Part II projects

In our group we study colloidal suspensions, where particles on the order of a micrometer (the colloids) are dispersed in a solvent. Colloidal systems are highly interesting and relevant, as they find numerous applications in several industrial branches such as coatings, food, cosmetics but also in more technical applications as photonic crystals and data storage devices. In addition, colloids are widely accepted as a versatile model system for atoms and molecules as their phase behaviour is analogous to that of atomic and molecular systems; they display rich phase behaviour involving colloidal  ‘crystal’, ‘liquid’ and ‘gas’ phases. The typical colloidal length and time scales, i.e. micrometers and seconds, make it possible to directly observe colloidal particles in real-space and real-time using video- and/or confocal microscopy. Advanced colloid chemistry techniques are available to tune the chemical and physical properties of the particles or even to develop completely new and unique colloidal model systems. In addition, colloidal systems are easily deformed and manipulated using external fields such as optical laser tweezers.

Please find below some examples of possible part II research projects. If you are interested, please contact Roel Dullens for more detailed information. These projects will be carried out in close collaboration with the group of Dirk Aarts. Please click here to find out more about Part II projects in the Aarts group.

  1. Colloidal model systems
  2. Optical tweezers
  3. Grain boundaries and frustrated crystallisation
  4. Colloids in confinement
  5. Solid-fluid interfaces
  6. Contact Roel Dullens for the latest ideas!
  7. Edinburgh presentation

  • Synthesis and charaterisation of new colloidal model systems

core-shell PMMA rods
PMMA spheres polyhedral colloids

Well defined colloidal model systems are of upmost importance in the study of colloidal dispersions. Using colloid chemistry the chemical and physical properties of the colloidal model system can be precisely adjusted to the physical experiments in mind. Therefore, the synthesis and characterisation of colloidal model systems plays a central role in our research.A wide variety of chemical techniques is available to synthesize many different colloidal particles with very specific properties. For example, very monodisperse silica or latex spheres can be made, bit also rods, magnetic and fluorescent colloids can be prepared. Also the specific interactions between colloids can be controlled using surface chemistry. To characterise the particles several techniques such as light scattering, optical (confocal) microscopy and electron microscopy will be used.

Further reading:

  • Optical Tweezers

An optical tweezer is a strongly focussed laser beam that can trap small objects, such as colloids, using the forces that are exerted by the light. The scattering forces push the particles down and the gradient forces pull the particle towards the center of the beam. Combining optical tweezers and colloidal systems facilitates the ability to control, manipulate and deform colloidal systems on the microscopic, i.e. single-particle level (see MOVIE on the right!).

Further reading:
  • D. G. Grier, Nature 424, 810 (2003)
  • D. L. J. Vossen et al, Rev. Sci. Instrum. 78, 2960 (2004)
  • M. J. Lang, S. M. Block, Am. J. Phys. 71, 201 (2003)

laser trapping

  • Grain boundaries and frustrated crystallisation

The strength of materials is closely related to the grain size of the material. However, grain boundary stability is still far from understood. Using geometrical frustration, crystals which are rich in grain boundaries can be prepared. By studying the structural and dynamical behaviour of both colloidal single crystals and crystal imperfections insight will be gained into the relation between frustration and the stability of grain boundaries.

Further reading:

  • Colloids in confinement

The behaviour of colloids can be significantly affected by confinement. Well-defined confining geometries will be developed and we plan to study the influence of confinement on the formation and structure of colloidal (hard sphere) crystals. Futhermore, we want to look into the dynamics of concentrated colloidal suspensions in confinement and glass formation in such systems. This work is done in collaboration with Volkert de Villeneuve and Dirk Aarts

Further reading:

  • Solid-fluid interfaces

Suspensions of hard-sphere colloids display an entropy-driven fluid-crystal transition. This remarkable phenomenon widely serves as a simple model of crystallization in atomic systems. Detailed knowledge of the structure and dynamics of the solid-fluid interface is of central importance for processes such as crystal nucleation and growth. Using specially developed ‘core-shell’ colloidal hard spheres and confocal microscopy the equilibrium and non-equilibrium properties of the interface can be studied at the single particle, model atomic level.

Further reading: