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Rheological Investigations on the Creaming of Depletion-Flocculated Emulsions

Aben, Simon; Holtze, Christian; Tadros, Tharwat and Schurtenberger, Peter LU (2012) In Langmuir 28(21). p.7967-7975
Abstract
Preventing creaming or sedimentation by the addition of thickeners is an important industrial challenge. We study the effect of the addition of a "free" nonadsorbing polymer (xanthan gum) on the stability against creaming of sterically stabilized O/W emulsions. Therefore, we analyze our samples using microscopy and rheological measurements. At low xanthan concentrations, the emulsions cream. However, above a certain concentration a three-dimensional network of droplets is formed, which can prevent creaming. We attribute the formation of this structure to depletion attraction. The rheological behavior of an emulsion that is macroscopically stable should be elastic, while it should be viscous for a creaming emulsion. In order to distinguish... (More)
Preventing creaming or sedimentation by the addition of thickeners is an important industrial challenge. We study the effect of the addition of a "free" nonadsorbing polymer (xanthan gum) on the stability against creaming of sterically stabilized O/W emulsions. Therefore, we analyze our samples using microscopy and rheological measurements. At low xanthan concentrations, the emulsions cream. However, above a certain concentration a three-dimensional network of droplets is formed, which can prevent creaming. We attribute the formation of this structure to depletion attraction. The rheological behavior of an emulsion that is macroscopically stable should be elastic, while it should be viscous for a creaming emulsion. In order to distinguish between stable and unstable samples, we measure their relaxation time by mechanical rheology and find a good correlation to the visual observation. However, the measured relaxation times are much shorter than the time-scales, on which we observe creaming. We hypothesize that the measured relaxation time is related to the droplet-droplet interaction. This determines the frequency at which microscopic rearrangements occur, which weaken the network structure prior to creaming. Based on this interpretation, the relaxation time gives direct access to the microstructural processes involved in creaming. We therefore suggest using it as a predictive parameter of creaming stability. (Less)
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author
organization
publishing date
type
Contribution to journal
publication status
published
subject
in
Langmuir
volume
28
issue
21
pages
7967 - 7975
publisher
The American Chemical Society
external identifiers
  • wos:000304492700005
  • scopus:84861645539
ISSN
0743-7463
DOI
10.1021/la300221m
language
English
LU publication?
yes
id
ae131e6e-f898-46ec-b9b8-5c4813b01ea2 (old id 2906903)
date added to LUP
2012-07-23 15:37:18
date last changed
2017-10-08 03:15:30
@article{ae131e6e-f898-46ec-b9b8-5c4813b01ea2,
  abstract     = {Preventing creaming or sedimentation by the addition of thickeners is an important industrial challenge. We study the effect of the addition of a "free" nonadsorbing polymer (xanthan gum) on the stability against creaming of sterically stabilized O/W emulsions. Therefore, we analyze our samples using microscopy and rheological measurements. At low xanthan concentrations, the emulsions cream. However, above a certain concentration a three-dimensional network of droplets is formed, which can prevent creaming. We attribute the formation of this structure to depletion attraction. The rheological behavior of an emulsion that is macroscopically stable should be elastic, while it should be viscous for a creaming emulsion. In order to distinguish between stable and unstable samples, we measure their relaxation time by mechanical rheology and find a good correlation to the visual observation. However, the measured relaxation times are much shorter than the time-scales, on which we observe creaming. We hypothesize that the measured relaxation time is related to the droplet-droplet interaction. This determines the frequency at which microscopic rearrangements occur, which weaken the network structure prior to creaming. Based on this interpretation, the relaxation time gives direct access to the microstructural processes involved in creaming. We therefore suggest using it as a predictive parameter of creaming stability.},
  author       = {Aben, Simon and Holtze, Christian and Tadros, Tharwat and Schurtenberger, Peter},
  issn         = {0743-7463},
  language     = {eng},
  number       = {21},
  pages        = {7967--7975},
  publisher    = {The American Chemical Society},
  series       = {Langmuir},
  title        = {Rheological Investigations on the Creaming of Depletion-Flocculated Emulsions},
  url          = {http://dx.doi.org/10.1021/la300221m},
  volume       = {28},
  year         = {2012},
}