‘Oobleck’ Fluid Could Produce Smoother Paint


A recent study from the University of Chicago has utilized non-Newtonian fluids that could potentially lead to applications that could lead to less clumping in paint, concrete and other materials. On the flip side, it could also harden materials such as wearable protective gear when hit.

The researchers from the university’s Pritzker School of Molecular Engineering have reportedly used these piezoelectric nanoparticles to investigate the fundamental physics of non-Newtonian fluids.

The work was recently published in the journal Proceedings of the Natural Academy of Sciences.

About the Research

Non-Newtonian fluids, such as Silly Putty, quicksand, paint and yogurt, can change under stress or pressure. The university says that a “hallmark” of non-Newtonian fluids is that their viscosity changes dramatically when the materials are under stress.

According to the university’s release, the team discovered a key role for friction between particles in causing the materials to flip from a fluid to a more solid structure.

“This not only answers long-standing basic questions about the physical origins of these materials, but opens up doors for the design of new non-Newtonian fluids with practical applications,” said Stuart Rowan, the Barry L. MacLean Professor of Molecular Engineering and co-senior author of the paper.

Scientists have reportedly formulated hypotheses about why concentrated particle suspensions change when sheared, or being exposed to multiple forces acting in different directions. These hypotheses mostly relate to how the molecules and particles that make up the materials can interact with each other in different ways under different conditions, but can be hard to prove.

“To understand these concentrated particle suspensions, we want to be able to look at the nanoscale structure, but the particles are so incredibly crowded together that imaging these structures is very hard,” explained postdoctoral scholar Hojin Kim, the first author of the new paper.

For their study, Kim and Rowan collaborated with professor and piezochemistry expert Aaron Esser-Kahn and Sewell Avery Distinguished Service Professor of Physics Heinrich Jaeger. Together, they reportedly developed a technique that measures the change in electrical conductance based on the shear force exerted upon it.

Afterwards, they suspended the nanoparticle in a liquid at such a concentration that it exhibited non-Newtonian properties in the same way as oobleck.

The researchers applied shear force to the top and bottom of the liquid and simultaneously measured the resulting changes to both viscosity and the electrical signals. This then determined how the particles were interacting as they changed from a more liquid to more solid-like material, explained the university.

“We found that friction between particles was critical to this transition,” said Kim. “In this concentrated particle solution, there is a tipping point when the friction reaches a certain level and the viscosity abruptly increases.”

“For any application, we hope we can eventually determine the ideal combination of solvents and particles and shear conditions to get the properties we want,” said Kim.

In terms of applications, the team says that these engineered materials could have customized properties that let scientists control their viscosity under stress. This could include less clumping and clogging of paint and concrete; alternatively, other materials could harden when desired.

“This paper might seem like very fundamental research but in reality, non-Newtonian fluids are everywhere and so this has a lot of applications.”

Now, the researchers are reportedly planning to take advantage of their nanoparticle suspensions to design new adaptive and responsive materials that, for example, become stiffer under mechanical force.


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