Glassy dynamics at hard and soft interfaces_

Talk by Dr. Thomas Blochowicz

Institut für Festkörperphysik TU-Darmstadt

Glassy dynamics at hard and soft interfaces: cooperativity and confinement on the nanoscale

When a liquid is supercooled, molecular dynamics slows down by many orders of magnitude within a comparatively small temperature interval until the glass transition temperature is reached. At that point transport coefficients, like the dynamic viscosity, reach values typical of solid materials. This dynamic slowing down is often understood in terms of a growing length scale of cooperative motion. In search for experimental evidence for such a cooperative length scale supercooled liquids are studied in various confinement situations. One expects that, if the molecules are subject to a small enough geometrical restriction, the competition between the lengthscales of cooperativity and confinement will produce a clear signature in the dynamics. However, the interplay between density, interface and finite-size effects in confined supercooled liquids leads to a complex dynamical behaviour, that so far is not well understood.

In the talk I will present a combination of relaxation and scattering techniques (dielectric spectroscopy, calorimetry, neutron, X-ray and light scattering) that allow to access molecular dynamics of supercooled liquids in various confinement situations and on different time and length scales. The confinements that are discussed range from hard confinement in nanoporous silica matrices to soft confinement within microemulsion droplets. Moreover, more complex cases of so-called intrinsic confinement situations are considered, which are also interesting from an application point of view. Such a confinement occurs within dynamically asymmetric blends, that can be regarded as model materials, e.g., for polymer plasticizer systems. Here, recent investigations have shown that inner surfaces and intrinsic confinement effects play an important role for the dynamics and are responsible for an unusual type of glass transition that was previously predicted by theory but only recently identified in experiments.

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