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SUMMARY:Understanding the Dynamics of Unentangled Associating Polymers by 
 Means of Molecular Simulations - Professor Jorge Ramírez García\, Univer
 sidad Politecnica De Madrid
DTSTART:20190605T131500Z
DTEND:20190605T141500Z
UID:TALK121978@talks.cam.ac.uk
CONTACT:Lisa Masters
DESCRIPTION:Associating polymers are a family of macromolecules that have 
 sticky groups that can create intermolecular reversible bonds with energie
 s on the order of a few tens of kT. These bonds can associate and dissocia
 te easily at room temperature and\, above the percolation threshold\, asso
 ciating polymers form transient solid soft materials. These materials have
  many applications as sacrificial components in tough physical double netw
 orks\, synthetic matrices for tissue engineering\, injectable biomaterials
  for minimally invasive surgery or self-healing soft materials. In all cas
 es\, it is very important to understand and predict both the dynamical res
 ponse of the material (i.e. its mechanical properties or the diffusion of 
 the network forming constituents).\nRecent experiments have revealed that 
 a variety of unentangled associative polymers with different architectures
  and different nature of the associating interactions exhibit an unexpecte
 d diffusion behavior\, with a phenomenological superdiffusive scaling at l
 ength-scales and time-scales much longer than the molecular size and relax
 ation time. In this talk\, I will discuss a new coarse-grained molecular m
 odel of unentangled associating polymers that successfully explains the ob
 served anomalous behavior and reveals three basic mechanisms of molecular 
 diffusion: caging dynamics\, walking diffusion and molecular hopping\, all
  of which depend very strongly on polymer concentration\, length of the se
 gments between stickers and the association/dissociation kinetics. The app
 arent superdiffusive scaling results primarily from molecular hopping\, wh
 ich dominates the dynamics at long times if the kinetics of attachment are
  much slower than the relaxation time of polymer strands between stickers 
 and the formation of loops is favourable. Finally\, I will discuss how the
  molecular parameters affect the diffusivity and relaxation modulus\, as w
 ell as the non-linear flow behaviour\, and how to confirm other prediction
 s of the model experimentally and by means of Molecular Dynamics simulatio
 ns.
LOCATION:Department of Chemistry\, Cambridge\, Unilever lecture theatre
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