A collaborative study by IIT researchers shows that adding tetrapod-shaped nanoparticles to certain synthetic plastics can make them less sticky and easier to process
The usefulness of plastics lies in what their name implies. They are moldable, stretchable, and can be reshaped into almost any form. This versatility comes from the structure of long molecules called polymers, which constitute them. However, many synthetic plastics composed of heavy and long molecular chains are extremely thick in the molten state. Scientists describe this as having high viscosity. As a result, making such plastics flow during processing can be difficult, energy-intensive, and hence costly.
In a promising breakthrough, a recent collaborative study by researchers from the Indian Institute of Technology (IIT) Bombay, IIT Madras, and IIT Kanpur has shown that mixing tetrapod-shaped nanoparticles—tiny particles resembling the four-armed concrete structures used as sea wave breakers—can make certain polymers flow more easily. These polymers typically have high molecular weights and long chains that are prone to forming knots, yet the tetrapod-shaped nanoparticles help reduce flow resistance. The team demonstrated this effect using the polymer polystyrene (PS). The research was led by Prof. Mithun Chowdhury, who heads the Lab of Soft Interfaces at IIT Bombay, with collaborations from Prof. Anindya Datta (IIT Bombay), Prof. Tarak K. Patra (IIT Madras), and Prof. Sivasurender Chandran (IIT Kanpur). Jotypriya Sarkar, Mithun Madhusudanan, Harshit Yadav, Dr. Fariyad Ali (IIT Bombay), and Dr Sachin M. B. Gautham (IIT Madras) did much of the experimental work and analysis.
“This study opens a pathway to potentially lower processing energy in the future, if we can mass synthesise precisely-shaped sustainable nanoparticles,” says Prof. Chowdhury, highlighting the study’s potential impact. The inspiration for using tetrapods came from a casual moment. “During a walk along Marine Drive, we saw the large concrete tetrapods used to break waves. That sparked a question: what if we used tiny versions of these shapes in thick polymer fluids?” recalls Prof. Chowdhury. Prof. Chowdhury thought of testing out tetrapods because of their unusual geometry. Nanoparticles of other shapes, such as spheres or rods, are known to increase viscosity rather than reduce it.
This curiosity quickly turned into an experiment because Prof. Datta’s lab at IIT Bombay had been synthesising such nanoparticles for some time. Prof. Chowdhury and his PhD student Jotypriya Sarkar obtained cadmium-selenium (CdSe) tetrapods from Datta’s lab and tested them by carefully incorporating them into polystyrene. The physical and rheological—concerning how a material flows, how it deforms under stress, etc.—properties of polystyrene are well-understood. Thus, using polystyrene enabled the researchers to clearly tease out changes in flow behaviour caused by adding the nanoparticles. They also ran control experiments with spherical and rod-shaped CdSe nanoparticles for comparison and noted that only the tetrapods improved flow, whereas the other shapes made the polymer more viscous and resistant to flow. This suggests that the observed decrease in viscosity is due to the particular geometry of the tetrapods. Additionally, the researchers showed that adding nanotetrapods did not compromise the mechanical and thermal integrity of the polymer.
To probe the physics behind this difference, the researchers employed molecular simulations based on the Kremer–Grest bead–spring model, which realistically captures nanoscale polymer behaviour. Prof. Patra and Dr Gautham at IIT Madras conducted the relevant simulation-based studies. “The simulations showed that the inner curvatures of a tetrapod create regions that long polymer chains find unfavourable to enter,” explains Prof. Chowdhury. “This causes the lowering of the number of polymers around the nanotetrapod and thereby lets polymer chains slide past one another more easily.” This geometry-driven effect is not observed in short-chain polymers or simple liquids, he cautions us about generalising the results.
The findings also suggest that nanoparticle shape could potentially be used to tune how plastics flow. “Many applications, like coatings, adhesives, or 3D printing resins, require specific viscosity for shape retention or load bearing. There are plenty of examples of nanoparticles increasing viscosity, but our study shows it can go both ways. Compact particles like spheres or road can thicken materials, while branched geometries like tetrapods can make them thinner,” explains Prof. Chowdhury.
The team is currently exploring ways to scale up the process for preparing polymer-nanoparticle composites and adapt it to different types of polymers. Key challenges remain, including large-scale nanoparticle synthesis and replacing toxic materials such as cadmium with more environmentally friendly alternatives. “Future work will extend this to other polymers and more complex nanoparticle geometries,” adds Prof. Chowdhury. In the future, the group aims to develop models, using AI or machine learning techniques, to predict the behaviour and flow patterns of polymer-nanoparticle composites based on nanoparticle geometry.
The research also highlights how curiosity-driven collaboration across IITs can lead to discoveries with industrial promise. “This project truly grew out of collaboration,” says Prof. Chowdhury. He continues, “At IIT Bombay, our Lab of Soft Interfaces led the experimental and rheological studies, spearheaded by my PhD student Jotypriya Sarkar, while nanoparticle synthesis took place in Prof. Anindya Datta’s lab. Prof. Tarak Patra’s group at IIT Madras handled the molecular simulations, and Prof. Sivasurender Chandran from IIT Kanpur contributed conceptual insights. The synergy between precise experiments and computational modelling was essential; neither could have revealed the full picture alone.”
Reflecting on the journey, he emphasises that such teamwork thrives in an atmosphere of mutual curiosity and trust. “We are more friends than mere collaborators,” he says. “Curiosity-driven, intellectually stimulating work needs a friendly and fun space, something we made sure to maintain.”