Chemistry of Teflon

[sbutk]

Someone with a background in chemistry might need to answer this one for me. Teflon (PTFE polymer) contains fluorine atoms bonded to a carbon backbone. It seems to me that the material ought to be able to participate in hydrogen bonding, such as with another material such as H2O (water). Yet water droplets roll around on a Teflon sheet just like no special bonding takes place. Can you explain this?

[Gef]

Hydrogen bonding only occurs when a highly electronegative atom (such as fluorine, nitrogen or oxygen) is bonded to a hydrogen atom resulting in a strongly polarised bond. The bond between carbon and fluorine is not polar enough.

[sbutk]

OK... but what about the oxygen that the H2O's hydrogen is bonded to? i.e. ...C-F --- H-OH Hydrogen would be between the electronegative fluorine and electronegative oxygen. Doesn't that count?

[AllYourBase]

The bonding between the C-F is too strong for it to be even interested in considering looking at the H or the O in water in the form of a hydrogen bond. Fluorine in the ionic form is one of the most reactive elements known, which means it also forms VERY tight bonds, very rapidly to other elements, in this case, the carbon. What we all want to know of course, is how do we get teflon to stick to the pan?

[sbutk]

Good answer, thanks. Out of curiosity, can you give an example of fluorine that DOES participating in H-bonding? Because teachers and professors drilled into our minds that H-bonding can occur with atoms of the elements F, O, and N. And I've read that one way in which Teflon is stuck to a pan is by first etching the pan surface. The Teflon is then allowed to polymerize inside the grooves.

[thekraut]

water sticking/not sticking is not only a question of chemical bonding. its a question of relative surface energies/tensions. in order to minimize the overall surface energy, a three phase system like teflon/water/air will automatically aquire the state with the minimum surface energy, in this case maximum surface air/water and minimum surface water/teflon. so even for a certain amount of adsorption energy between water and teflon, the surface is just not big enough to keep the droplets in place. it's the same thing as mercury on almost every surface. oh, and there's a difference between atom bondings like the C-F and the bondings between different molecules because of electronegativity/partial charge. so i don't see why there shouldn't be an attractive force between the F and H atoms. I think the fact that it'0s used for pans is not so much that its particulary non-stick (as compared to other plastics) but its thermal stability. maybe PE is non-stick as well but can'tbe used as it melts at too low temperatures.

[sbutk]

Good point. H2O has its own peculiarities. That's probably the missing link that I've overlooked.

[Gef]

For sbutk, no it doesn't count as the hydrogen must be bonded to the fluorine. SimonC and thekraut are both talking rubbish and don't know much chemistry. Teflon does not stick to the pan but is held there mechanically.

[thekraut]

talking about rubbish, gef: F does not have to be chemically bonded to the H for having an attraction between them. Teflon is definitely NOT non-stick because its chemically inert enough to prevent any reaction with other materials, because so is stainless steel and enamel - and those two are very stick. or am I being stupid again, smarta$$?

[Gef]

Sorry to thekraut I did not mean to offend. However, I do know what I am talking about. Hydrogen bonds can only be found between a hydrogen atom in one molecule and a highly electronegative atom such as fluorine, oxygen or nitrogen in another molecule. For this to happen the hydrogen atom must be covalently bonded to either F, N or O (and sometimes Cl) producing a polar covalent bont in which the hydrogen atom has a slight positive charge and the other atom a slight negative charge. The hydrogen atom in one molecule is then attracted to the electronegative atom in another molecule producing the hydrogen bond. For example, in water, the hydrogen bonds are formed between the hydrogen atom of one molecule and the oxygen of another.

[thekraut]

no offence taken (well, maybe a little bit.... at first) and Totally agree with you on the hydrogen bond stuff. but does not explain at all why teflon is non stick, does it?

[Gef]

Thanks for your forgiveness kraut. I've just googled over 3000 sites and can find no good explanation of why Teflon is non-stick. I have a feeling that nobody really knows - have a look at http://www.chemguide.co.uk/organicprops/alkenes/polymerisati on.html and scroll right to the bottom of the page.

[iloveerica]

actually i have a question???? about chemistry...ha ha well.... Forced attractions between polar molecules are known as what? please help big test tomorrow.. thanks

[sbutk]

"Forced" attractions? The only things that come to my mind would be generally termed "dipole-dipole" and dipole-induced dipole" interactions. ...Anybody else?