Research of the Likos Group


Soft Matter Theory & Simulation

Work in our group focuses on the research area of Theoretical and Computational Physics of Soft Condensed Matter. The term Soft Matter encompasses a large variety of systems of fundamental interest, possessing at the same time enormous technological and biological relevance, e.g.: polymers, colloids, DNA-molecules, proteins, membranes etc. Soft systems are characterized through three basic properties: first, they are solutions/suspensions of mesoscopic macromolecular aggregates on a microscopic solvent. Second, in stark contrast to their atomic counterparts, the effective forces between the dissolved particles can be tuned through changes in the architecture of the molecules, the temperature, as well as the salinity and the pH of the solvent. This property renders soft matter systems as prime candidates for the targeted and controlled design of material properties at the molecular scale, since the interparticle interactions dictate the macroscopic equilibrium and dynamical behavior of the system. Finally, another extremely important property of soft matter is its high sensitivity to external fields, which offer an additional possibility to externally steer the behavior of soft materials.

The central approach permeating our research philosophy is to perform accurate coarse-graining processes on the complex, multicomponent systems encountered in soft and biological matter, so as to drastically reduce the inherent complexity and bridge the scales from a (highly complex) microscopic one to a more manageable mesoscopic. Afterwards, the subsequent bridging from the mesoscopic to the macroscopic scale follows through rules, techniques and procedures known from the theory of simple fluids and crystals. This approach has proven extremely fruitful, e.g., in the domain of materials science and engineering, since it allows for the prediction of the forms of self-organization of matter, starting from the basis of the properties and architecture of the constituent macromolecules at the microscopic scale. What is even more important, the technique allows the study of not only equilibrium properties (fluid structure, crystallization) but also of dynamical ones (glass formation and rheology). The typical techniques that we apply along these lines draw from a diverse and mutually complementary pool of approaches, some of which have been co-developed and refined in the group: scaling theory of polymers, density functional theory (static and dynamical), integral equation theories, renormalization-group methods, phonon theories, genetic algorithms, as well as mode coupling theory of glass formation.

The program of the development of effective interactions has been successfully carried out thus far for a variety of systems, for which the length scales from microscopic to macroscopic have been bridged: star polymers, dendrimers, microgels and polyelectrolytes, as well as columnar DNA assemblies with explicit consideration of the helical charge pattern they carry. A host of novel phenomena, including exotic crystal phases, re-entrant melting and vitrification, cluster formation on novel types of cluster crystals and orientational order in columnar DNA assemblies have been discovered and, to a large part, experimentally confirmed. Currently, emphasis is put on non-equilibrium phenomena and on systems of higher complexity, such as glasses, colloid-polymer complexes and polyelectrolytes with explicit solvent. In what follows, a short list of the current research activities in the group is presented.

  • Vitrification in soft mixtures. Collaboration with: Francesco Sciortino and Emanuela Zaccarelli (University of Rome), Dimitris Vlassopoulos (FORTH and University of Crete, Heraklion), Dieter Richter and Jörg Stellbrink (Jülich).
  • Complexation of soft polymers with hard surfaces and colloids. Collaboration with: Matthias Ballauff (Helmholtz-Zentrum Berlin).
  • Telechelic block-copolymer micelles. Collaboration with: Athanassios Z. Panagiotopoulos (Princeton University), Federica Lo Verso (University of Mainz), Dimitris Vlassopoulos (FORTH and University of Crete, Heraklion).
  • Statics and dynamics of cluster formation. Collaboration with: Gerhard Kahl (Vienna University of Technology), Christoph Dellago (University of Vienna), Daan Frenkel (University of Cambridge), Bianca Mladek (Max F. Perutz Laboratories, Vienna).
  • Ordering, arrest, pattern formation and dynamics of two-dimensional magnetic colloids. Collaboration with: Peter Keim and Georg Maret (University of Konstanz), Gerhard Kahl (Vienna University of Technology), Jure Dobnikar (University of Cambridge and Jozef Stefan Institute, Ljubljana), Dušan Babić (University of Ljubljana) and Primoz Ziherl (Jozef-Stefan-Institute, Ljubljana).
  • Theory of interactions of polyelectrolyte brushes. Collaboration with: Jan Dhont (Jülich).
  • Topological constraints for ring polymers. Collaboration with: Angel Moreno (University of the Basque Country, San Sebastián, Spain).
  • Soft matter under shear. Collaboration with: Dimitris Vlassopoulos (FORTH and University of Crete, Heraklion).
  • Charged dendrimers. Collaboration with: Matthias Ballauff (Helmholtz-Zentrum Berlin), Martin Buzza (University of Hull).
  • Genetic algorithms in soft condensed matter. Collaboration with: Gerhard Kahl (Vienna University of Technology).
  • Correlations and dynamics of microgels. Collaboration with: Peter Schurtenberger (Lund University) and Matthias Ballauff (Helmholtz Center Berlin).
  • Novel depletion interactions in star-chain polymer mixtures. Collaboration with: Luciano Reatto and Davide Pini (University of Milan), Alberto Parola (University of Como), and Federica Lo Verso (University of Mainz).