Thixotropy in viscoplastic drop impact on thin films

Samya Sen, Anthony G. Morales, and Randy H. Ewoldt
Phys. Rev. Fluids 6, 043301 – Published 30 April 2021
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Abstract

We use high-speed imaging to study the effect of thixotropic aging in drop impact of yield-stress fluids on precoated substrates. Our results reveal that drop splashing is suppressed for “aged” compared to “unaged” samples, indicating that thixotropic breakdown timescales during impact are long enough to affect the dynamics. We propose and test several hypotheses for modifying the dimensionless group [ , Phys. Fluids 27, 043101 (2015), S. Sen et al., J. Fluid Mech. 891, A27 (2020)] to account for thixotropic aging. The main challenge is that the steady flow properties (Herschel-Bulkley model parameters) used in the current dimensionless group cannot be defined or measured for thixotropically aged samples because any deformation inherently rejuvenates and breaks down the microstructure. We find the most suitable hypothesis is to only increase the yield stress (σy, plastic component) based on the storage modulus of aged samples, while keeping the viscous parameters (K or η) constant. The work reveals fundamental insight into rarely studied short-timescale flow conditions with thixotropic effects. These results are important for applications such as fire suppression or spray coating that involve complex fluids of varying degrees of thixotropic aging.

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  • Received 15 October 2020
  • Accepted 7 April 2021

DOI:https://doi.org/10.1103/PhysRevFluids.6.043301

©2021 American Physical Society

Physics Subject Headings (PhySH)

Fluid DynamicsPolymers & Soft Matter

Authors & Affiliations

Samya Sen, Anthony G. Morales, and Randy H. Ewoldt*

  • Department of Mechanical Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA

  • *ewoldt@illinois.edu

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Issue

Vol. 6, Iss. 4 — April 2021

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