Submitted to: Carbohydrate Polymers
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 11, 2005
Publication Date: May 9, 2006
Citation: Kim, S., Xu, J., Biswas, A., Willett, J.L. 2006. Shear-induced aggregate formation in starch solutions. Carbohydrate Polymers. 64(2):168-174. Interpretive Summary: Viscosity measurement is one of the techniques that characterizes starch solutions. Previous work has shown that starch solutions show an unusual behavior during the viscosity measurement. Normally, polymer solutions show a decrease in viscosity with increasing shear rate. However, some starch solutions showed an increase in viscosity with an increasing shear rate. Furthermore, when the sheared solution was observed with an optical microscope, patterns were observed in the solution. In the previous report, it was shown that the anomaly in viscosity and pattern formation are two different phenomena and the reason for the increase in viscosity with increasing shear rate was explained. In this study, the pattern-forming behavior was investigated and the reason for the aggregate formation in starch solutions is explained. As a result of this research, we can better understand the behavior of starch solutions.
Technical Abstract: Shear-thickening behavior and shear-induced pattern formation have been observed in semidilute waxy maize starch solutions. While the shear-thickening behavior is due to breaking up of highly concentrated gel-like structures dispersed in dilute starch solutions, the pattern-forming behavior is not well understood. The pattern formation, observed when the starch solution is exposed to a high shear field, is a consequence of shear-induced aggregation and is not related to shear-thickening behavior. The patterns have been observed above a certain critical threshold shear rate regardless of the starch type. In this report, it is shown that the product of shear time and fourth power of shear rate is a controlling factor for the formation of shear-induced aggregates. Examination of starch particle sizes in various conditions indicates that aggregates are formed from incompletely solubilized starch residue in the system.