Drop formation of Carbopol dispersions displaying yield stress, shear thinning and elastic properties in a flow-focusing microfluidic channel

Hong, Joung Sook and Cooper-White, Justin (2009) Drop formation of Carbopol dispersions displaying yield stress, shear thinning and elastic properties in a flow-focusing microfluidic channel. Korea-Australia Rheology Journal, 21 4: 269-280.

Author Hong, Joung Sook
Cooper-White, Justin
Title Drop formation of Carbopol dispersions displaying yield stress, shear thinning and elastic properties in a flow-focusing microfluidic channel
Journal name Korea-Australia Rheology Journal   Check publisher's open access policy
ISSN 1226-119X
Publication date 2009-12
Year available 2009
Sub-type Article (original research)
Open Access Status
Volume 21
Issue 4
Start page 269
End page 280
Total pages 12
Editor Hyungsu Kim
Ravi P. Jagadeeshan
Place of publication Korea
Publisher The Korean Society of Rheology
Collection year 2010
Language eng
Subject 1007 Nanotechnology
C1
Abstract The drop formation dynamics of a shear thinning, elastic, yield stress (τ o) fluid (Carbopol 980 (poly(acrylic acid)) dispersions) in silicone oil has been investigated in a flow-focusing microfluidic channel. The rheological character of each solution investigated varied from Netwonian-like through to highly non-Newtonian and was varied by changing the degree of neutralization along the poly (acrylic acid) backbone. We have observed that the drop size of these non-Newtonian fluids (regardless of the degree of neutralisation) showed bimodal behaviour. At first we observed increases in drop size with increasing viscosity ratio (viscosity ratio=viscosity of dispersed phase (DP) / viscosity of continuous phase (CP)) at low flowrates of the continuous phases, and thereafter, decreasing drop sizes as the flow rate of the CP increases past a critical value. Only at the onset of pinching and during the high extensional deformation during pinch-off of a drop are any differences in the non-Newtonian characteristics of these fluids, that is extents of shear thinning, elasticity and yield stress (τ o), apparent. Changes in these break-off dynamics resulted in the observed differences in the number and size distribution of secondary drops during pinch-off for both fluid classes, Newtonian-like and non-Newtonian fluids. In the case of the Newtonian-like drops, a secondary drop was generated by the onset of necking and breakup at both ends of the filament, akin to end-pinching behavior. This pinch-off behavior was observed to be unaffected by changes in viscosity ratio, over the range explored. Meanwhile, in the case of the non-Newtonian solutions, discrete differences in behaviour were observed, believed to be attributable to each of the non-Newtonian properties of shear thinning, elasticity and yield stress. The presence of a yield stress (τ o), when coupled with slow flow rates or low viscosities of the CP, reduced the drop size compared to the Newtonian-like Carbopol dispersions of much lower viscosity. The presence of shear thinning resulted in a rapid necking event post onset, a decrease in primary droplet size and, in some cases, an increase in the rate of drop production. The presence of elasticity during the extensional flow imposed by the necking event allowed for the extended maintenance of the filament, as observed previously for dilute solutions of linear polymers during drop break-up.
Keyword yield stress
shear thinning behavior
drop deformation
flow focusing
microfluidics
Q-Index Code C1
Q-Index Status Confirmed Code
Institutional Status Unknown

Document type: Journal Article
Sub-type: Article (original research)
Collections: 2010 Higher Education Research Data Collection
Australian Institute for Bioengineering and Nanotechnology Publications
 
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Created: Sun, 24 Jan 2010, 00:01:36 EST