Thesis subject

BSc & MSc - Colloids feel the squeeze: Colloidal crystals in confinement

Ordered structures of atoms and small molecules, known as crystals, form the basic materials that surround us in both nature and our man-made environment; think of metals and semiconductors, sugar and salt crystals and protein assemblies required for x-ray crystallography.

Left: Colloidal “Wigner” crystal in bulk with confocal microscopy and a computer-generated rendering of the 3D crystal structure. Right: SEM image of microfabricated microwells and a confocal microscopy image of the unexpected helical structure of strongly confined colloidal crystals.
Left: Colloidal “Wigner” crystal in bulk with confocal microscopy and a computer-generated rendering of the 3D crystal structure. Right: SEM image of microfabricated microwells and a confocal microscopy image of the unexpected helical structure of strongly confined colloidal crystals.

While being of immense importance, several key aspects of crystallization remain poorly understood. One of these cases is the unknown way in which confinement influences crystal structure; how does a crystal structure adjust to a geometry that is only a couple of atoms or molecules wide?

Answering this question is difficult, if not impossible, using atoms and molecules, for 2 reasons: i) creating a well-defined confining structure that is only a few atoms wide is very difficult experimentally and ii) the extremely small dimensions of the individual atoms makes direct visualization of the 3-dimensional structure impossible.

Interestingly, colloidal particles, typically between 100 nanometers and 10 micrometer large, show the same crystallization phenomena as atoms and molecules (see figure); we can thus use “colloids as big atoms”. In this project we will exploit the much larger size of colloids to study the fascinating effects of confinement on crystallization. Colloids can be directly visualized in 3 dimensions using confocal microscopy, while confinement geometries can now be scaled up to the many-micrometer regime. We will use high-tech lithography methods to create well-defined microwells (see figure) and explore the effects of their confining walls on the structure and dynamics of colloidal crystals. Your work will lead to the discovery of exciting new structures and new insight into the fundamental puzzle that is crystallization.

Experimental techniques:

  •     Confocal microscopy
  •     Microfabrication/clean-room techniques
  •     Digital image analysis methods (with ready-to-use MatLab codes)
  •     Computer-generated rendering of crystal structures
  •     Optional: colloid synthesis, development of image analysis code