Hosting the international VPF workshop Oct 8-12, 2023

We are pleased to announce that registration is now open for the international Viscoplastic Fluids Workshop (VPF 9), the 9th installment in the VPF series and the first time hosted in the USA.

Information and registration

Viscoplastic Fluids Workshop (VPF 9)
October 8-12, 2023
The Allerton Park & Retreat Center
University of Illinois Urbana-Champaign (UIUC)


Alexander Rankin Professor, Department of Mechanical Science and Engineering, UIUC

Associate Professor & Gunsalus Scholar, Department of Chemical and Biological Engineering, UIUC

Beckman Postdoctoral Fellow, Beckman Institute, UIUC

European Rheology Short Course Sept 2023

Learn rheology from international instructors from Europe and the USA, including the outstanding faculty at KU Leuven, textbook authors Prof. Chris Macosko (U Minnesota) and Prof. Gerry Fuller (Stanford), and other international lecturers including Prof. Ewoldt (U Illinois).

September 11-15, 2023
Hosted at KU Leuven, Belgium
Registration is now open:

The 19th European School on Rheology, 11-15 September 2023

Soft Matter paper: “Gelation under stress…”

Our new paper in Soft Matter:

Small stress (<1 Pa) can dramatically disrupt gelation.

We report that during temperature-induced gelation, applied shear stress (even below 1 Pa) dramatically changes the gel temperature and the resulting mechanical properties of aqueous methylcellulose (MC). This can lead to catastrophic inaccuracy in relating rheological properties to expected performance if stress-dependent gelation is not considered, e.g. with retention of surface coating in the presence of gravitational stress or extrusion-based 3D printing that must resist gravitational loading.

We use rotational rheometers for the experimental study and a filament network mathematical model to relate the measured properties to microstructural features.

Congratulations to Arif NelsonYilin Wang, and other co-authors!

This work was supported by Corporate R&D at The Dow Chemical Company. Since the completion of this grant, the Pharma Solutions business of Dow, to which this work was aligned, has moved to International Flavors & Fragrances (IFF).

FULL CITATION: Nelson, A. Z., Y. Wang, Y. Wang, A. S., Margotta, R. L. Sammler, A. Izmitli, J. S. Katz, J. Curtis-Fisk, Y. Li, and R. H. Ewoldt, “Gelation under stress: impact of shear flow on the formation and mechanical properties of methylcellulose hydrogels,” Soft Matter, Advance Article (2022). DOI link



Ann Rev Fl Mech: “Designing Complex Fluids”

How can non-Newtonian properties be useful?
What properties are needed?
How can we get those properties?

Rheological complexity facilitates engineering designs across a remarkable range of applications, including human health, energy, the environment, manufacturing, food, robotics, and beyond. Our review identifies organizing principles and emergent methods that enable design of these complex properties to enable future technological advances in such things as advanced flow batteries for grid-scale energy storage, improved fire suppressants for wildfires, and new materials for advanced additive manufacturing.

We review current state of knowledge here:

Ewoldt, R. H., and C. Saengow
“Designing complex fluids,”
Annual Review of Fluid Mechanics, 54, 413-441 (2022). DOI link

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.