APS-DFD invited talk (recorded)

Prof. Ewoldt presented an Invited Talk at the APS-DFD Annual Meeting on Nov 22, 2020 (introduced by Gareth McKinley (MIT)):

Title: “Designing Complex Fluids”

Video recording on YouTube (40 min)

PDF of Slides


From the full talk information at APS:

Abstract: A small step away from Newtonian fluid behavior creates an explosion in the range of possibilities. Non-Newtonian fluids can achieve diverse design objectives, but the complexity introduces challenges. This talk will describe these challenges and our contributions to address them. At the continuum-level, careful choice of rheological model descriptions can enable target setting for rheological properties agnostic to formulation and structure. Dimensionless groups also provide a route for microstructure-agnostic understanding, as will be described with yield-stress fluid droplet impact and splashing with applications in wildland fire suppression. At the material-level, flipping structure-to-rheology knowledge to consider the rheology-to-structure inverse problem reveals design strategies. For example, with extensible yield-stress fluids this design-thinking led to the formulation of new direct-write 3D printing inks with unprecedented printing capabilities due to engineered extensibility. This developing design paradigm is applicable to a broad range of applications and material classes and illuminates exciting future research needs at the intersection of continuum- and material-level fluid physics.

Free Virtual Seminar Aug 5 @11:00am CDT

Prof. Ewoldt will give a free seminar as part of the Journal of Non-Newtonian Fluid Mechanics Complex Fluids Seminar Series.

Registration is required to receive the Zoom meeting information. By E-mail, send a plain text e-mail message to <mjrdomo (at)> with the following content:   subscribe fluid-mech-seminar

Other event details below:

August 5, 2020
11:00 CDT (Chicago time)
(9:00 Vancouver, 12:00 New York, 17:00 London, 18:00 Paris, 00:00 Beijing)

Title: Welcome to the playground of MAOS: medium-amplitude oscillatory shear
Randy H. Ewoldt
University of Illinois at Urbana-Champaign


Join us in the playground of weakly-nonlinear rheometry, specifically medium-amplitude oscillatory shear (MAOS). It is now more accessible than ever: for theory, simulation, and experiment.

This talk reviews the developing paradigm of weakly-nonlinear viscoelastic characterization, with particular emphasis on contributions from our group. Weakly-nonlinear excitations are a fundamental characterization technique used in optics, acoustics, heat transfer, and other physical sciences. Yet, weakly-nonlinear rheometry methods have comparatively lagged. Theoretically anticipated for over 50 years, the first complete measurement of weakly-nonlinear oscillatory shear, including all four measures as a function of frequency, was made in 2013 [1]. We have since developed a new frequency-sweep technique that makes experiments much faster [2], facilitating a significant increase in data available for analysis [3]. The MAOS paradigm can be applied to any rheologically-complex material. Recent efforts have demonstrated the ability to infer material-level physics from this continuum-level rheological flow. These efforts include theoretical and experimental work on transient polymer networks [3, 4], polymer melts [5], soft glassy colloidal suspensions [6], and a collaborative work on capillary suspensions [7] which show anomalous power law scaling.

MAOS is a systematic and rigorous step beyond SAOS and a type of “sweet spot” for rheology: nonlinear enough to provide additional information, but still amenable to theoretical predictions. There is still much to explore in this developing area, which will benefit from more researchers measuring and reporting MAOS signatures of theoretical models, simulations, and experiments.


  1. Ewoldt RH, Bharadwaj NA (2013) Low-dimensional intrinsic material functions for nonlinear viscoelasticity.Rheologica Acta, 52(3):201–219.
  2. Singh PK, Soulages JM, Ewoldt RH (2018) Frequency-sweep medium-amplitude oscillatory shear (MAOS).Journal of Rheology, 62(1):277–293.
  3. Martinetti L, Carey-De La Torre O, Schweizer KS, Ewoldt RH (2018) Inferring the Nonlinear Mechanisms of a Reversible Network.Macromolecules, 51(21):8772–8789.
  4. Martinetti L, Soulages JM, Ewoldt RH (2018) Continuous relaxation spectra for constitutive models in medium-amplitude oscillatory shear.Journal of Rheology, 62(5):1271–1298.
  5. Martinetti L, Ewoldt RH (2019) Time-strain separability in medium-amplitude oscillatory shear.Physics of Fluids, 31(2):1–43.
  6. Blackwell BC, Ewoldt RH (2016) Non-integer asymptotic scaling of a thixotropic-viscoelastic model in large-amplitude oscillatory shear.Journal of Non-Newtonian Fluid Mechanics, 227:80–89.
  7. Natalia I, Ewoldt RH, Koos E (2020) Questioning a fundamental assumption of rheology: Observation of noninteger power expansions.Journal of Rheology, 64(3):625–635.


Two open postdoc positions

Two open postdoc positions. Details and application instructions in these PDFs:

Viscoplastic position
(nonlinear rheology, yield-stress fluids, flow visualization, brittle versus ductile mechanics, inspired by plant-based foods for a sustainable future)

JCESR position
(electrolytes, redox-active materials, Newtonian and non-Newtonian viscosity versus conductivity, inspired by flow batteries for grid scale energy storage)

Paper on drop impact of viscoplastic fluids in Journal of Fluid Mechanics

“Properties matter, not the molecules.” – E.L. Cussler.

Our paper on droplet impact with yield-stress fluids on coated substrates is now online:

Sen, S., A. G. Morales, and R. H. Ewoldt, “Viscoplastic drop impact on thin films,” Journal of Fluid Mechanics, 891, A27 (2020). DOI link

We have demonstrated that, as long as the macroscopic rheological flow properties are the same, the microstructural route to those properties itself does not matter. This experimental work demonstrates the generality of a simple dimensionless scaling idea based on forces during drop impact, and its material agnosticity across two vastly different viscoplastic fluids: Laponite clay and Carbopol microgel.


Fig. 6 from the paper: a comparison of impact regimes between Laponite and Carbopol


The supplementary video to the paper, showing the various types of impact behaviors observed in the study.

Gaurav wins thesis award!

Congratulations to Gaurav Chaudhary!

Gaurav (Ph.D. 2019) was selected to receive the Stanley I Weiss, Outstanding Thesis/Dissertation Award in Mechanical Engineering at the University of Illinois.

Gaurav is currently a Postdoctoral Fellow in Applied Mathematics at Harvard.

Check out his thesis here: Mechanics of biopolymer networks, stimuli responsive particle suspensions, and their combinations

And several associated papers on the Publications page.


Review paper in COSSMS: Designing and transforming yield-stress fluids

A big vision of our research is to bring design and rheology together.

We’ve just published a collaborative review of this for yield-stress fluids.

  • Nelson, A. Z., K. S. Schweizer, B. M. Rauzan, R. G. Nuzzo, J. Vermant, and R. H. Ewoldt, “Designing and transforming yield-stress fluids,” Current Opinion in Solid State and Materials Science, 23 (5), 100758 (2019). DOI link Accepted PDF

Yield-stress fluids are perhaps the most utilized rheologically-complex soft materials in our world today. Designing with this behavior enables applications ranging from the everyday to the extraordinary including drug delivery, food products, batteries, painting, surface coatings, biomaterials, concrete, and other scenarios.

The lead author is lab alum Dr. Arif Nelson, written in collaboration with Ken Schweizer (MatSE, UIUC), Brittany Rauzan (Chemistry, UIUC), Ralph Nuzzo (Chemistry, UIUC), and Jan Vermant (Materials, ETH-Zürich).



From Fig. 3: Materials design encompasses design with a material (performance-to-properties), and design of a material (properties-to-structure).



From Fig. 4: Materials design process illustrated using some of our work in direct-write 3D printing.


Uncertainty propagation with generalized Newtonian fluid models

“All models are wrong, and some are useful.” -George Box.

Our new collaborative study with colleague Prof. Jon Freund explores how useful the most common non-Newtonian fluid model really is:

Kim, J., P. K. Singh, J. B. Freund, and R. H. Ewoldt, “Uncertainty propagation in simulation predictions of generalized Newtonian fluid flows,” Journal of Non-Newtonian Fluid Mechanics, (2019). DOI link

Free access until Oct 8, 2019 at this link: