-CF2-CF3 ended surface is much less wettable than -CF2- (PTFE). Solid
surface tensions are approximately 6 mN/m for -CF2-CF3, compared with
nearly 14 mN/m for -CF2-. Note that interestingly, -CH2-CF3 has a
surface tension even higher than -CF2-, so you really need that
You can approach achieving a -CF2-CF3 terminated surface with
perfluorinated alkyl chains in place of methyl groups in PDME. Even
better, oriented self-assembled monolayers (I could get
non-nanostructured surfaces with water contact angles of over 170
-SF6 termination is probably even better than -CF2-CF3, but a little
too exotic at the moment...
As far as PTFE goes, go for full fluorination. Wettability drastically
increases with each F that you replace with an H.
Also, aside from chemical property, if you introduce a heavily
nanostructured surface with lots of capillary pores and as little true
surface area comprising your macroscopic surface area as possible, you
will get a very nonwetting surface, far moreso than by any chemical
means. To see this for yourself, take your finger and place a small
drop of water on the underside of a collard green leaf (I guarantee you
it's not perfluorinated). Gore-Tex fabric incorporates a combination
of these properties - capillary pores + fluorination.
Siltech makes various fluorinated silicone resins. PTFE is a
no-brainer. FEP and PFA, are also sold under the name "Teflon", but
aren't quite PTFE, to my knowledge. ETFE is sold as "Tefzel", PVDF as
"Kynar", copolymers of various fluorinated junk "Viton".
Perfluorinated organosilanes and thiols have to be purchased from a
chemical supplier (eg. Lancaster Synthesis). I saw a synthesis for
alkyl-SF6 terminated organosilane in a journal article only.
Polytechforum.com is a website by engineers for engineers. It is not affiliated with any of manufacturers or vendors discussed here.
All logos and trade names are the property of their respective owners.