Variations around disordered close packings: geometrical investigations of non-crystalline matter
by Dr Tomaso Aste
Abstract: A common paradigm in science tends to assume that things are naturally inclined to pursuit order and perfection. When the atomic structure of materials is concerned, such a paradigmatic order is achieved by the endless periodic repetition of local motifs in crystals. Indeed, crystalline order is a convenient and efficient way of packing elements in space. But conversely disorder is everywhere. This is in particular the case when the structures of complex materials are concerned as, for instance, in nanomaterials, in polymers, in biological systems, in glasses
or in granular matter. The actual driving mechanisms that lead to such
disordered structures are very diverse but the resulting structures have
common features and properties that are the consequence of unavoidable
geometrical and topological constraints. In these systems, disorder is not randomness: these structures are highly organized both at local and global scale but nevertheless they don't reveal any periodic (or quasi-periodic) pattern. The study of such structures is very challenging and requires the development of new paradigm and innovative investigation tools.
In the seminar I'll present an extensive study of the geometrical structure of non-crystalline matter based on an experimental investigation, with x-ray computed tomography, of large packings of monosized spheres. I discuss topological and geometrical methods to characterize and classify these systems emphasizing the implications that local geometry can have on the properties and on the mechanisms of formation of these amorphous structures. I search for signatures of organization, classifying local arrangements and exploring the effects of local geometrical constrains on the global packing. This study is the largest and the most accurate analysis of disordered packings at the
grain-scale to date, mapping over 380 000 sphere coordinates with precision within 0.1% of the sphere diameters.
For More Information: Paul Norbury tel. 8344 5534 http://www.ms.unimelb.edu.au/~pnorbury/colloquium/colloquium-2005.html