Phd in the Spotlight: Sietse van der Post
Sietse van der Post (b. 1981) will be awarded his doctorate degree at the University of Amsterdam (UvA) on 7 February. His doctoral research at the Van 't Hoff Institute for Molecular Sciences (HIMS) focused on jumping water molecules.
What did you do?
'I studied the movements of water molecules with the help of a laser. It's been known for some time that water molecules move in tiny jumps, but it's not yet clear exactly what's happening at the molecular level. Water molecules are held together by hydrogen bonds. Whenever a molecule moves, at least one of those bonds has to be broken. These bonds are broken and formed through a sudden rotating movement.
Recently, it was discovered that water molecules don't move as fast when they are near water-repelling substances like fats. There's still considerable debate within the field about why this happens and to what degree. What we discovered is that it's probably due to the network of hydrogen bonds around these substances being more rigid. This effect disappears at higher temperatures.'
Why do you want to know how water molecules move?
'All life on earth is water-based; most organisms are more than 50% water. Though it would be going too far to say that if you understand water, you understand life, if you know how water molecules work, you'll know more about how cell walls are created, about why proteins assume a given structure and so on. So, in looking at cell membranes, which are made up of fats, we also wanted to observe water molecules in proximity to fatty substances.'
How do you measure the movement of water molecules?
'That is very complicated. A microscope can't see these molecules because they're extremely small – more than a thousand times smaller than the wavelength of visible light. What's more, they move very fast. If you wanted to film a water molecule in motion, you'd have to record more than a billion images per second.
Fortunately, we can measure these movements using a powerful laser that emits two pulses in quick succession. The first pulse excites a subset of the water molecules and the second measures the induced molecular changes. These changes provide information about how the water molecules move and how quickly they stop vibrating.'
What aspect of your research did you enjoy most?
'I enjoyed having so much freedom. My research was based at AMOLF, and I really had my very own project there. Whenever I got a new idea, I could just walk out from my office over to my lab 15 metres away and test it out. I didn't have to wait months on end for approval. Another nice aspect is that I was able to get results fairly quickly. Naturally, things didn't always go as smoothly, but on the whole the research went well. Even so, I'm going to leave academia now – to work in the research department at ASML, where the focus is more on applied science. I can't wait to start!'
