All the teflon frying pans I have seen are aluminum. The reason aluminum doesn't rust is that a thin layer of aluminum oxide forms on the surface of the metal. If you blended, copolymerized, or better yet were able to sythesize a block copolymer of TFE with a monomer that would hydrogen bond with the aluminum oxide ie. vinyl alcohol. You could pour a hot homogenous mixutre on the aluminium and upon cooling the mix would microphase seperate with the OH moeity concentrating on the metal surface and the CF migrating away from it. H-bonds are stronger than Van Der Waals interactions and the in the case of the copolymerizations the two components are chemically bonded. Even in the blend case entropy would probably be such that chains of CF would remain imbeded in chains of OH. It is hard enough to get small molecules to crystalize quantitatively. Consequently, once the mixture has "set-up" on the metal surface heating would not return the coating to homogenaity. As each phase of the polymer would rather stay separated OH-Al CF-not Al or OH than recombine OH-CF.That is a very good idea, using the aluminum's own corrosion to aid in binding PTFE to the pan. A copolymer would probably work better than the blend. The blend woul dindeed tend to phase separate. You see, polymers don't gain very much entropy on blending, so they don't blend unless there are strong enthalpic interactions. There would not be such enthalpic interaction in the blend here, so PTFE and polyvinyl alcohol would probably phase separate. Copolymers are a better way to go. Random copolymers might actually work better than block copolymers because even "random" copolymers have blocky segments. Random copolymers have more blocks per chain than true block copolymers, which means there are more ties between the frying pan surface and the polymer layer.
Thanks for your idea, Ben!
1. Prepare pan by sandblasting.I think it's quite clear, Adam, from reading the reference you cite that some sort of compatiblizing third component is used to make PTFE bond to frying pans when the DuPont source says:2. Add primer layer, eg [-CF2-C(something sticky)2-]n. PTFE will stick to itself quite well (PTFE tape). My guess is that if you get a polymer that can present a layer of fluorinated polymer to PTFE, PTFE will stick to that as well.
3. Spray/pour over PTFE. It will stick to the primer layer.
We know that the process involves grit-blasting or etching from DuPont themselves ( http://www.efni.com/~paradox/teflon/email.htm) - I suspect that this helps with the sticking of the primer layer
"Although we can't divulge the ingredients of our products, we can say that a blend of an organic mix and PTFE (polytetrafluoroethylene) allows this process to take place."A semi-fluorinated homopolymer as you suggest is a good possibility. Another candidate would be a copolymner of tetrafluoroethylene with some other monomer.
However, as far as surface etching, the DuPont source says they used such techniques at one time, but they go on to say:
"DuPont has recently introduced new patented technology in the primer which allows TEFLON(R), SILVERSTONE(R), and SILVERSTONE(R) Xtra to be applied over a smooth substrate."So it seems they've figured a way to put this stuff on without etching. Does anyone have any ideas about what that might be?
I must stress here that the surface etching would be used not to make PTFE stick to the pan, but to make the compatibilzer stick to the pan. This in turn would allow PTFE to be bonded indirectly to the frying pan. But without a compatibilier, etching would only increase the repulsion between the metal pan and the PTFE.
Thanks for your response, Adam!
I think that the surface of the PTFE is etched with sodium to remove some of the fluorine atoms and produce free radicals. The polymer is then able to bond to the metal at these sites.
Good thinking, Craig! Sodium metal is one of few things that will actually react with polytertrafluoroethylene. Thanks for your response!
From what I have heard you use a composition of PTFE with a strong oxidizer (Chromium tri-oxide). The first layer is sprayed onto the pan with a high percentage of CrO3 and each subsequent application you use a lower percentage of CrO3. When you reach your final layer you have an almost pure layer of PTFE with a color and metallic flakes added to conceal the previous layers.
Sounds pretty cool to me!
The metal of the frying pan must have texture where the teflon will be able to stick. You must melt the teflon at very high temperatures. Once the teflon is melted you would let it "settle" into the ridges on the frying pan.
Roughening surfaces helps when you want an adhesive to stick to a surface. The reason this happens is that roughening the surface increases the total area of the two surfaces that will be in contact. Interactive forces between two surfaces increase with increasing surface area of contact. What this means is that if two surfaces are attracted to each other, they will be attracted even more strongly when the surfaces are roughened.
However, if the forces are repulsive, as is the case with PTFE and steel, roughening thesurface will only increase the force oftherepulsion between the two surfaces. So roughening the frying pan will make PTFE stick even worse than it does on a smooth surface.
Thanks for you question, Dietrich!
