Corporate Research
Modelling reality
Polymer chemistry dictates much of what is going on at DPI. It is important to know how a material is made, but it is just as important to know why it behaves the way it does. Models play a very important role in this field.
During the four years that Tim Mulder worked in the Corporate Research technology area he tried to unravel the mechanical behaviour of amorphous glassy polymers. Mulder: "Some polymers are brittle, some are ductile and some can be either brittle or ductile, depending on their history. We tried to understand this behaviour at the molecular level with the ultimate goal of being able to develop new materials with excellent properties. Experiments in this field are very expensive and have so far failed to bring the desired insight, so we used molecular and rheological modelling.
However, modelling also has its limitations, which are related to the extremely wide ranges of length and time scales that are important to polymer behaviour. With the help of an algorithm that Professor Doros Theodorou of the University of Athens developed ten years ago, and with methods such as coarse graining and scale jumping, we were able to greatly improve upon earlier simulations of commonly used polymers such as polystyrene and we could make a step towards understanding the mechanical behaviour of glassy polymers."
Professor Theodorou has been working in this field for a long time and was made aware of DPI via contacts he had at DSM and at the Eindhoven University of Technology (Netherlands). Theodorou: " What I appreciate most about DPI is that it is a very creative and lively polymer research community comprising both industrial and academic researchers. It is an excellent source of inspiration for new research programmes and provides opportunities for very vigorous scientific interaction. I submitted two proposals and both were granted. In my home country there is nothing comparable to DPI. As far as I know, the possibilities for close interaction between industry and academia that DPI offers are unique in the world."
Multi-scale
Even in the Corporate Research technology area, where members are mostly of academic origin, the influence of industrial people is important. Theodorou is very positive about it: "There have been people who, looking at the work that we do, were able to find ways in which this work could be useful for solving their very practical materials design and optimization problems. That is something I could not do myself. I'm quite impressed by the knowledge, judgement and resourcefulness of these people.
" In the academic world molecular models tell you everything about processes taking place at length scales of tens of nanometres and time scales of microseconds. The challenge for Theodorou is to bridge the gap to the industrial world and predict what happens at time scales of hours and length scales of metres. Multi-scale modelling it is called and according to Theodorou it is made possible not only by the advances in computer hardware but certainly also because new insights and algorithms have been developed. In his current DPI project he is investigating how cavities emerge in rubbery polymers subjected to tensile stress.
Mulder defended his thesis earlier this year and now works for Océ-Technologies, the Dutch printer and copier company, in a completely different field: image processing. Yet the experience he has gained with rheological models helps him to choose useful strategies for tackling image processing problems. "By analyzing and manipulating images we attempt to obtain optimal results in terms of print quality and image productivity, given the hardware limitations of a printer, or we correct or mask errors in printers.
A well-known example is the appearance of white lines when you use the fast print mode of a standard inkjet printer. But is not only the technical experience of DPI that I use in my new job. I have also experienced the value of a good competence network. DPI is very successful, via a multitude of ways, at achieving synergy by bringing the right people into contact with each other. It is through DPI that I came into contact with all the people who are relevant to my project."
Tim Mulder studied the behaviour of polymer glasses and its relationship with polymer properties in his PhD project at Eindhoven University of Technology in the Netherlands. He now works at Océ-Technologies and investigates strategies to tackle image processing problems.
Professor Doros Theodorou did his PhD project at MIT, was Professor of Chemical Engineering at the University of California, Berkeley (USA), and is now Professor at the National Technical University of Athens (Greece). He has two DPI projects related to modelling of materials and is very interested in the possibilities offered by DPI.
Polymer characterization
The preparation of tough heterogeneous systems based on amorphous polymers is focussed on changing the deformation mechanism from crazing to shear yielding. This, in combination with cavitation for delocalisation of the strain, can be achieved by decreasing the morphology size such that the interparticle local thickness becomes too small to allow for craze formation. For a minimum loss in modulus and strength the size of the rubber morphology has to be decreased to below 1 micrometer. Several successful systems have been developed.
The change in mode of microscopic deformation has been studied by time-resolved X-ray scattering during mechanical testing using synchrotron radiation at the Dutch-Belgian Beamline (DUBBLE) at ESRF, Grenoble, France. At this SAXS/WAXS station, several sample environments, such tensile tester, pressure cells, rheometers, and heating devices, can be inserted. Simultaneously, wide- and small-angle scattering patterns can be obtained with a time-resolution of seconds probing structures of polymers from 1-1000 Å.
