To be able to predict that would be rather complicated. In theory, I think it is because nicotine is H-bonding less to VG or PG than those two are to themselves. So the pure VG or PG is fairly H-bonded, and this pushes the molecules apart a bit (why ice is less dense than liquid water and expands upon freezing: more H-bonds in ice). Introduce nic, and it disrupts some of the VG-VG H-bonds, and they can get closer together. That's the idea I am going on now, but I might be wrong.
So your idea of 50:50 might be correct, but I would think it would be a mole-fraction rather than a volume fraction thing. Since the mol weight of VG or PG are so much less than nic, one gram of nic has a lot less molecules than one gram of VG. Make sense? Well, this is also speculation, and the answer might be something else.
I would think if a
juice is going to contract to "form" the solution, the rate that this takes place would be dependent on the viscosity of the juice made. And shaking can introduce microbubbles, so there are several variables that would need to be controlled out. Too much work for me right now.
My main interest in this is pure nic + PG or VG. Especially at the 100 mg level, and with vendors that dilute pure nic in retail bottles. Less of an issue with DIYers, since a 6% deviation will generally not be a dangerous thing.
