I spent a while recently flipping the lid of a cosmetics bottle open and shut. This was the kind of lid that you typically get on shampoo bottles, ketchup, honey and so on, where the bottle top, hinge and lid are all fabricated as a single piece of the same material. This particular one was sealed simply by a stopper on the inside of the lid popping securely into a hole on the bottle top.
Try to find one of these lids yourself, and take a careful look at it, thinking about the properties that are needed to make it work. The lid needs to be hard enough that it can’t be scratched easily, as well as both strong and tough enough that it won’t break if you drop the bottle on the floor. It needs to be elastic enough that the stopper itself can pop in and out of its hole, making a secure seal. The hinge also needs some elasticity so that it can stretch a little to open and close, but it must not be prone to fatigue (progressive weakening and eventually breakage) when it is opened and shut many times. It needs to be possible to manufacture the whole lid in a single piece, including the hinge, because there are no joints. This is likely to have been done by injecting fluid polymer into a mould with more than one entry point for the fluid, perhaps one on the lid side and one on the bottle top side with the flows merging completely where they meet.
The combination of properties that make a specific formulation of a particular polymer suitable for this application did not arise by accident, or just ‘picking something off a shelf’; it is a careful process of optimisation, getting the right balance between all these aspects of the physical properties of the material. And that cannot be done without a proper understanding of why materials behave as they do, right down to the atomic level.
Without the discoveries and advances in materials that were made from the mid-twentieth century onwards, we would not have our smartphones, our electric vehicles, our high-performance sports gear. However we have to fabricate all of our modern materials from the range of elements offered to us by the Periodic Table (a relatively small number of elements, considering how much we are able to do with them). Understanding how materials fit together at the atomic scale also allows us to appreciate the skill and effort that has gone into designing and manufacturing even quite mundane items.
I came into Materials Science out of a fascination with materials at this atomic level; the way that atoms organise themselves into the structures, materials and artefacts that we see and use in the world around us. My particular specialism has been electron microscopy and diffraction, which has given me the opportunity to see materials at a scale far below the resolution of the human eye. Materials of all kinds are extraordinarily beautiful at the microscopic level, and this atomic world is full of wonder and possibility: where might discoveries in this area lead us next?
Dr Erica Bithell