Nikodem Tomczak (promotion date: 18 May 2005)

Single light emitters in the confinement of polymers

Promotion Date: 18 May 2005

What was your thesis about?

The main objective of my PhD research was to develop new experimental methods based on single molecule fluorescence detection and spectroscopy to probe polymers on the nanoscale. In particular, my research was concentrated on polymer dynamics in confinement such as in thin films (used often in such areas as standard lithography). Additionally, we were also studying the effects structures with dimensions smaller than the wavelength of light have on the photophysical properties of the emitters.

Where do the light emitters come in?

Our probes were molecules that are able to emit light, fluorescent molecules. By mixing the fluorescent molecules with the polymers, and by looking at the photons emitted by a single molecule embedded in the polymer it is possible to tell something about the dynamics of the surroundings of the probe. In the case of polymers where there is a large degree of mobility present one can follow the rotational or translational diffusion processes at the single probe level. When the polymer is too rigid for long range diffusion processes to occur on an experimental time scale one is still able to obtain the information on the local polymer dynamics by looking at the subtle changes in the emission characteristics of the molecules (for example by monitoring the fluorescence lifetime).

With what aim?

Although there are methods, which probe polymers on the nanoscale they all lack the combination of high spatial resolution with nonensemble information. The aim was to develop new experimental methods based on single molecule optical detection, which combine the above-mentioned requirements and use them to answer some questions regarding e.g. polymer segmental dynamics in thin films.

Since thin films are so often used in nanotechnology your research must have been vital.

The newly developed methods were applied to look at the dynamics of polymers when confined into thin films. By decreasing the thickness of the films, we could see the consequences of the confinement on the polymer segmental mobility. We have shown that the dynamics in thin polymer films can be already affected throughout the films when confining the polymers to a thickness much larger than the polymer size, even at temperatures far below the polymer glass transition temperature.

And is your work conclusive for that?

We were working on a model polymer – polystyrene. There is still work to be done with other polymer systems and see whether the conclusions of our work can be generalized for other polymers. One PhD research is definitely too short.

Are you a physicist?

No, I am a chemical engineer.

How come a chemical engineer gets his doctoral degree on a physics subject?

It started a long time ago when I came here to Twente (I am from Poland, Gdansk) for a summer stay. I was involved in a project of one of the PhD’s (Jason Pickering). Among other things, he was working on the measurement of adhesion properties of polymers on the nanoscale. I found it interesting and when a project came up combining polymer nanoscale properties and optics, single molecules and physics, I jumped at the opportunity. It was a challenge and it also had a kind of charm.

You worked here in two groups?

Yes, in the Materials Science and Technology of Polymers group (Prof. Julius Vancso) and in the Applied Optics group (Prof. Niek van Hulst). I did the sample preparation and related practical work in the Polymer group and the experiments were performed at the Applied Optics group. Working in two groups was challenging but it really worked well. Additionally, working in two different scientific environments opened up perspectives for new research.

Where are you from?

I am form Poland, from Gdansk.

For the summary of the thesis, click here.