Rain-X changes a filter's transmission

[ulf]

It seams like the active ingredient is non-toxic and environmentally friendly:

https://www.sciencedirect.com/topics/chemistry/polysiloxane

It must be the volatile organic liquid that is flammable and toxic.

[JMC]

My 2 cents worth.

 

The repellent part of Rain-X are claimed to be siloxanes, long chain silicone with Si-O backbones and hydrocarbon sidechains. These types of molecules are oils, and the longer the Si-O chain length the more viscous they become. They are typically very water repellent depending on the side chains used. They are also very sticky and difficult to remove once deposited. They don't form covalent bonds with the surface they are on, unless there is something on the side chains which can react with the surface.

 

The Wired article which is attached is slightly worrying. If there is sulphuric acid in there and there is some left in the product when it is applied then I'm not sure I'd want that sitting on my glass near to any metal filter rings. If there are -OH groups formed from the sulphuric acid, then these will hydrogen bonds with the glass surface and help keep it there.

 

What they are less clear about is whether the layer is continuous. For repelling water droplets the layer does not need to be continuous. As long as any holes in the layer are smaller than the water droplets, the water will have a tendency to roll off, rather than stick to the surface. It's a bit like Gore-tex fabric. That is very hydrophobic and water droplets run off from it, but water vapour can easily penetrate the holes in it, allowing any sweat to evaporate. The Rain-x could well be keeping large water droplets off but still allowing vapour through to the glass.

 

The layer it forms is also likely to be softer and stickier than the glass surface, so any dust particles will have a higher tendancy to be trapped on the surface of the glass.

 

Also, small amounts will be removed every time the filter is polished and will stick to the cleaning cloth, along with any dust/dirt, and be there ready to be redeposited on the next lens/filter you use it on.

[ulf]

Good points Jonathan,

 

The layer it forms is also likely to be softer and stickier than the glass surface, so any dust particles will have a higher tendancy to be trapped on the surface of the glass.

 

Also, small amounts will be removed every time the filter is polished and will stick to the cleaning cloth, along with any dust/dirt, and be there ready to be redeposited on the next lens/filter you use it on.

 

From some Rain-X marketing texts it is also supposed to make it easier to keep the windshield clean and even repel some types of dirt.

I get a feeling that is true to some extent, after two weeks on my car. The dirt rolls away neatly together with the water-beads.

I might be biased after reading the text, I cannot find, looking quickly for it.

 

I am tempted to do some dust test on the different surfaces of my sample disc.

I wonder if domestic dust from my vacuum cleaner will be representative for the test?

 

I hope that carefully washing the filter with a gentle stream of water would be enough, cleaning it, avoiding using any cleaning cloth at all.

[dabateman]

But important question is not all glass is primarily SiO2. As our most susceptible filters, (ug5, ug11, s8612) are not. Has anyone tested a small edge of one of these filters to see if rainx causes clouding?

[colinbm]

Dave I have a whole S8612 under test as mentioned before & here too......

I have it sealed in a clear plastic container now with a little water inside & kept in the cupboard with the water heater for warmth.

With the S8612 is another older piece of BG glass that has been severely corroded before & cleaned but not coated with anything.

[ulf]

Dust test:

I used very fine dust from my Dyson handheld vacuum-cleaner.

The dust beaten from the walls of the HEPA-filter tube.

 

I tried to spread the dust all over the surfaces with my fingertip.

 

There is a very small difference between treated and untreated areas.

The dust sticks slightly better to the treated area, just as Jonathan suspected.

 

The application instructions for Rain-X say that after covering the surface evenly and let it drying well, the excess shall be carefully wiped away.

The remaining few tens of nm maybe isn't very soft and sticky.

 

The dust massaged into the treated surface was also less easy to wash off with just running water.

However when wiping the surface with a soft paper towel the result was the opposite.

It seams like the beading prevent cleaning, but that the treatment makes it easier to wipe clean.

 

I repeated the test after cleaning the surfaces well, this time stating by smearing some skin-fat, from my the side of nose, onto the surfaces and then applying the dust.

When dry wiping this time the results was clearly better on the treated surfaces. It was easier to remove the fat from them.

[Andy Perrin]

I repeated the test after cleaning the surfaces well, this time stating by smearing some skin-fat, from my the side of nose, onto the surfaces and then applying the dust.

When dry wiping this time the results was clearly better on the treated surfaces. It was easier to remove the fat from them.

 

(laughing) Oh my, Ulf, I admire your dedication. Still, it got a result!

[dabateman]

Great tests. Will we see a market blurb from Rain-x that it works even for camera lenses. I am now imaging an infomercial voice taking about this stuff.

It even works with ....

[ulf]

Thanks Andy,

 

BTW, I think the sulphuric acid mentioned in a link above is something used in the manufacturing process to enhance the active component and that it is not present in the final product.

That would be too risky to have in a product spread over many expensive cars.

 

I have done one last test, placing a droplet of Rain-X on pure aluminium to see if it is affected.

The aluminium part was first scrubbed with sand paper to remove the very thin aluminium oxide on the surface.

After wiping off the droplet there were no aggressive etching, only a slightly darker spot on the surface.

 

I have forgotten, but think sulphuric acid react and etch aluminium.

I have no means available to test the ph-value.

[colinbm]

Good news Ulf

Just checked my S8612 coated with 'invisible Glass' similar to 'Rain X' & the old BG glass un-protected, that I placed in a sealed container with some water & placed in the hot water heaters cupboard.

The sealed container is nice & warm & is covered inside with condensation.

The S8612 is nice & clean with no detectable moisture on its surface or any other contaminants.

The old BG glass that has previously suffered badly to this pox is like a wet lolly that you have taken out of your mouth, it is sticky & wet !

I have added a small amount of water & sealed the container again & placed it back in the water heaters cupboard for another week of accelerated testing....

[Doug A]

@colinbm did you ever take the filter out of the cupboard?

Thanks,

Doug A

[colinbm]

8 hours ago, Doug A said:

@colinbm did you ever take the filter out of the cupboard?

Thanks,

Doug A

Yes & was all good.