Why does tape distribute static charge unevenly?

[Nienstien]

There's a popular experiment where you get two pieces of Scotch tape and label one top and one bottom. You attach them together on their sticky sides and then pull them apart and they will attract showing that you can get static electricity without friction. Anyhow, when I thought about it I had a couple problems with how this worked out.

How can two like materials distribute charge unevenly? Isn't charge generally governed by the triboelectric series for non-friction events?

Also, the top tape was consistently positive and the bottom tape was consistently negative (Two top tapes from different trials would repel). This rules out a random event such as how the factory applied the adhesive.
I've researched a bit about the adhesive in tape and found that they are either chemically bonding or experiencing dispersive adhesion which involves Van der Walls attraction.

How can adhesives react like this to consistantly provide opposite charges if they are the exact same thing?

This question has been bothering me for a while and I'd like to get to the bottom of it. Thanks

 

[Bill_K]

According to descriptions found elsewhere on the web, in this experiment the TOP tape is stuck to the smooth side of the BOTTOM tape, which explains why they acquire different charges and attract one another.

 

[Nienstien]

I've seen that version too but it works with the sticky sides facing as well which is questioning part. If you have tape you can try it for your self.

 

[Philip Wood]

I wondered if it had anything to do with the Earth's electric field (which is directed downwards). In that case I'd have thought the top tape would become negative and the bottom positive. Anyway, a typical value for the field is 100 volts per metre, which is, I'd have thought, too low to cause enough charge separation for observable attraction. So I think we can rule out this explanation. Pity because it would account for the top/bottom symmetry-breaking.

 

[Meir Achuz]

Do you always pull the top tape off of the fixed lower tape.
My guess is that the moving tape will leave electrons behind and be positive.
Also, the speed of removal may affect the magnitude of the charge.