Question: What kind of experiments do you do? Could you give any examples?

Jess Smith answered on 18 Mar 2014:

Yes of course! If you aren’t sure what I do it might be helpful to read my other replies explaining what we are making first!
Day to day I do the following:

Making my samples
This involves taking the rods of hard plastic (that we buy from a special supplier) and turning them into our samples. To do this we use a lathe- a big machine with a spinning blade that can cut very accurately.We make them in to the final shape that we want (wedge, dome, cylinder), then we use a hot-press to heat them up and squash them into discs. After that we put on a coating (which we need to make sure we can control how quickly the sample expands), we either do this by dipping the device into the liquid, or we inject it on to the top (using a mold to make sure we can control it!)

Testing how well it swells:
We put it in water baths (that make sure it is at the same temperature as human bodies- 37.7degrees Celsius) and measure it regularly! We measure the mass using accurate scales (this is so we can see how much water it has taken in), we measure the height and width using calipers (very accurate ruler), and we can use hexane (one of the very few liquids that our plastic doesn’t absorb!!) to measure the volume of the more complicated shapes (we do this by putting it into the hexane and seeing how much the water level rises).

Testing its materials properties: (these are my favourite!)
So we also need to know how and why our plastic is behaving in a certain way. It is all very well saying ‘I have made an expander that expands to this shape over this time frame’ but we also have to answer the question why? what are the molecules doing to allow it to do that? What is the limit of that behaviour? How have I changed the strength of the material? We test these with lots of different experiments. We use microscopes to look at the structure of the plastic (are there any pores? have we changed the direction of the long molecules that make up plastics -called polymers?) We use mechanical testing rigs to pull our samples apart, we do this to check the limit of the strength in a lot of different ways (when we pull it, squash it, hit it from the side, twist it). As we do it we measure how much it has moved, and how far it will move before it will break (we call this strain). We also measure how much force per unit area it took to break it (called stress). We can do this at a lot of different temperatures and also underwater.

I hope this helps! If anything isn’t clear than ask me to explain it 🙂