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SUMMARY:A Molecular Mechanism for Toughening and Strengthening Waterborne 
 Nanocomposites - Dr Joe Keddie\, School of Electronics and Physical Scienc
 es\, University of Surrey
DTSTART:20070518T131500Z
DTEND:20070518T141500Z
UID:TALK6925@talks.cam.ac.uk
CONTACT:Dr Kalin Dragnevski
DESCRIPTION:An effective\, yet simple\, method for creating nanocomposite 
 coatings\, fibres\, and adhesives is to blend an aqueous suspension of car
 bon nanotubes (CNTs) with either a polymer solution or waterborne colloida
 l polymer particles (i.e. latex). In processing these waterborne nanocompo
 sites\, there is a wide choice of water-soluble polymers to disperse CNTs 
 in water.  Surfactants are frequently used\, however\, because they are hi
 ghly effective dispersants.  To what extent  - or why - the choice of disp
 ersant might influence nanocomposite mechanical properties has not been co
 nsidered.  In this lecture\, I will show that the dispersant can increase 
 the stress transfer between a nanotube and the matrix\, which is essential
  for achieving high stiffness\, while still allowing interfacial slippage 
 to increase energy dissipation.  I will demonstrate that the mechanism of 
 stress transfer is through interfacial friction from molecular entanglemen
 ts. A high molecular-weight polymer dispersant creates a polymer brush tha
 t entangles with the soft matrix.  Surfactants and low molecular-weight po
 lymers cannot entangle\, therefore yielding far inferior mechanical proper
 ties.  The dispersant’s molecular weight thus provides a means to tune t
 he mechanical and adhesive performance of waterborne nanocomposites.
LOCATION:IRC in Superconductivity Seminar Room\, Cavendish Laboratory
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