THESIS
2017
xx, 88 pages : illustrations (some color) ; 30 cm
Abstract
Vapour deposition can directly form ultra-stable glasses which are similar to conventional
glasses aged over thousands years after quenching from the liquid. It is believed
that the highly mobile surface layer accelerates the ageing process of vapour-deposited
glasses, but its microscopic kinetics has not been experimentally observed. Here we
studied the deposition growth kinetics of a two-dimensional colloidal glass at the single-particle
level using video microscopy. We found that newly deposited particles in the
surface layer (depth d 14 particles) relaxed with frequent out-of-cage motions, while
particles in the deeper middle layer (14 d ≲ 100 particles) relaxed via activations of
cooperative-rearrangement regions (CRRs). These CRRs were much larger, anisotropic
and occu...[
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Vapour deposition can directly form ultra-stable glasses which are similar to conventional
glasses aged over thousands years after quenching from the liquid. It is believed
that the highly mobile surface layer accelerates the ageing process of vapour-deposited
glasses, but its microscopic kinetics has not been experimentally observed. Here we
studied the deposition growth kinetics of a two-dimensional colloidal glass at the single-particle
level using video microscopy. We found that newly deposited particles in the
surface layer (depth d < 14 particles) relaxed with frequent out-of-cage motions, while
particles in the deeper middle layer (14 < d ≲ 100 particles) relaxed via activations of
cooperative-rearrangement regions (CRRs). These CRRs were much larger, anisotropic
and occurred more frequently than those in the bulk (d ≳ 100 particles) or after deposition.
The centers of masses of CRRs moved toward the surface, while particles in CRRs
moved toward the bulk, resulting free-volume "bubbles" moving toward the surface and
making the bulk glass more compact. Such two-step relaxation in two surface layers is
distinct to the previously assumed relaxation in one surface mobile layer.
The frictional dynamics of monolayer crystal on a tilted commensurate energy
landscape was studied at single particle level using video microscope. For small tilting
angle θ < 0.08 rad, the crystal remains motionless due to a static frictional force. For an
intermediate tilting angle 0.08 < θ < 0.012 rad, pairs of kinks and antikinks started to
nucleate and propagated along the symmetry direction of the crystal. Further increase
of tilting angle θ > 0.12 rad leads to the formation of clusters of kinks, within which the
atoms sliding freely, which dramatically increased the system mobility. Our research
illustrates a way of studying the Frankel-Kontorova model by using colloids.
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