Thesis subject
MSc - Colloidal cereals: Cluster formation of particles on liquid surfaces
There is an increasing interest in studying the behavior of colloidal particles at liquid-air and liquid-liquid interfaces. From a practical viewpoint, particle-covered surfaces play a crucial role in determining the stability of emulsions, foams and coatings.
At the same time, they are an ideal model system for studying some fundamental issues in colloid science and soft matter physics. Many questions about the interactions between particles on surfaces are still unresolved. When closely packed, charged particles tend to order in dense hexagonal patterns so that the electrostatic repulsion between the particles is minimized [1].
As the surface coverage is lowered, the particles usually move further apart and the ordering is lost. However, we recently observed that in some cases one can also observe ordered or disordered clusters at low particle densities, showing that there must be a long-ranged attraction between the particles. This attraction is due to surface tension forces that arise because the presence of the particles causes a deformation of the liquid surface.
This effect has been called the “cereal effect”, because the same phenomenon happens when you make your cereals for breakfast: the cereals floating on the surface of the milk cluster together in order to minimize the surface area. It also governs the behavior of bubbles on the surface of a soft drink. However, when and how exactly this force arises for small colloidal particles is still largely unknown. This project aims to unravel these questions by studying cluster formation on surfaces by confocal microscopy.
In this project you will study experimentally the interactions of particles on liquid surfaces. The research focuses on:
- Studying cluster formation of particles on surfaces
- Measuring the interaction potential between particles and studying how it depends on particle size and shape, salt concentration, surface tension, and surface curvature
Experimental techniques:
- Preparation of patterned hydrophobic/hydrophilic surfaces by PDMS stamping
- Confocal microscopy
- Particles tracking in MatLab
- Optionally: theoretical modeling of particle interactions
References:
1. Electric-field-induced capillary attraction between like-charged particles at liquid interfaces; M. G. Nikolaides, A. R. Bausch, M. F. Hsu, A. D. Dinsmore, M. P. Brenner, C. Gay & D. A. Weitz
2. Pleats in crystals on curved surfaces; William T. M. Irvine, Vincenzo Vitelli & Paul M. Chaikin
3. Curvature-induced capillary interaction of spherical particles at a liquid interface; Alois Wurger