A new method has allowed realistic simulation of complex fluids for the first time. With the “coarse graining” method, physicists from Forschungszentrum Juelich, the University of Vienna, the University of Rome, and the Institut Laue-Langevin used spheres (on the right) to replace the complex macromolecules of the mixture of star polymers (yellow and blue) and linear polymers (red) shown on the left. They integrated the eliminated information as averages into the simplified system so that the characteristics of the substances were retained. Neutron scattering experiments were used to demonstrate the success of the method. Credit: Forschungszentrum Juelich/University of Vienna
international research team has successfully developed a widely
applicable method for discovering the physical foundations of complex
fluids for the first time. Researchers at the University of Vienna and
University of Rome have developed a microscopic theory that describes
the interactions between the various components of a complex polymer
mixture. This approach has now been experimentally proven by physicists
from Jülich, who conducted neutron scattering experiments in Grenoble.
The results have been published in the June issue of the journal
Physical Review Letters.
important materials from technology and nature are complex fluids:
polymer melts for plastics production, mixtures of water, oil and
amphiphiles, which can be found in both living cells and in your washing
machine, or colloidal suspensions such as blood or dispersion paints.
They are quite different from simple fluids consisting of small
molecules, such as water, because they are made of mixtures of particles
between a nanometre and a micrometre in size, and have a large number
of so-called degrees of freedom. The latter include vibrations,
movements of the functional groups of molecules or joint movements of
several molecules. They can appear on widely varied length, time, and
energy scales. This makes experimental and theoretical studies difficult
and, so far, has impeded understanding of the properties of these
systems and the targeted development of new materials with improved
method developed and tested by physicists at Forschungszentrum Jülich,
the Institut Laue-Langevin in Grenoble, and the Universities of Vienna
and Rome now permits realistic modelling of complex fluids for the first
microscopic theory describes the interactions between the various
components of a complex mixture and in turn, enables us to draw
realistic conclusions about their macroscopic properties, such as their
structure or their flow properties,” said Prof. Christos Likos of the
University of Vienna, an expert on theory and simulation.
team from Vienna and Rome developed the theory model. Since the
researchers were unable to include all the details of the real system – a
mixture of larger star-shaped polymers and smaller polymer chains –
they systematically eliminated the rapidly moving degrees of freedom and
focused on the relevant slow degrees of freedom, a time-consuming and
do this, we use a relatively new method called coarse graining and
replace each complex macromolecule with a sphere of the appropriate
size. The challenge involves integrating the degrees of freedom that
have been eliminated in the simplified systems as averages so that the
characteristics of the substances are retained,” Likos explained.
team from Jülich used elaborate small angle neutron scattering
experiments with the instrument D11 at the Institut Laue-Langevin in
Grenoble to prove that the interactions between the spheres of the
coarse-grained model realistically simulate the conditions in the real
were faced with the proverbial challenge of visualizing the needle in a
haystack,” explained Dr. Jörg Stellbrink, a physicist and neutron
scattering expert at the Jülich Centre for Neutron Science (JCNS).
neutrons, the individual polymers of the mixture cannot be readily
distinguished. For this reason, the physicists “coloured” the components
they were interested in, so that they stood out of the crowd. This is
one of the Jülich team’s specialities. In this way, they were able to
selectively examine the structures and interactions on a microscopic
physicists are especially proud of the excellent agreement between
theoretical predictions and experimental results. The method will now
open up a spectrum of possibilities for studying the physical properties
of a whole range of different complex mixtures.
Study abstract: Ultrasoft Colloid/Polymer Mixtures: Structure and Phase Diagram;