrium and nonequilibrium properties of such systems.
Purpose of the Study:
- To investigate the equilibrium structure of highly size-asymmetric mixtures of colloids and nanoparticles.
- To explore the influence of various parameters (size asymmetry, volume fraction, charge, interparticle attractions) on the potential of mean force (PMF).
- To qualitatively discuss nonequilibrium phenomena like aggregation and gel formation.
Main Methods:
- Employing integral equation theory with a hybrid closure approximation.
- Systematically varying parameters such as size asymmetry, nanoparticle volume fraction and charge, and attraction properties.
- Calculating the potential of mean force (PMF) between large spheres (colloids).
- Analyzing real and Fourier space mixture structure at nonzero colloid volume fractions.
Main Results:
- Predicted distinct forms of PMF: contact depletion attraction, nanoparticle haloing, and bridging minima.
- Demonstrated that increasing interfacial cohesion leads to deeper bridging minima.
- Showed that nanoparticle charging significantly alters the volume fractions for structural changes.
- Observed complex nanoparticle reorganization due to many-body correlations.
Conclusions:
- The interplay of size asymmetry, nanoparticle properties, and attractions dictates the emergent structures in colloid-nanoparticle mixtures.
- Repulsive barriers can arise at high nanoparticle fractions, offering kinetic stabilization.
- Theoretical predictions align with existing experimental and simulation findings, validating the model.
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