It’s amazing how widely this type of soft solid is found – we also see them in the natural world, in things like magma.
- Ian Wilson
What do cake batter and a massive, offshore oil drilling rig have in common? The answer lies in a type of material known as a soft solid, which can behave either like a solid or like a liquid, depending upon the stress it is subjected to. Cake batter, molten chocolate, Marmite®, custard and the foamed concrete used in oil wells are all examples of these ‘dual personality’ materials.
Soft solids are non-Newtonian fluids, which don’t adhere to the same rules as ‘normal’ liquids. Newtonian fluids – such as water or cooking oil – don’t change their behaviour as a result of how they have been handled, such as having been mixed or being left stagnant for days. For example, if a bowl of water is mixed for an hour at high speed, it will flow in exactly the same way at the end of the hour as at the beginning.
Non-Newtonian fluids – such as custard, cake batter or foamed concrete – are different. Sometimes they behave like a solid, and sometimes they behave like a liquid. For example, move quickly and firmly enough and it’s possible to walk on custard. But stop moving, and you will start to sink. This is because custard gets thicker or thinner depending on the rate at which you try to move it. This is one way in which non-Newtonian fluids differ.
However, the mechanisms that make soft solids distinctive in this way are complex and still not well understood, making it difficult for engineers to control their properties precisely. Being able to do so would open up a range of new opportunities, whether the goal is a fluffier cake or safer drilling for oil.
There are a wide range of soft solid materials, many of which are present in your kitchen. Researchers in Cambridge’s Department of Chemical Engineering and Biotechnology are attempting to unravel how the structure of one type of soft solid – bubbly liquids – affects their properties, which may enable a far greater degree of control than is currently possible.
Read the full story
Image Credit: Divulgação Petrobras, ABr - Agência Brasil
Reproduced courtesy of the University of Cambridge
_____________________________________________________________