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Contact angles of microellipsoids at fluid interfaces.
Stijn Coertjens1, Paula Moldenaers, Jan Vermant
1Department of Chemical Engineering, KU Leuven , B-3001 Leuven, Belgium.
Langmuir : the ACS Journal of Surfaces and Colloids
|April 12, 2014
Summary
Wetting of anisotropic particles depends on shape and surface chemistry. A new method reveals contact angle variations, challenging ideal models and highlighting line tension effects for higher aspect ratios.
Area of Science:
- Colloid and surface science
- Materials science
- Interfacial phenomena
Background:
- Wetting of anisotropic particles is crucial for Pickering emulsions and foams.
- Previous studies lacked methods to analyze individual anisotropic particles' wetting behavior.
- The combined influence of shape and surface chemistry on contact angles was poorly understood.
Purpose of the Study:
- Investigate contact angle variations of prolate ellipsoidal colloids at liquid-liquid interfaces.
- Analyze the impact of particle aspect ratio and surface chemistry on wetting.
- Extend freeze-fracture shadow-casting cryo-scanning electron microscopy (cryo-SEM) for ellipsoidal particle analysis.
Main Methods:
- Utilized freeze-fracture shadow-casting cryo-SEM to analyze individual prolate ellipsoidal colloids.
- Prepared ellipsoidal particles from polystyrene and poly(methyl methacrylate) spheres via film stretching.
- Investigated the effects of particle preparation protocols and cleaning steps.
Main Results:
- Observed wrinkling of the three-phase contact line with insufficient particle cleaning.
- Found that the cosine of the contact angle decreases linearly with increasing contact line length (aspect ratio).
- This trend deviates from Young-Laplace's equation, indicating significant line tension effects.
Conclusions:
- Developed and applied a cryo-SEM technique for analyzing anisotropic particle wetting.
- Identified an effective line tension contribution, influenced by surface heterogeneities.
- Higher aspect ratio ellipsoids show increased importance of line effects over surface effects in wetting behavior.
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