How does plasma coating of textiles work?

Question

I recently heard a podcast episode on plasma, where they mentioned that one of the major applications of plasma physics today is the coating of fabrics, for example for producing rainproof jackets.

What bugs me about it: how do they do it? If the temperature is high enough to turn the atoms of the coating material into plasma, it should be hot enough to also turn the base fabric into plasma.

I tried searching online for videos of how they do it, but only found a handful of PR videos for companies doing the coating, which tended to showcase the water-repellent effect of the finished material, or show people walking around a spruced-up factory. They never showed how it actually works.

So, what is the process behind it, and why does it work? How can we have plasma and a solid object meet, while keeping the solid object intact, such that it even keeps its original structure (in this case, its weave)? And how is it different from applying the same coating material as a gas, without the need to heat it until it has turned into plasma?

Answer 1

Thin film technology, as used to apply teflon-like coatings to fabric, depends vitally on the skills of the practitioner, and those skills represent a clear example of trade secrets.

This is why, for example, a photograph taken of the cleanroom in which antiscratch coatings are applied to plastic eyeglass lenses will have all the nameplates and control consoles of the thin-film application machinery blanked off or photoshopped out.

In general, these technologies work by using excited gas molecules or ions inside a vacuum chamber to mechanically erode a target consisting of a solid block of the desired coating material and then use electric fields to direct the resulting cloud of target molecules more or less in the direction of the piece of fabric or lens on which the coating is to be applied.

It is possible to hold the kinetic energy of the deposited molecules low enough so that the coating goes on at a temperature below the softening point of the workpiece. The plasma deposition conditions required to pull off that particular trick are a closely-held secret.