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Autostratification in drying colloidal dispersions: experimental investigations
R E Trueman1, E Lago Domingues, S N Emmett
1Department of Chemical Engineering and Biotechnology, University of Cambridge, Pembroke Street, Cambridge CB2 3RA, United Kingdom.
Langmuir : the ACS Journal of Surfaces and Colloids
|January 20, 2012
Summary
This study investigates particle stratification in colloidal films, finding that diffusion drives layering but other flows are also important. Optimal stratification occurs with stable dispersions and specific Peclet numbers.
Area of Science:
- Materials Science
- Colloid Science
- Surface Science
Background:
- Understanding particle distribution in thin films is crucial for material properties.
- Previous models predict diffusional stratification in colloidal dispersions.
- Experimental validation of these models is needed.
Purpose of the Study:
- To experimentally investigate particle distribution normal to the substrate in films cast from two-particle-size colloidal dispersions.
- To compare experimental findings with a diffusional model.
- To identify conditions favoring particle stratification.
Main Methods:
- Casting thin films from colloidal dispersions with two distinct particle sizes.
- Utilizing atomic force microscopy (AFM) for surface topography and particle analysis.
- Employing Nuclear Magnetic Resonance (NMR) profiling for in-depth concentration analysis.
Main Results:
- Observed evidence of diffusion-driven particle stratification within the films.
- Highlighted the significant influence of other flow dynamics beyond diffusion.
- Identified key conditions enhancing stratification: stable dispersions, low initial volume fractions, low stratifying particle concentration, and Peclet numbers straddling unity.
Conclusions:
- Diffusional effects contribute to particle stratification in colloidal films.
- Non-diffusional flows play a critical role in the stratification process.
- Specific colloidal and flow conditions optimize particle layering for material applications.
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