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Igor Santos De Oliveira (promotion date: 7 December 2012)

Simulations of flow induced ordering in viscoelastic fluids

Promotion date: December 7.

Promotor: Prof. Wim Briels

Assistant promotor: Dr. ir. Wouter den Otter

Depending on the characteristics of the liquid, dispersion of colloids are observed to align in the direction of the flow forming string-like structures. Moreover, mixtures of bi-dispersed colloids also segregate by size. The colloidal structures remain stable only during the application of flow. This behavior is only found in some complex fluids, and the mechanism driving the colloids to the aligned configuration was not previously elucidated. This phenomenon has been subject of study for many years, due to its importance in many technological applications, as for example in the food and cosmetics industry.

In this thesis, coarse grained simulations are used to investigate the flow behavior of spherical colloids dispersed in shear-thinning viscoelastic fluids. The simulations are performed with the Responsive Particle Dynamics (RaPiD) method, developed in our group. We show that the method can simulate a large variety of complex fluids, by tuning only a few parameters. With the simulations we are able to obtain new insights and a better understanding of the colloids alignment. Besides that, colloid migration in confined systems was also investigated.

Was there a special moment during your thesis work that you recall very well?

Building a computational simulation model, identifying and controlling the parameters for describing these complex fluids, is a long term project. To notice that in our simulations we saw the same things predicted by experiments, was very rewarding. Step by step we could validate the models we developed and could coherently describe the special phenomena occurring here.

Simulation models can guide experimentalists a great deal, I believe, in this type of research. Some industrial applications are at stake here, for example to help control processes in food industry and in cosmetics in which the adding of small particles in complex fluids is a major topic.

Did you manage to submit some nice papers?

Two papers were published, in the Journal of Chemical Physics. Two articles are in preparation now, for different magazines. Also I was a speaker on the International Conference on Rheology, in Portugal last summer.

In what way did you grow yourself, as a scientist and researcher, during these four years?

Now I am much more confident to carry out a research project independently and apply modern scientific methods to complex phenomena like these. Communication is a key factor, I believe. As I was working on the computational simulations, especially the contacts to experimentalists were decisive. The results should lead to reasonable experiments that are able to shed a new light on the phenomena. These could lead to a true development of research in this field. Especially the nice contacts to the colleagues of the Catholic University Leuven were of significance here.

What are your future plans?

I am planning to stay one more year here, working in a post-doc position to further develop my research skills in a related project. At some point I would like to return to Brazil and perhaps start working at one of the renowned universities or institutes Brazil has to offer, favourably at a department of physics or chemistry at the University of São Paulo as they possess one of the best universities in Latin America.

What, in your opinion, is important for Mesa+ to stay successful in future?

Mesa+ is a well-known institute all over the world, as I experienced quite often so. The facilities are great. Of course human resources are equally important, no matter if professors, technicians, post-docs and PhD-students are meant. In Brazil a lot of good students are there - I am sure of - who are willing to travel abroad and join the great research projects here in Holland. Also the Brazilian government is financially supporting the talented students to go and broaden their knowledge and skills abroad. Mesa+ could be successful in advertising for talent in Brazil.