How to create an air-free design? I am creating a bottlecap-like design. The design is sealed by rotating the lid. I am adding a chemical to it for an experiment. I would like the inside of the design to have no air circulating to it through the lid tiny spaces.
My design:

Are there any simple solutions I can implement out there? Design-wise, material-wise, or maybe an extra piece?
Are there any simple solutions I can implement out there?

A gasket made of rubber or other elastic or deformable material is probably the best option. Printing one or both of the parts using a deformable material like TPU might also work. Finally, if you don't need to open the unit during the experiment, you could use a sealant like silicone caulk might make sense.