Many phenomena and materials that are familiar to us are actually scientific mysteries. Reinforced rubber has long been on this list: why is it so efficient in so many applications, from aircraft tires to industrial seals and medical devices?
A team of engineers believes they have finally found the answer — and the solution unifies several theories about the resilience of reinforced rubber: essentially, it fights against its own incompressibility, explains .
In a new one published this week in the magazine Proceedings of the National Academy of Sciencesengineers at the University of South Florida (USF) identify the physical mechanism behind this resilience.
This composite material, which is technically a combination of rubber and “carbon black” particleshas remained practically unchanged over the last century, thanks to its high rigidity and resistance.
The new study concluded that adding microscopic particles to rubber transforms this intrinsically soft material into something “strong enough to support the weight of a fully loaded jet“, according to one from USF.
This property of the material results from a discrepancy in what is called Poisson’s ratioa metric that defines the way materials change shape when they are stretched.
It works, it works
From a chemical point of view, rubber is a type of polymera system of large, interconnected, chain molecules. This structure gives the rubber its characteristic elasticity and, consequently, its wide use.
In 1944, researchers formally documented rubber’s tendency to become more rigid with the addition of microparticlesalthough the phenomenon itself was already known previously.
This reinforced rubber formula is so effectivewhich scientists, engineers and industry stakeholders trusted her for almost 100 yearsthe researchers explain in the article. However, scientists never reached a verdict on the reason this formula works so well.
“How is it possible that we have used it for 80, 90, 100 years and never really understood how it works? Everything was based on enormous processes of trial and error”, he says David Simmonssenior author of the study and engineer at USF, in the statement.
“Tire companies can purchase many different grades of carbon black… and simply have to resort to trial and error to understand what is worth paying more for and what is not,” explains the researcher.
Gather the puzzle pieces
Simmons explains that the debate about this mechanism has been going on for at least several decades. Some have argued that the particles formed networks additional chain-like particles within the rubber, while others proposed that the particles merely forced the rubber to stretch more by taking up additional space.
To determine which of the ideas best represented reality, the team virtually recreated the molecular structure of the reinforced rubber. They carried out around 1,500 molecular simulations involving hundreds of thousands of atoms.
The team found that previous theories were not necessarily wrong. Each hypothesis alone could not capture the full picturebut all together — particle networks, adhesive interactions and space-filling effects — contributed to the final result.
According to the new, more comprehensive framework proposed by the team, rubber intrinsically resists changes in volume. Imagine stretching an elastic band: the elastic becomes thinner as it stretches, but the total volume remains constant.
When carbon black particles are added to form reinforced rubber, the composite material “fights against itself” and increases in volumerigidity and resistance.
The particles prevent the rubber from becoming thinner when stretched, so the rubber is forced to increase in volume. This phenomenon is called Poisson’s ratio discrepancy, in which the rubber essentially fights against its own incompressibility.
The findings should help manufacturers move away from trial and error in creating tough rubber, the team says.
In addition to increase industrial efficiencythis knowledge could help with safer construction of critical infrastructures, such as power plants or aerospace systems. A, which 40 years ago took the lives of 7 astronauts, originated from a rubber gasket it got too coldSimmons points out.
“Many energy systems, power plants, have rubber components. We’ve all had a garden hose that started to leak because a rubber gasket gave way. Now imagine this happening in a power plant or in a chemical factory”, concludes the researcher.
