Hypothesis: Shear-banding of branched wormlike solutions is a topic of active investigation which has not been fully elucidated. Here, we surmise that flow-induced microstructuring in the shear banding regime is associated with spatial concentration gradients. Experiments: The experiments focus on the flow-induced behavior of a CTAB/NaSal wormlike micellar system. A unique approach based on a microfluidic-spitter geometry, combined with particle-image velocimetry and high-speed video microscopy, is used to separate the streams flowing out from the core and the near wall zones of the microchannel. Findings: Here, we present the first direct experimental evidence of the correlation between phase separation and shear banding. By increasing the pressure-drop across a microcapillary, the onset of a grainy texture close to the wall, showing a flow-induced demixing effect, is observed. We use a splitter to measure effluent streams from the center and the near-wall zones in terms of viscosity, conductance and dry mass. We observe that phase-separation induced by the flow correlates with chemical concentration gradients. This confirms our hypothesis that shear-induced local de-mixing of the system is strongly related to chemical concentration gradients.

Flow-induced concentration gradients in shear-banding of branched wormlike micellar solutions / Caiazza, C.; Preziosi, V.; Tomaiuolo, G.; O'Sullivan, Patrick; Guida, V.; Guido, S.. - In: JOURNAL OF COLLOID AND INTERFACE SCIENCE. - ISSN 0021-9797. - 534:(2019), pp. 695-703. [10.1016/j.jcis.2018.09.060]

Flow-induced concentration gradients in shear-banding of branched wormlike micellar solutions

Preziosi, V.
;
Tomaiuolo, G.;O'SULLIVAN, PATRICK;Guido, S.;
2019

Abstract

Hypothesis: Shear-banding of branched wormlike solutions is a topic of active investigation which has not been fully elucidated. Here, we surmise that flow-induced microstructuring in the shear banding regime is associated with spatial concentration gradients. Experiments: The experiments focus on the flow-induced behavior of a CTAB/NaSal wormlike micellar system. A unique approach based on a microfluidic-spitter geometry, combined with particle-image velocimetry and high-speed video microscopy, is used to separate the streams flowing out from the core and the near wall zones of the microchannel. Findings: Here, we present the first direct experimental evidence of the correlation between phase separation and shear banding. By increasing the pressure-drop across a microcapillary, the onset of a grainy texture close to the wall, showing a flow-induced demixing effect, is observed. We use a splitter to measure effluent streams from the center and the near-wall zones in terms of viscosity, conductance and dry mass. We observe that phase-separation induced by the flow correlates with chemical concentration gradients. This confirms our hypothesis that shear-induced local de-mixing of the system is strongly related to chemical concentration gradients.
2019
Flow-induced concentration gradients in shear-banding of branched wormlike micellar solutions / Caiazza, C.; Preziosi, V.; Tomaiuolo, G.; O'Sullivan, Patrick; Guida, V.; Guido, S.. - In: JOURNAL OF COLLOID AND INTERFACE SCIENCE. - ISSN 0021-9797. - 534:(2019), pp. 695-703. [10.1016/j.jcis.2018.09.060]
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11588/746601
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