Seminar"Manipulating yield-stress fluids with ultrasound-activated microbubbles" Prof. Valeria Garbin


Wednesday, November 11, 2020 - 16:00




Micro/Bio/Nanofluidics (Shen) Unit would like to invite you to the virtual seminar by Prof. Valeria Garbin on September 28 (Monday).

Date: Wednesday, November 11, 2020
Time: 16:00-17:00
**Zoom session

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Meeting ID: 932 5909 3240
Passcode: 912969


Prof. Valeria Garbin
Department of Chemical Engineering
Delft University of Technology


Manipulating yield-stress fluids with ultrasound-activated microbubbles


Yield-stress fluids are widely used in the personal care, food engineering and construction materials industries because of their unique property of behaving as elastic solids under a given applied stress named yield stress. They may trap small bubbles, with either beneficial (e.g. for ice cream) or detrimental (e.g. in ceramics or concrete) effects, driving the need to control their bubble content. Ultrasound excitation of bubbles has already been shown to be a promising tool to remove bubbles from shear-thinning fluids. Acoustic waves induce rapid bubble dilation and compression cycles leading to a periodic, purely extensional strain field in the material, which may suffice to induce yielding and bubble release. We recently developed a theoretical model describing bubble dynamics in yield-stress fluids, to estimate the critical acoustic pressure required to initiate yielding and to provide guidelines to pinpoint the yielding transition in experiments. We then conducted experiments in a Carbopol microgel where small bubbles are excited using ultrasound at 10-100 kHz and imaged with a high-speed camera. We investigate the net motion of the bubble across the predicted yield point and analyse the influence of bubble shape oscillation on bubble mobility in the context of ultrasound bubble removal. We also report unexpected observations of arrested coalescence between pairs of bubbles forced into contact via acoustic interactions. Overall the comparison of theory and experiments in Carbopol indicates that local yielding is necessary but doesn’t seem to be sufficient to promote bubble removal; and that our analysis may need to account for the gradual nature of the yielding transition as recently established by other groups.


Prof. Amy Shen

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