Hydrophobic coating on acrylic/plexiglass, PTFE or other solution?

[artis]

I need to make the surface of a milled acryl/plexiglass surface to have as low of a friction as possible, I am looking online and the only real and also cheap solution I see is the spray aerosol teflon/ptfe, the question I would have is is this the best solution and will it be effective?
I read that commercially the teflon coating is applied to pans by industrial means of preparing the surface mechanically and then applying primer and only then ptfe coating which is then baked, obviously plexiglass can't be subjected to high temps so what would be your advice , would the simple spray on method be effective enough?

My main goal is for the surface to be slippery it will not be subjected to any high mechanical loads or stress it just needs to pass liquids like water etc freely? thanks.

 

[artis]

something like this would probably work for me the question is how would it bond to the acrylic and what should be the minimum surface roughness for the best result

 

[Baluncore]

You are confusing friction between solids with liquid boundary layers.

PTFE coatings will absorb and hold water molecules.

If you machine the surface you have an opportunity to terminate the cut bonds with something hydrophobic.

 

[artis]

@Baluncore Ok my bad it's just that friction is the first thing that comes in mind.

I'm sorry but I'm not sure I understood your idea, so PTFE will not be the best choice here or will it? The way I understand this is that on the microscopic level any surface has some roughness to it, some are more even some less and what materials like PTFE do is they among other things fill in the micro gaps in the surface so that the surface becomes more even on the micro scale and so has less adhesion to fluids like water etc?

But I assume it's not just the mechanical properties but also the chemical ones of the material in question,also once this is sorted I wonder whether it's better to have a rougher surface before such coating or a smoother one?

 

[Tom.G]

Many possibilities found with this search:
https://www.google.com/search?&q=hydrophobic+acrylic+polymer

 

[artis]

I don't find anything in that I could use to coat the surface of my ordinary transparent plexiglass , maybe I'm just dumb I dunno.
If I understand correctly that link shows different kinds of acrylic materials right ?

 

[Tom.G]

Yes, many different plastic compounds that are by themselves hydrophobic, no coating needed. I haven't looked at any of them, and they may be more expensive than what you are currently using. However, you would save the need for a specific surface finish, the cost of the coating operation, and the risk that the coating will degrade or wear off in use.

That's why I mentioned them for your consideration.

Cheers,
Tom

 

[artis]

Yes I've also looked at such materials, notably just having a PTFE plastic instead of a ptfe coating , the problem is I chose transparent plexiglass because it's transparent and rather cheap, PTFE plastic even the transparent one is not really transparent but rather very glossy , so I guess I'm just stuck with trying to find a coating.

 

[Baluncore]

@artis. I think you need to experiment. Once you have finished machining the Plexiglas, scrape it with a razor blade or polish it, while it is whetted with a Windshield Treatment such as Rain-X that contains a hydrophobic compound. The broken bonds on the PMMA surface may bind to the hydrophobic surface treatment to give a more permanent fix.

 

[artis]

So in theory I could polish it while spraying something like a PTFE spray coating from an aerosol can ?
I've never worked with Rain-x but from what I read they achieve the effect not with teflon aka PTFE but with a silicon based compound or something like that, really hard to say which would better suite plexiglass.

 

[Baluncore]

You understand the concept.
The problem is keeping more reactive contaminants away, while breaking the surface bonds to form an activated surface. Those contaminants may include atmospheric oxygen and aerosol propellants.

You need a concentrated surface reactant that is present between the cutter and the new surface being treated. That is achieved with products like Rain-X by pre-coating the surface, before rubbing it with a dry cloth to form the surface bonds.

An aerosol might achieve the pre-coating, but a necessary solvent may evaporate before the process is complete. A poorly bonded surface of hydrophilic compound, coated with PTFE, may not be as good a long term finish as by first eliminating the hydrophilic layer. There are silicon based treatments for cloth that might be applied to mechanically activated polymer surfaces.

 

[artis]

ok this gets complicated fast, so I think I get what you are saying that basically I would want to spray on that windshield coating but not rub it in , then polish the surface with he coating on and only then maybe applying the final coat either of the same chemical or some other maybe.

So you are suggesting that a silicon based compound might work better for the polishing part?

the "mechanically activated polymer surface" was meant as the plexiglass surface ?

 

[Baluncore]

the "mechanically activated polymer surface" was meant as the plexiglass surface ?

Cutting the surface tears the long chain polymer, and so exposes bonds, that activates the surface. If you wet the area with, say methanol, you could terminate those exposed bonds with -CH3. I do not recommend methanol, but it demonstrates what is possible.

Plexiglas = PMMA has been used for aircraft windshields for 80 years, so I expect hydrophobic surface treatments are very well developed.

 

[artis]

I wonder whether it's plexiglass ir polycarbonate that is used in aircraft? because PMMA aka plexiglass is much more brittle and shatters more easily , as far as I know in rally cars they use polycarbonate because you can bend it and it doesn't break or shatter.

I think I know the methanol example because I use another similar chemical called dichloroethane to "glue" two plexiglass pieces together.Ok so the mechanical scratching of the surface exposes bonds but then do the typical agents like Rain-x or PTFE chemically attach to the bonds like methanol? as far as I know no, because these types of chemicals cover the surface irregularities and form a smooth micro surface which is the main reason for the non stick property, right ?

 

[Baluncore]

I wonder whether it's plexiglass ir polycarbonate that is used in aircraft?

PMMA is clear, polycarbonate is not.

The acrylic bubble canopy was used on aircraft such as the Supermarine Spitfire and Westland Whirlwind, which gave better all-round visibility and reduced weight. It is still being used today on most fighter aircraft.

https://en.wikipedia.org/wiki/Aircraft_canopy

Ok so the mechanical scratching of the surface exposes bonds but then do the typical agents like Rain-x or PTFE chemically attach to the bonds like methanol? as far as I know no, ...

It is time you did some research and some experiments.

because these types of chemicals cover the surface irregularities and form a smooth micro surface which is the main reason for the non stick property, right ?

Wrong. The Rain-X compound may fill some of the smallest scratches in the glass, but it is the hydrophobic coating that makes the difference to clarity when moisture is present.