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Rotational averaging-out gravitational sedimentation of colloidal dispersions and phenomena | | Djamel El Masri
; Teun Vissers
; Stephane Badaire
; Johan C.P. Stiefelhagen
; Hanumantha Rao Vutukuri
; Peter Helfferich
; Tian Hui Zhang
; Willem K. Kegel
; Arnout Imhof
; Alfons van Blaaderen
; | | Date: |
18 Nov 2011 | | Abstract: | We report on the differences between colloidal systems left to evolve in the
earth’s gravitational field and the same systems for which a slow continuous
rotation averaged out the effects of particle sedimentation on a distance scale
small compared to the particle size. Several systems of micron-sized colloidal
particles were studied: a hard sphere fluid, colloids interacting via
long-range electrostatic repulsions above the freezing volume fraction, an
oppositely charged colloidal system close to either gelation and/or
crystallization, colloids with a competing short-range depletion attraction and
a long-range electrostatic repulsion, colloidal dipolar chains, and colloidal
gold platelets under conditions where they formed stacks. Important differences
in the structure formation were observed between the experiments where the
particles were allowed to sediment and those where sedimentation was averaged
out. For instance, in the case of colloids interacting via long-range
electrostatic repulsions, an unusual sequence of
dilute-Fluid/dilute-Crystal/dense-Fluid/dense-Crystal phases was observed
throughout the suspension under the effect of gravity, related to the volume
fraction dependence of the colloidal interactions, whereas the system stayed
homogeneously crystallized with rotation. For the oppositely charged colloids,
a gel-like structure was found to collapse under the influence of gravity with
a few crystalline layers grown on top of the sediment, whereas when the
colloidal sedimentation was averaged out, the gel completely transformed into
crystallites that were oriented randomly throughout the sample. Rotational
averaging out gravitational sedimentation is an effective and cheap way to
estimate the importance of gravity for colloidal self-assembly processes. | | Source: | arXiv, 1111.4436 | | Services: | Forum | Review | PDF | Favorites | |
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