In collaboration with G. Auernhammer and H.-J. Butt, Physics at Interface Group, MPIP, Mainz, Germany

What can happen if you load a common colloidal suspension in a chamber, let it overnight, go home and come back next day to observe it? Not much, you would probably guess...but look more carefully at the air/water interface: you might observe beautiful crystals!

Directed Organization of Microparticles at Fluid Interfaces

We are exploring two aspects of the spontaneous 2D colloidal crystallization. On the one hand, we are interested in elucidating the physical mechanism behind this interfacial self-assembly process. On the other hand, we hope that the acquired knowledge will help us to control the process and ideally use it for the tailored particle patterning at fluid/fluid interfaces. This could ultimately lead to the development of new, complex and programmable two-dimensional materials.

Colloidal particles tend to spontaneously adsorb at the air/water interface of an aqueous colloidal suspension. A key parameter defining the affinity of the particles for the interface is their hydrophobicity.

Learning from the Coffee-Ring Effect, we are currently investigating the possibility of tuning post-synthesis particle affinity for a liquid/gas interface. Under specific physico-chemical conditions, the interplay of the interactions between adsorbed particles can be such that  particles spontaneously form two-dimensional, macroscopic (mm-sized) colloidal crystals. A confocal microscope image of such a 2D crystal made from 5 ┬Ám polystyrene particles is shown below.