I think the spell represents sublimation, which doesn’t convert mass to energy (actually requiring energy, but I guess that’s the “magic” part of the spell). So the paladin’s mass (body, armor, weapons, etc.) would remain. I’m not sure how to decide how big the bottle needs to be (though, likely not very large), I just don’t know how the party is reasonably throwing the bottle. It’s similar to picking up the paladin (in their normal, physical form) and trying to throw them across the room.