Periodic average structures of colloidal quasicrystals.

We experimentally study the phase behaviour of a charge-stabilized two-dimensional colloidal monolayer which is subjected to a one-dimensional quasiperiodic substrate potential. Upon increasing the laser intensity, we observe a transition from a periodic to a quasiperiodic state. It proceeds via the formation of an intermediate periodic average structure (PAS) which is related to the quasiperiodic lattice by a bounded 1-1 mapping.

Experimental observation of directional locking and dynamical ordering of colloidal monolayers driven across quasiperiodic substrates.

We experimentally investigate the structural behavior of an interacting colloidal monolayer being driven across a decagonal quasiperiodic potential landscape created by an optical interference pattern. When the direction of the driving force is varied, we observe the monolayer to be directionally locked on angles corresponding to the symmetry axes of the underlying potential. At such locking steps, we observe a dynamically ordered smectic phase in agreement with recent simulations.

Observation of kinks and antikinks in colloidal monolayers driven across ordered surfaces.

Friction between solids is responsible for many phenomena such as earthquakes, wear or crack propagation. Unlike macroscopic objects, which only touch locally owing to their surface roughness, spatially extended contacts form between atomically flat surfaces. They are described by the Frenkel-Kontorova model, which considers a monolayer of interacting particles on a periodic substrate potential.

Immersion of charged nanoparticles in a salt solution/air interface.

Electrostatic interactions strongly affect the immersion depth of nanoparticles into an interface. We prove this statement by measuring the diffusion constant of charged nanoparticles at a sodium chloride solution/air interface. Interfacial diffusion of nanoparticles slows down with increasing ionic strength of the sodium chloride solution.