Wednesday, September 12, 2007

A "sticky" situation

Seabass wanted to know why things are sticky. Since I spent most of high school chemistry trying to figure out how to make my chair lean as far back as possible without falling over, I have no idea.

Apparently it has to do with electrical charges at the molecular level or "an asymmetrical distribution of charge of opposite sign". Dipoles to dipoles. Huh? Is this like molecular or atomic magnetism. Probably not, because none of the articles I read every mentioned molecular or atomic magnetism.

Then there is more chemical based bonds between an adhesive and substrate. These leads you down a quantum electrodynamics rabbit hole. Shit. That's not really helping either. I read a book on quantum physics. It was a hoot, but it felt like science fiction by the end. How am I supposed to divine from this why glue sticks more as it dries?

Okay - BASF's site has an okay answer. Things that are flush stick together well (like two wet microwavable food containers that get accidentally pushed together in the dish rack - I hate separating those things). Glue helps fill the gaps between both objects. I guess I get that. It's similar to suction. But why do flush things stick together? Jelly and peanut butter both fill the gaps in porous peanut butter, but jelly, which seems like it would fill those better, doesn't make bread stick as well peanut butter. There's the old frustration setting in. Unfortunately for me, I can smash, throw or scream at scientific laws. Fortunate for those laws, though.

As Forrest Gump once said "I'm not a smart man". Of course, he followed that statement with something profound - I got nothing though. How do I explain to a 4 year old why some things are sticky, and how "sticky" works.

I can't hardly wait for my friend who majored in materials engineering to give me a sarcastically complicated answer. Don't worry Shadrack - if my head goes all scanners on me and explodes, I'll make sure to post it on Youtube.

And I know the two things you are thinking you're thinking.

One: No, I'm not baked.

Two: Yes, the lame post title was consciously made in an effort to advance the cause of shitty blog post titles everywhere.


Seamus Woods said...

Yeah. Well, the reason why things stick is atomic or molecular bonding, of which there are a few varieties ranging from the strong bonding do to electron donation (ionic) or sharing (covalent), to weak bonding of magnetic dipoles to dipoles (van der Waals)....

But the question he asked is why are things sticky, which is related, but is a bit more interesting of a question. As far as I can tell, gasses and crystals are never sticky. A material can only be sticky when its atoms or molecules can flow and slip past each other like in a liquid. A lot of the things that come to mind when we think sticky are made of polymers, and polymers are just long chains of atoms... so, here goes the 5 year old/poetry major explanation:

Polymers are like tiny, tiny worms. Some polymer worms are really slippery like real worms and can slide and slither past each other very easily. Oil is made out of these kinds of slippery worms, and they work well for keeping things running smooth and quite.
Other polymer worms have rough spots on them that are like Velcro. Some are completely covered in this velcro so that when you mush them all together they are really really hard to get apart. Others just have a little velcro so that they'll slide a little, then stick until you pull them hard enough so they'll slide again. Gum is a good example of something that is made out of these worms with some velcro on them, peanut butter just has a little velcro, the rubber in your bike tires is almost all velcro.

Brant said...

Thanks man - I appreciate that, actually understand it, and will relay it. Then I'll take credit for it ;) Actually, I've been telling him for a few days that Seamus will have the answer. Worms will definitely hold his attention.