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.

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

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:

Gaurav wins Acta Student Award

Congratulations to Gaurav Chaudhary for winning an Acta Student Award for his first-author publication:

Chaudhary, G., D. S. Fudge, B. Macias-Rodriguez, and R. H. Ewoldt, “Concentration-independent mechanics and structure of hagfish slime,” Acta Biomaterialia, 79, 123–134 (2018). DOI link

See the MechSE news article for more details.

Gaurav will officially be presented the award at the Acta Symposium during the TMS conference in San Diego in February 2020.

Plenary lecture in Zürich, Switzerland

Prof. Ewoldt delivered a plenary lecture on “Design of Yield-Stress Fluids” at the 8th International Symposium on Food Rheology and Structure in Zürich, Switzerland, on June 18, 2019.

This especially highlights the work of lab alum Dr. Arif Nelson, and our upcoming paper in Current Opinion in Solid State and Materials Science which was written in collaboration with Ken Schweizer (MatSE, UIUC), Brittany Rauzan (Chemistry, UIUC), Ralph Nuzzo (Chemistry, UIUC), and Jan Vermant (Materials, ETH-Zürich).

PDF of lecture slides available here.


Macromolecules paper: a new concept for stiffness changing soft matter

Our paper “Thermoresponsive stiffening with microgel particles in a semiflexible fibrin network” in collaboration with Schweizer and Braun groups (Material Science, Illinois) is now published in Macromolecules.

We introduce a new paradigm for designing soft materials with large changes of reversibly triggerable stiffness by combining semiflexible polymers that stiffen in tension with microgel polymer particles that massively deswell with heating.

Microgel colloidal particles of poly(N-isopropylacrylamide) (pNIPAM) are embedded in semiflexible biopolymer networks of fibrin. Individual components soften with temperature. When combined, the composite material modulus reversibly stiffens up to 10x in some cases. The developed micromechanical model quantifies the hypothesis of microgel-induced polymer network deformation and is consistent with experimental trends.