Hi, Jonathan Here. Happy new Year, the winter is here. It seems the extreme weather in the US freezes up many states. California has soaked in a couple of rain storms the last few weeks but finally we got sunshine. For those who are not familiar with us. My name is Jonathan I am the founder of Ascend Sealing Technology and your host in this channel. I believe most of you have the experience to select the proper material for your design. Today, we are going to talk about the chemical compatibility particularly on Rubber Swell In the last episode we discussed about Fluoro carbon elastomer FKM. I will use FKM as an example to explain chemical compatibility. To start with all the boring talk let me show you what is swell. this experiment you will require One beaker Some Acetone A Couple of Fluorocarbon elastomer O-rings Other Optional accessories include: A pair of Gloves A pair of tweezers A Protective Lens Lab Coat Some Kim wipes A ventilated room, such as outside A Solvent and Chemical Respirator And we are ready to perform the test. So first, we measure the original weight of the samples. And the cross -section thickness. Then we pour some acetone into the beaker. Dip the O-ring into the beaker. Start the timer and wait for 5 minutes we should be able to see the difference Now we can take out the O-ring and have a measurement. It is quite obvious that the O-ring has swollen a lot now compare it to the Original O-ring side by side. Take a look So, we showed you the swell phenomenon. And now you will ask me why and how this happended? Now it’s time to talk about the interesting science behind the theme. In the last episode we have discussed the FKM type and we will use the most common FKM type, A-type, as the example A-type contained around 40% Vinylidene Fluoride VDF and 60% of hexafluoropropylene HFP randomly mixed in the rubber polymer chain. VDF and Acetone both are polar molecules that polar solvent will diffuse in polar rubber and can be easily mixed together. You may ask why? Rubber is a solid object, how does Acetone dissolve into FKM? First, these monomer are in a fluid state before polymerization. After polymerization the molecules get heavier but still have fluidic property. And then, with curing or crosslinking, the polymer chain formed a 3D network that becomes a highly viscus fluid but it is still fluid. Let’s bring up the definition of “fluid”: a substance that has no fixed shape and yields easily to external pressure Such as a gas or a liquid. So take your O-ring apply pressure on it, yes, squeeze it. The rubber is just a viscoelastic material by definition. We will explain viscoelastic later. Just note, the rubber will still remain with a fluidic characteristic, which is good for now They will remain in a fluidic property and they will have thermodynamically mixed with other fluids So the solvent, such as the experiment with Acetone will diffuse into the FKM rubber 3D network This is because Acetone is a polar solvent and the 40% of FKM is a polar monomer VDF Polar solvents will dissolve in polar rubber such as A-type FKM. Non-polar solvents will not dissolve in polar rubber such as A-type FKM. Well … there is a simple way to explain it. Sure, Consider this Soda water(Polar) as our FKM rubber. I mixed it with some whiskey That is because alcohol is soluble(miscible) to water. My rubber volume has increased into a cocktail volume And I’ve got a super extravagant highball cocktail! Your friends at Ascend Sealing remind you to drink responsibly In the other case, the soda water is our rubber. I pour some Italian extra virgin olive oil into my soda water. Due to Olive oil’s in-soluble or immiscible properties my rubber repels the oil and the volume remains the same. The olive oil can be fuel, gasoline, or natural gases. Even though the O-ring swelled a lot, a fluid diffusion is a physical mixing there is no chemical reaction involved. Thus, drying out the FKM O-ring lets the acetone evaporate the O-ring will return almost to its original size However, the dimension back to original does not mean everything is the same. The rubber was molded with high temperature to increase the polymer chain randomness. We swell the O-ring and let the solvent evaporate in room temperature that will change the polymer conformation and 3D structure. Typically, this will result in a slight change of the physical property and it becomes slightly harder. In summary, Rubber components are often exposed to a liquid that has some degree of thermodynamic compatibility or partial solubility. When two liquids are mixed together, they can be totally soluble partially soluble, or totally insoluble. We avoid elastomer selections based on totally soluble properties unless we want to make a rubber solution We prefer totally insoluble properties but it is often too costly or impossible to make. We must therefore learn to design with partial soluble properties. We’ve listed some common synthetic rubber’s polarity for your reference. I hope you have enjoyed this video. if you liked this video, please click the “like”icon and smash the subscribe button to support our channel. Hit the bell icon so you won’t miss any episodes, because sometimes YouTube intentionally will not let you know about new episodes. Thanks for watching, we will see you next time.