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SUMMARY:Implications from the ratio of surface tension to bulk modulus and
  nearest neighbour distance\, for planar surfaces - A E Phillips (Cavendis
 h Laboratory\, University of Cambridge)
DTSTART:20081205T160000Z
DTEND:20081205T163000Z
UID:TALK15048@talks.cam.ac.uk
CONTACT:Daniel Cole
DESCRIPTION:*from "the paper by Graham Weir":http://dx.doi.org/10.1098/rsp
 a.2007.0360*\n\nThe theory of impact between nano-sized particles leads to
  the important non-dimensional grouping γ/_aB_\, where γ\, _a_ and _B_ a
 re the effective surface energy\, effective near neighbour distance\, and 
 effective bulk modulus for the impacting surfaces. A general\, though form
 al\, expression for γ/_aB_ is obtained for a planar surface\, and a modif
 ied Lennard-Jones analysis suggests that this grouping is of the order of 
 several per cent. Bounds are suggested on this ratio\, which are verified 
 for many of the elements about their melting points\, for several liquids 
 at 298 K\, and for the liquified noble gases. It is suggested that\, at th
 e atomic scale\, the ratio between yield stress and the bulk modulus is al
 so approximately equal to this grouping\, which would make impacts between
  nano-scaled surfaces very much harder than for macroscopic impacts. Howev
 er\, γ/_aB_ is material dependent and can vary by a factor of two or more
  about its median value. Subject to such variation\, it is suggested that\
 , to leading order\, collisions between pure nanoscale particles depend pr
 imarily on the number of atoms in the clusters\, and on a non-dimensional 
 velocity scale\, for low-velocity impacts. The expression for γ/_aB_ is e
 valuated approximately in planar geometry by assuming that interactions be
 tween surface atoms (or molecules) only involve radial pair surface intera
 ctions.
LOCATION:TCM Seminar Room\, Cavendish Laboratory
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