IRG 1 - Premelting at defects within bulk colloidal crystals Arjun G. Yodh DMR-0520020

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IRG 1 - Premelting at defects within bulk
colloidal crystals Arjun G. Yodh DMR-0520020
Real time video microscopy has been used to gain
insight into one naturess most basic phenomena
melting of a crystalline solid. Premelting,
the localized loss of crystalline order at
surfaces and defects for temperatures below the
bulk melting transition, can be thought of as
the nucleation of the melting process. We have
found premelting at grain boundaries and
dislocations within bulk colloidal crystals made
from thermally responsive microgel spheres. The
thermal response of the microgel enables
precision control of particle volume fraction.
Particle tracking revealed increased disorder in
crystalline regions bordering defects, the amount
of which depends of the type of defect (e.g.
grain boundaries, dislocations, vacancies),
distance from the defect, and particle volume
fraction. Our observations suggest interfacial
free energy is the crucial parameter for
premelting, in colloidal and atomic scale
crystals. Science, 309 1207-1210 (2005)
We have discovered that crystalline colloids
premelt near defects in crystal, before the bulk
crystal melts. This figure represents a
two-dimensional slice of a three-dimensional
colloidal crystal. A grain boundary, separating
two crystallites with different orientations,
rises from left to right. Near the boundary it
is apparent that colloidal particles (i.e. big
atoms) move rapidly and exhibit liquidlike
diffusion. Red represents the most movement and
violet the least movement.