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Microscopic investigations of homogeneous nucleationin charged sphere suspensions
We studied the homogeneous nucleation kinetics of an aqueous suspension of charged colloidal spheres under de-ionized conditions. Samples of equilibrium crystalline structure were shear molten and the metastable melt left to solidify after cessation of shear. At low particle number densities n , cor...
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| Published in: | The Journal of chemical physics 2005-10, Vol.123 (17), p.174902-174902-11 |
|---|---|
| Main Authors: | , , |
| Format: | Article |
| Language: | |
| Citations: | Items that this one cites |
| Online Access: | Get full text |
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| Summary: | We studied the homogeneous nucleation kinetics of an aqueous suspension of charged colloidal spheres under de-ionized conditions. Samples of equilibrium crystalline structure were shear molten and the metastable melt left to solidify after cessation of shear. At low particle number densities
n
, corresponding to low metastability of the melt, nucleation was monitored directly via video microscopy. We determined the nucleation rates
Γ
(
t
)
by counting the number of newly appearing crystals in the observation volume per unit time. Using a suitable discrete adaptation of
Avrami
's [
J. Chem. Phys.
7
,
1003
(
1939
)
;
J. Chem. Phys.
8
,
212
(
1940
)
;
J. Chem. Phys.
9
,
177
(
1941
)
] model for solidification via homogeneous nucleation and subsequent growth, we calculate the remaining free volume
V
F
(
t
)
to obtain the rate densities
J
(
t
)
=
Γ
(
t
)
∕
V
F
(
t
)
. We observe
J
(
t
)
to rise steeply, display a plateau at a maximum rate density
J
max
, and to decrease again. With increased
n
the plateau duration shrinks while
J
max
increases. At low to moderate number densities fully solidified samples were analyzed by microscopy to obtain the grain-size distribution and the average crystallite size
⟨
L
⟩
. Under the assumption of stationarity, we obtained the nucleation rate density
J
Avr
, which increased strongly with increasing
n
. Interestingly,
J
Avr
agrees quantitatively to
J
max
and to
J
Avr
as obtained previously from scattering data taken on the same sample at large
n
. Thus, by combination of different methods, reliable nucleation rate densities are now available over roughly one order of magnitude in
n
and eight orders of magnitude in
J
. |
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| ISSN: | 0021-9606 1089-7690 |
| DOI: | 10.1063/1.2075047 |