Shear modulus as a function of temperature for glassy polystyrene. The solid line is the prediction of the theory of Zaccone & Terentjev, whereas circles are experimental data from the literature.
The "Special Relationship" goes scientific. A new partnership has officially started last week between CEB and the US Army Research Laboratory, initiated by Dr Alessio Zaccone, head of the Statistical Physics Group at CEB. Within this partnership, the US Army Research Lab provides funding for a Research Associate position within Dr Zaccone’s group. This position has been assigned to Dr Vladimir Palyulin (previously Research Associate in the Physics Department of Technical University Munich), who took service at CEB on 1 October.
The main goal of this partnership is to develop new chemical-design principles for amorphous polymers with outstanding mechanical properties to be used as smart materials for protective equipment of land forces. Polymers (or plastics) are ubiquitous in technological applications, and they typically present a molecular-level disordered structure whereby long macromolecular chains appear intermingled in a chaotic fashion. The most important feature of polymer materials is their glass transition temperature. Above this temperature, polymers form a melt of mobile chains with marginal rigidity provided by entanglements.
The molecular-level explanation of the properties of polymer melts led to the 1991 Nobel prize in Physics being awarded to Pierre-Gilles de Gennes, although substantial contributions to the theory came from Sir Sam Edwards of the Cavendish Laboratory at Cambridge. Below the glass transition temperature, polymers appear as solid and rigid materials, with a disordered molecular-level structure where the macromolecular chains are frozen-in spatially and dynamically. In this regime, where the dynamics cannot be explained by de Gennes and Edwards’ theories, the only theoretical analytical framework that successfully describes the thermo-elastic response of polymers in their glassy state, and in particular the drop by many orders of magnitude of their elastic modulus upon approaching the glass transition from lower temperatures, was presented by Dr Zaccone and Prof Terentjev in a 2013 article appeared in Physical Review Letters (http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.110.178002).
This theoretical framework, which is based on the key concept of nonaffine molecular displacements, will now be extended and combined with state-of-the-art atomistic simulations developed by Dr Timothy Sirk and his research group at the US Army Lab. In this way, guiding principles will be sought towards the discovery of new polymers that optimize the energy absorption, ductility and resistance to shocks and blasts for protective equipment to be used in land war context.