Soft Report - Dipartimento di Fisica - Sapienza

Missioncolloids and soft colloidal systems, selecting the model systems among the mostprominent candidates for grasping the essential features of dynamic arrest.Emphasis is on the possibility of performing a detailed comparison betweenexperimental data and theoretical predictions based also on the mode couplingtheory of the glass transition. We focus on understanding the system's kineticarrest phase diagram, i.e. the regions in phase space where disordered arrestedstates can be expected, both gels and glasses. We examine when and how thesestates are kinetically stabilized with respect to the ordered lowest free energyphases, in order to provide a framework for interpreting and developing new ideasin the study of new materials. Finally, we study chemical gels to investigate theunderlaying universal properties of gelation and glass formation.C. Elastic and inelastic X-ray and neutron scatteringSoft matter, including glasses, polymers and biological matter, though beingmacroscopically isotropic, has different properties due to its microscopic structureand dynamics. Specific and universal trends are observed at the same time and arelationship with the microscopic and mesoscopic behaviour is expected. Most ofthe activity is performed at the beam lines in Grenoble where both the scientificactivity and the technical advances in neutron and x-ray scattering represent arelevant enterprise. A close cooperation of the group in Grenoble and variousgroups in Italy is a relevant added value which makes this activity interdisciplinary.Activities are organized around complementary research projects.C1. Technical developmentsFour beam lines represent the major technical effort. These beam lines are installedat the neutron and photon sources ILL and ESRF located in Grenoble (France) andare almost unique facilities in the world.The two neutron beam lines are IN13 and BRISP. The first one is a backscatteringthermal neutron spectrometer useful for quasi-elastic investigations in the µeVrange up to 5 Å -1 momentum transfer. This performance make this instrumentextremely important in the study of relatively slow (5-100 ps) relaxation processesin disordered systems like glasses and biological molecules. The instrument hasbeen almost rebuilt in the last years thus improving its performances in terms ofmomentum-energy range and in terms of intensity (see detailed description). Thesecond instrument, BRISP, has been completed in 2005 essentially on timeschedule and during the two reactor cycles of 2006 has been commissioned. Thisinstrument is devoted to the study of dynamics of disordered systems with specialconcern for the collective dynamics with sound velocity ranging from 500 m/sto4000 m/s (see detailed description). This is a unique machine and its constructionimplied a big effort in terms of technical developments because it employs newsolutions, never developed before.The two photon instruments are ID16 and AXES. The first one initiated the study ofcollective dynamics employing ultra-high resolution x-ray scattering, thusintroducing the companion technique of neutron scattering. ID16 is the x-raycounterpart of BRISP and the two instruments perform complementary and parallelSOFT Scientific Report 2004-0612