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Program Objectives
The focus of the priority programme is the investigation of dense amorphous polymer phases at or near a solid surface. Particular attention is given to the so-called interphase, i.e. the region of the polymer phase where its properties have not quite reached their bulk values. The thickness of the interphase depends not only on the type of polymer and solid and on their interactions, but also on the property under investigation. The mass density, for example, reaches its bulk value much earlier than the cross-link density of a reactive system. Polymer-solid contacts play an important role in technology, from adhesion and coatings to nanocomposites. Yet, the research of the priority programme 1369 is aimed at the fundamental understanding of the interface and interphase, and not at particular material combinations for particular applications. The investigations are to be carried out using modern methods of preparation, characterization and theory.
Research Areas
The 19 research projects fall into two main research areas.
A. Understanding and Controlling the Molecular Structure of the Interphase
Experimental and theoretical methods are used to characterize the molecular structure, orientation, chain-end distribution, cross-link density etc. of the polymer at and near the interface with the solid. The experimental and simulational characterisation methods have a high spatial and, where necessary, temporal resolution. In addition, targeted synthesis or modification of the polymer in this region allows the preparation of interphases with predetermined structure for further characterization.
B. Property Profiles
The local properties of the polymer change through the interphase as a function of the distance to the interface until, at a certain distance, bulk behaviour is reached. This causes local variations not only of the molecular properties but also of properties, which are typically regarded as macroscopic, such as mechanical, dielectrical, optical and transport properties. The thickness of the interphase depends not only on the chemical nature of the system, but also on the property investigated. The density, for example, may reach its bulk value in a few ångströms, whereas the dielectric properties or the permeability need dozens or hundreds of nanometers. This research area aims to resolve polymer properties locally, so that the nature and the extent of the interphase, as apparent in different quantities, can be studied. Methods include characterization and theory as well as targeted preparation.
Research Projects
The projects typically employ combinations of different techniques or even different classes of techniques, such as preparation and characterization, or experiment and theory. This is done within one project or in dedicated and synchronized collaborations between projects. Similarly, many projects serve both research areas, but with different weights. Because of the cooperative and interdisciplinary nature of the projects, they cannot be categorised uniquely by either systems or techniques. The following attempt is meant as a way to provide a rough classification.
The branch systems contains projects, which are dedicated to the preparation and analysis of specific polymer-solid systems or model systems. They include specifically tailored systems with precise control of the molecular architecture near the interface (grafted polymers, polyelectrolyte multilayers), systems which allow easier access to interfacial properties and can serve as models (thin films), systems with an increased volume fraction of interphase (highly-filled nanocomposites, reinforced elastomers), which facilitate the use of non-interface-sensitive techniques (e.g. NMR) for the study of interphases, as well as systems which allow for the added complexity of network formation near an interface (reactive systems). The projects in this branch make use of a variety of techniques, too, and develop or adapt them where needed.
The branch methods collects those projects which are described best by a technique which is applied to a variety of systems. There are characterisation methods like depth-resolved positron annihilation spectroscopy and microscopy on the experimental side, as well as new simulation techniques. |
