Rheological Investigations on the Creaming of Depletion-Flocculated Emulsions

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Rheological Investigations on the Creaming of Depletion-Flocculated Emulsions. / Aben, Simon; Holtze, Christian; Tadros, Tharwat; Schurtenberger, Peter.

I: Langmuir, Vol. 28, Nr. 21, 2012, s. 7967-7975.

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Aben, Simon ; Holtze, Christian ; Tadros, Tharwat ; Schurtenberger, Peter. / Rheological Investigations on the Creaming of Depletion-Flocculated Emulsions. I: Langmuir. 2012 ; Vol. 28, Nr. 21. s. 7967-7975.

RIS

TY - JOUR

T1 - Rheological Investigations on the Creaming of Depletion-Flocculated Emulsions

AU - Aben, Simon

AU - Holtze, Christian

AU - Tadros, Tharwat

AU - Schurtenberger, Peter

PY - 2012

Y1 - 2012

N2 - 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.

AB - 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.

U2 - 10.1021/la300221m

DO - 10.1021/la300221m

M3 - Article

VL - 28

SP - 7967

EP - 7975

JO - Langmuir

JF - Langmuir

SN - 0743-7463

IS - 21

ER -