How gels and shampoos move: RRI builds a device to see it in action

Researchers at the Raman Research Institute (RRI) have built a new device that reveals how thick everyday fluids like gels, shampoos, and industrial solutions behave deep inside, a breakthrough that can help improve extraction and production processes across industries. 

By showing how these fluids respond to even a single moving object, the method gives companies a clearer way to design materials that flow better, waste less energy and perform more predictably.

Why this breakthrough matters?

This, the team explained, matters because many real-world products and industrial chemicals, from oil-recovery fluids to cosmetic gels, belong to a group known as non-Newtonian fluids and unlike water or cooking oil, these materials do not let objects glide smoothly through them. Their internal structure keeps re-arranging in response to movement. This hidden push-and-pull affects how oil is pumped from underground wells, how a shampoo spreads in hand, and how gels feel and settle on the skin. Until now, scientists did not have a reliable way to watch these changes unfold as they happened. 

The new device changes that. Researchers built a customised set-up inside a rheometer, a common machine used to study how materials flow, by holding the fluid between two cylinders and moving a needle-like probe through it. This allowed them to measure the exact forces the fluid exerted on the probe while simultaneously watching the microscopic changes in real time using in-situ optical imaging. 

This combination of force measurement and live visualisation brought out striking behaviour. At low probe speeds, the fluid acted almost like water — the force stayed constant in time. But beyond a certain velocity, the force suddenly began to rise and fall repeatedly, forming a jagged “sawtooth” pattern. It was a clear sign of what scientists call “chaotic motion,” where the fluid keeps building up resistance and then abruptly releasing it. 

High-speed imaging showed what caused this. As the probe moved forward, the fluid stretched out into a tail-like structure known as a “wake.” This wake grew longer and tighter until it suddenly snapped off, just like stretching an elastic band until it breaks loose causing the sudden drop in force. After each snap, the fluid reformed itself, and the cycle started all over again.

“The design of the custom-built set-up provides the flexibility and freedom to explore many aspects in the context of probe motion to access, measure and reveal the behaviour of complex materials,” said Abhishek Ghadai, PhD scholar at RRI and lead author of the research.

The study shows that this behaviour cannot be captured using traditional bulk measurements, which treat the fluid as a uniform whole. Instead, the findings highlight how local structures — tiny, constantly changing clusters inside the fluid are what actually control how any object moves through it.

“Our study highlights the importance of investigating the mechanics of materials over different length scales to understand complex materials for applications and fundamental scientific interests,” said Prof. Sayantan Majumdar, faculty member at RRI, who led the project.  

How industries could benefit

This method, the team said, can help industries fine-tune materials more efficiently, whether it is improving the flow of drilling chemicals in the oil sector or making cosmetic products that spread more consistently. When industries know exactly how a fluid thickens, thins or resists movement, they can tune their machines to handle it better leading to smoother production and products that behave more consistently for customers, researchers said.