Capillary bridges on spheres

Symmetry breaking of capillary bridges on spheres

Chair: Physics of Complex Fluids

Imagine that one would be able to produce well-defined ‘colloidal molecules’ which are anisotropic colloidal particles that resemble the shape of molecules, such as ‘colloidal water’ or ‘colloidal ammonia’ (Fig 1a). These particles are expected to mimic molecular self-assembly through shape and directional interactions. Thus, they can be the building blocks for new materials with custom-made properties. To get the required functionality, one needs particles with a well-controlled non-spherical shape and tunable patchiness. This can be done by starting from cross-linked polymer particles with liquid protrusions, and subsequent coalescing and polymerizing of these protrusions to form a bridge [1].

Figure 1. (a) Colloidal molecules created from polymer particles (adapted from [1]), and a schematic representation of a water molecule. (b) Instability diagram indicating the occurrence of (a)symmetric liquid bridges. The different colors represent the separation distances between the two spheres.

We will use mm-sized spheres as a model system for the colloids, with a liquid bridge in between. The final shape of the ‘colloidal molecules’ depends on the separation of the spheres, and the ‘bond angle’. The latter can be tuned by the volume and the wettability of the liquid bridges (Figure 1b). The wettability can be expressed as the angle that the liquid makes with the sphere. By using electrowetting [2], we apply an electric field to the liquid to change this contact angle.

In this project, you will experimentally investigate the various symmetry-broken capillary bridges that can be obtained when changing the volume and contact angle reversibly (by using electrowetting). You will learn about capillarity and wetting, electrowetting, and energy considerations dictating morphological transitions.

[1] D. J. Kraft et al, JACS 131 (2009), 1182-1186

[2] Mugele and Baret, J. Phys.: Condens. Matter 17 (2005), R705-R774

supervision

e-mail

tel.

office

Tutor: Riëlle de Ruiter

Burak Eral, Jolet de Ruiter

r.deruiter-1@tnw.utwente.nl

3093

ME162

Teacher: Frieder Mugele

f.mugele@utwente.nl

3094

ME161