Project number		Stand-alone Projects  P18592
Title		Phase transitions and correlations in complex fluids
Principal investigator		FOLK Reinhard
Approval date		10.10.2005
University / Research institution		Institut für Theoretische Physik, Universität Linz
Scientific field(s)
Keywords		Condensed Matter Physics, Computer Stimulations, Integral Equation Methods, Critical Phenomena, Renormalization Group Theory, Dynamical Properties
Homepage		http://www.tphys.jku.at/group/folk/folk.html

The description of physical systems as liquids or magnets starts from simple models like a system of movable spheres interacting with a distance dependent potential or elementary magnets (spins) sitting on a lattice with an interaction only dependent on the direction of these spins. Even in such simple models a rich phase behavior can be observed and the description of this is difficult. Before one applies such models to real systems one has to clarify what the model itself can accomplish and which properties can be analytically described. The first point can be checked by simulations (Mont Carlo simulations or molecular dynamic simulations), the last point is studied by using analytic approximation methods like integral equation methods for liquid systems. But even then one gets a system of equations which can be solved only numerically but from the results one can get ideas what is important for a certain phase or at a certain phase transition.

At special points, lines or surfaces in the thermodynamic phase space, depending on the topology of the phase diagram, one finds special phase transitions where physical quantities behave singular. For example the thermal conductivity of a liquid diverges at the critical point. The description of such a behavior needs special renormalization group theoretical methods, since the system loses its typical length- and time scales at this special point.

In this project starting from earlier development made by the project group and results of others complex systems like magnetic liquids and mixtures, ionic solutions (charged liquid particles), mixtures of He³ and He⁴, which show a superfluid phase and a tricritical line, but also solid state systems like ferro- and antiferromagnets will be studied. We consider static and dynamical properties of these systems.

The goal of the project is on the one hand to explain quantitative experimental results (e.g. the temperature and concentration dependence of transport coefficients in He³-He⁴ mixtures near the tricritical point, or the dynamical structure function in ferro- and antiferromagnets near the Curie and Neel point, respectively, or the excitations in magnetic ionic or dielectric liquids) on the other hand the methods used should be developed (e.g. the method of integral equations in order to achieve better thermodynamic consistency).