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Abstract: As the largest class of inorganic macromolecules, polyphosphazenes have unique backbones that contain alternating nitrogen and phosphorus atoms. Starting from the chlorinated parent polymer, polyphosphazenes have tunable properties and hence are widely applied in different fields. However, in contrast to the intense functionalization and application studies, few works have reported the polymerization mechanism to explain the intricacies of the reaction process. Despite the advancements in sophisticated analytical chemistry techniques and cutting-edge technologies, seizing and analyzing the high-energy reaction intermediates remains a formidable challenge although numerous attempts have been made. As a result, the lack of understanding of the reaction mechanism has significantly plagued the refinements and developments of polymer synthesis and hence hindered the bulk use of novel materials. This presentation will give a quick walk through of the recent efforts in exploration of the monomer formation, ring-opening (ROP) and ring-ring expansion (RR) of [PCl₂N]₃ using quantum mechanical calculations. These findings can provide invaluable guidance for further experimental mechanistic studies through instrumental analysis, and also shed light on some mysteries that have remained elusive in over 200 years of chlorophosphazene research. Specifically, what are potential "tadpole" compounds, what can trigger crosslinking reactions and why there is a coexistence of linear and cyclic products in polymer synthesis.

Speaker: Brookhaven National Laboratory 

 

Title: Heavy ion physics, or how an ugly duckling turned into a beautiful swan

 

Abstract: I give a pedagogical and historical overview for the search of a new state of matter - the Quark-Gluon Plasma (QGP) - in the collisions of heavy ions at very high energies. We now know that neutrons and protons are produced by Quantum ChromoDynamics, or QCD.  At high temperature, we expect a transition to a region where neutrons and protons are replaced by quarks and gluons.  In this, numerical simulations in lattice Quantum ChromoDynamics (QCD) form the bedrock of the field and give us a firm understanding of the phase transitions which are expected. Bjorken first noticed that a "plateau" may emerge at high energies, and produce a regime at high temperature, and low chemical potential, in the collisions of heavy ions in the "middle" of the collision. At colliders such as RHIC, at Brookhaven, and the LHC, at CERN, I discuss two notable signals: the utility of nearly ideal hydrodynamics, and jet quenching. The new frontier is going down to moderate collision energies, which include a critical end point and moat regimes.

 

Host: CNR