Hartmut Löwen: soft condensed matter and more

By Jade Holt on August 21, 2015

We interview Professor Dr Hartmut Löwen of the Heinrich-Heine-Universität Düsseldorf. A theoretical physicist, who obtained his PhD in 1987 and has over 300 published articles, talks here about his research in soft condensed matter and what keeps him motivated in this fast paced field of physics.

Q: What research projects are you and your group currently working on?
For decades I have been working in the field of theoretical soft condensed matter physics. Soft matter is typically composed of mesoscopic particles, which have a structural length scale between a nanometer and a micron. They usually comprise of colloidal suspensions, polymers, liquid crystals, membranes and also biological matter, such as protein and DNA solutions. My group is working in theoretical physics using methods such as density functional theory, scaling theory and mode coupling theory, but we are also pursuing computer simulations of model systems. It is one of the characteristics of soft matter research that much of the progress happens in collaboration between experiment and theory. My current research projects concern phase behaviour of colloidal suspensions, the modelling of microswimmers, ferrogels and liquid crystals, and finally the link between colloids and complex (dusty) plasmas.

Q: What motivated you to pursue this field of research?
As already mentioned, a close collaboration with experimentalists is typical for this field of research. Here, a theory is not just pure imagination, which remains untested for decades, but can be directly verified or disproved by experiments. This results in a strong cross-fertilization between experimental and theoretical groups, often resulting in many joint publications. This feature is not so obvious in many other fields of physics, to mention high energy physics, for example. This is exciting, in particular as a theoretician, as one can motivate and influence new experiments of the next day. Another motivation is that on the mesosocopic scale many constituents can be tailored almost at wish, such that simple models of classical physics can be realized. This gives rise to a plethora of new models to be explored, which are simple enough such that young students have the option to start research on their own model. This means they are not just a wheel in a big machine, but can produce scientific output on their own, even at a pretty early stage of their career.

Q: Where do you think the field is heading?
I would like to mention three main topics, in which research streams of soft matter physics are outflowing.

A pretty new development is the motion of bacteria and artificial colloids (so-called microswimmers).
This is a field where statistical physics, hydrodynamics and biology meet. It was recently explored not by biologists, but by physicists and biological physicists. Much of my work is published in this field, such as B ten Hagen et al 2011 J. Phys.: Condens. Matter 23 194119, which moves at an extremely high pace.

A second research line concerns smart materials with “intelligent” properties, which can be tuned e.g. by external stimuli. One important example are ferrogels, i.e. a combination of ferromagnetic mesoscopic particles embedded in a gel that can be addressed by magnetic fields and possesses largely adjustable elastic properties, but there are many other examples. For these systems, new theories are needed which employ the concept of coarse-graining, a concept of classical statistical mechanics, since several different length scales are involved.

Thirdly, understanding and classifying non-equilibrium phenomena is a nontrivial task. This is an old problem dating back to Boltzmann or even earlier, where progress is sparse since the problem is so hard. In this respect colloids are an ideal model system where non-equilibrium phenomena can be studied at the particle scale. This has been an important research topic of the past two decades.

Q: Who inspired you to become a scientist?

It was not a particular person. When I was 18 years old, I was participating in an Olympic-style tournament for physics where international teams had to solve exercises. Some of these exercises lead to the solution of novel problems. I was curious to solve new problems and also be in competition with others. That curiosity was the main driving force for me to get interested in science, and in particular physics.

Q: What do you find to be the most rewarding aspect of your job?
In fact there are three main aspects:

In my job I work with young people (students, PhD students, postdocs), this keeps me young!
A significant fraction of my time is consumed with traveling all over the globe, since science is international. I like the opportunity to see new corners of our planet.
There is a large freedom in my job as far as my research topic is concerned, which is of high value. By the way, it is not the salary. One can get more money elsewhere, but money is not all in life.

Q: What advice would give to young scientists?
Firstly, it is very important for a career in science to select a strong research group, which is linked internationally and has international recognition. This, in my opinion, is more important than the name and reputation of the University.

You can read more on Hartmut Löwen’s work, here.

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