Material of the Month
The month’s material is something most of us are familiar with, having used for various purposes like sealing the threaded pipe connection on the shower head at home or perhaps an air line connection in the garage or at work.
PTFE (TeflonTM) was invented by accident by Roy J. Plunkett at DuPont in 1938. It found its way into cookware starting in 1945, as a “no stick” surface. PTFE tape is well known for its sealing function on fittings, and also for the fact that the material has an extremely low coefficient of friction, giving it a slippery feel. PTFE doesn’t become brittle, even down to -240°C, and keeps its properties at temperatures over 500°C. It is also remarkably unreactive, and can’t be dissolved by the most corrosive and aggressive solvents, except molten sodium and fluorine gas under pressure 1. All these properties, of course are due to its chemical structure. But what about its physical structure?
These images of PTFE tape were acquired in a scanning electron microscope in Secondary Electron Imaging Mode to show the sample’s surface morphology. Because PTFE is also a great electrical insulator, the sample was sputter coated with a thin layer (approximately 3nm) of iridium metal to provide surface conductivity and prevent charge buildup on the surface from the incident electron beam (that degrades the electron images). This structure of “islands and filaments” is very characteristic of flexible PTFE tapes and tubes.
It is interesting to note that since the material is made up of “light” elements (carbon and fluorine) and, even at a reduced beam voltage (10KeV), some of the electron beam passes through some areas of the islands, and the underlying filaments are visible. It’s just another material that’s interesting to look at up close!
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1 Lemelson-MIT Program, Massachusetts Institute of Technology (2000, July). Roy J. Plunkett, Teflon. Retrieved from http://web.mit.edu/invent/iow/plunkett.html