Research
Diffusion and flow in interacting complex fluids
For a spherical particle being pulled through a simple fluid (such as water) by an external force, the Stokes law governs the relation between the applied force and the particle velocity. However, when we consider a complex fluid, such as the cytoplasm of a cell, the Stokes law does not apply because of the multiple length scales involved due to the many constituents of the fluid. One change compared to simple fluids is that the viscosity becomes a wavevector-dependent quantity. In this particular project we investigate the effects of interactions of a probe particle with its environment, and how this shows up in viscous properties of the medium.
Ion-doped liquid crystals
Ions are often seen as an impurity in liquid-crystal systems, however, we want them! They can redistribute in very complex ways according to the local director field, flexoelectric polarisation and scalar order parameter distribution. In the schematic illustration this is shown for a half-integer wedge disclination loop.
Electrostatics of complex-shaped charged particles
The electric double layer around a charged colloidal particle can have interesting geometrical and maybe even topological properties. In the above figure we show how (a) a trefoil knot with different surface functionality within the particle can give rise to (b) highly inhomogeneous surface charge distributions, and (c) a complex geometrical and topological structure of the screening cloud around it.Â
In this research line we investigate how the electrostatics of particles with a non-trivial shape affects the effective pair interactions, phase behaviour and transport properties of these particles. The particles do not need to be colloidal, they can also be macromolecules such as DNA.
Medium and many-body effects in charged colloidal suspensions
Charged colloidal suspensions are influenced by the medium and by many-body effects. An example of a medium effect is, for example, shown in the left panel, where we see how a negatively charged oil-dispersed colloidal sphere gets stripped off its screening cloud when approaching a water phase (z<0). The stripped screening cloud affects the back-to-back double layer that is formed at the oil-water interface because ions dissolve better in water than in oil.
An example of a many-body effect in charged colloidal suspensions is, for example, that charge-regulating particles discharge when we make the suspension denser. This discharging gives rise to the phase diagram in the right panel for colloidal spheres. If also negative ions can adsorb on the particle besides positive ions (innermost lobes), we see that the phase diagram changes such that a density-induced reentrant BCC phase emerges.