News

Marjolein Dijkstra new Scientific Director Debye Institute

On 26 January 2015, Prof. Marjolein Dijkstra was appointed Scientific Director of the Debye Institute for Nanomaterials Science by dean Gerrit van Meer. With this appointment, Prof. Marjolein Dijkstra succeeds Prof. Krijn de Jong, who was Scientific Director for the past 3 years. The appointment is for the period February 1, 2015 to February 1, 2018.

The Debye Institute is an interdisciplinary research institute that involves participation of the groups from Chemistry and Physics. The Scientific Director is alternately from each of the concerned departments.
The Scientific Director is responsible for the strategy, content and implementation of the program and for monitoring the quality of the research.

March 22nd, 2011: PhD Defense of Peter van Oostrum

Using Light Scattering to Track, Characterize and Manipulate Colloids

Colloidal particles are about as large as the wavelength of light. The scattering of light by these particles is a rich and interesting phenomenon. During my PhD I have used the scattering of light by colloids in various ways. First of all I co-developed a new method to analyze in-line holographic micrographs. Our particles are illuminated with a collimated laser beam. Part of the light is scattered and interferes with the remaining, not-scattered, light. This interference pattern is called a hologram. By combining Mie theory and the well known interference, it is possible to calculate holograms. We minimize the difference between an experimental hologram and a calculated hologram. Doing so, we can determine the particle's lateral position to within 1 nm, and, more interestingly to within 10 nm in the axial direction, from a single snapshot. Using a fast CCD camera it is then possible to track colloids in space with unprecedented accuracy and speed. This fitting procedure also gives the radius and the refractive index of the individual particle to about 1 %.

The same scattering behaviour that we use to track and characterize the colloids can be used to exert forces on them using optical tweezers. I performed extensive calculations of the forces exerted by optical tweezers on various colloids, including colloids with a core-shell structure. We used optical traps to measure colloidal forces between PMMA particles in CHC. A more sensitive measurement can be achieved when the particles diffuse freely while they move under influence of interaction forces between them. From the statistics of many holographically measured trajectories one can measure the interaction forces between the colloids with fN accuracy. We demonstrated that this technique allows measuring the screened charge interaction between colloids in various solvents.

January 2011: Synthesis of monodisperse silica rods

Synthesis of monodisperse, rodlike silica colloids with tunable aspect ratio
A. Kuijk, A. van Blaaderen, and A. Imhof, Journal of the American Chemical Society, Article ASAP (2011).

We have succeeded in synthesizing colloidal silica rods that spontaneously form a smectic phase. These particles can be viewed in 3D with a confocal microscope enabling studies of the phase behaviour and dynamics of concentrated suspensions of rodlike particles.

 
(Left) Transmission electron micrograph of the silica rods. (Center) Confocal micrograph of an aligned phase of fluorescent silica rods. (Right) Scanning electron micrograph of a dried smectic of silica rods.

30-6-2009: Publication in PNAS:

Melting and crystallization of colloidal hard-sphere suspensions under shear
Y. L. Wu, D. Derks, A. van Blaaderen, and A. Imhof, Proceedings of the National Academy of Sciences 106, 10564-10569 (2009).

Observations were made of a concentrated suspension of colloids undergoing shear. This is made possible by an advanced, home-built shear cell placed on a confocal microscope. A low shear rates we find that the order among the particles will gradually increase until a colloidal crystal is formed. At higher shear rates the crystal will shear melt again. However, the order shows very large fluctuations. Apparently, the crystal is never completely melted, but ordered domains keep appearing now and then.

(Left) Confocal microscopy images of an initially crystalline suspension of 1.2 mm diameter silica particles taken at different times after it was set to shear with a rate of 2 s^-1.
(Right) The order parameter versus time and shear rate.

11-2-2007: Towards a photonic band gap for visible light

A.-P. Hynninen, J. H. J. Thijssen, E. C. M. Vermolen, M. Dijkstra, and A. van Blaaderen, Nature Materials (2007).

We have discovered a route by which crystals having a complete photonic band gap in the visible could be self-assembled from colloids. It makes use of the MgCu₂ Laves phase, which consists of two sublattices, each of which can be used to make a photonic crystal after selective removal of the other:

Computer simulations show that the desired binary crystal should grow on a wall that carries a cleverly designed regular pattern:

A more detailed account can be found in our press release: English or Dutch.
It can also be found on the FOM website.

Also read the News&Views article on this topic by D. J. Norris.

18-07-2006: Thermally excited capillary waves are suppressed by shear flow

by Didi Derks, Dirk Aarts, Daniel Bonn, Henk Lekkerkerker, and Arnout Imhof.
See the Physical Review Letters issue of 21 July 2006.

A FOM press release explains our findings in non-scientific Dutch.

08-03-2006: Prediction and observation of crystal structures of oppositely charged colloids

A.-P. Hynninen, C.G. Christova, R. van Roij, A. van Blaaderen, and M. Dijkstra, accepted in  Physical Review Letters (2006)

06-12-2005: Antti-Pekka Hynninen received his doctorate cum laude.
Title of his thesis: Phase behavior of charged colloids and the effect of external fields.

08-09-2005: SCM group publishes an article in Nature on "Ionic colloidal crystals of oppositely charged particles"

Please read the full story in our press release
"Gewone en exotische zouten maken met colloïden" (in Dutch)
or
"Making common and exotic salts with colloids" (in English)
or read
The news item on the Noorderlicht website (in Dutch)
The news item on PhysicsWeb (in English)

05-07-2005: SCM group is awarded a prestigious TOP grant by the Netherlands Organisation for Scientific Research (NWO).
Subject of the proposal: Ionic colloidal crystals.

Please read the NWO press release (in Dutch).

8-04-2005: Phase diagram of dipolar hard and soft spheres:Manipulation of colloidal crystal structures by an external field, Antti-Pekka Hynninen and Marjolein Dijkstra, Physical Review Letters 94, 138303 (2005)

Please read the press release by FOM.

22-11-2004: Dirk Vossen earns his doctorate cum laude !
Title of his thesis: "Optical tweezers in concentrated colloidal dispersions".

30-6-2004: UU awards High Potentials subsidy to Marjolein Dijkstra, René van Roij and Arnout Imhof !

Please read the press release by Utrecht University.

30-1-2003: A colloidal model system with tunable interactions

Read more in AMOLF highlights (in English), Persbericht (in Dutch), or Bild der Wissenschaft (in German).

Click here for a cool picture!

13-01-2003: Epitaxial growth of charged colloids

J. P. Hoogenboom, A. Yethiraj, A. K. van Langen-Suurling, J. Romijn, and A. van Blaaderen, Physical Review Letters 89, 256104 (2002).

Click here for a cool picture!

05-04-2002: A new way to build binary colloidal crystals

A press release can be found here (in Dutch).

18-03-2002: Krassimir Velikov defends his thesis

And successfully, too! Krassimir now has his PhD.
The title of his thesis is "Towards a Complete Photonic Band Gap in the visible".

11-06-2001: Soft Condensed Matter Online

Our easy-to-remember web address: www.colloid.nl

29-03-2001: Poster prijs Peter Vergeer

29-03-2001: Oratie Alfons van Blaaderen:
Het geheim van de slimme schokdemper en elektronische inkt

Klik hier voor het nieuwsbericht

20-04-2000: Minerva Prijs Marjolein Dijkstra
Prijswinnares tegen de verdrukking in

Klik hier voor de tekst