Rain-X

[SEJohnson95]

I know it's not just E-type related but I'm debating putting Rain-X on the windscreen of my own car. It's coming to uni with me this year and with those long miserable wet motorway runs home in the winter I wondered if it were a good idea?

I've had opinions from both sides, namely that it is apparently a pain in the **** because the water is streaking up the windscreen in between the wiper wipes. (which is what it's designed to do and my car does this anyway with its many layers of glass polish, evidenced by my run along the Fosse Way t'other day. It tipped it down and I didn't need to put the wipers on for a good few minutes) Apparently this is off-putting.

On the other hand it's a well-known product and I've heard a few of you say put it on an E-Type windscreen. Any opinions would be greatly appreciated.

[Heuer]

I always use it on my OTS - E-Type wipers are a tool of last resort!

If you use your wipers they will gradually remove the Rain-X so the trick is to drive fast enough to get the water beading and running up the windscreen. Once it starts running you will not need the wipers until you drop below about 40mph, in which case use intermittent wipe. Most people fail to understand that Rain-X is a two part product - the stuff you polish onto the screen and the special washer additive which replenishes the Rain-X. Used in combination the treatment will last a month or more before you need to re-apply the base product. Give it a try and it also works well on headlights and the other screens. Have to admit I have never bothered using it on my modern cars but that is out of laziness!

This: https://www.rainx.com/product/glass-wat ... treatment/

With this: https://www.rainx.com/product/windshiel ... -additive/

[Gfhug]

the 75-80 mph run along the Fosse Way t'other day.

Honest constabule, I weren't speedin

[SEJohnson95]

Hey, after a day out in Lincolnshire and with an imminent family meal out early evening looming we had to press on! 8) Besides which you E-type owners can't talk, I bet you lot cruise at that speed. My car won't go much faster than that. It needs a sixth gear or 2.88 diff fitting to lower the revs for a start

[Stuart Exelby]

Ahh - yes, that'll convince the magistrate.......

[Paul71a]

well,my E doesnt come out in the rain, but I use Rain X on my Elise all the time; the wiper is bloody useless anyhow due to the curve of the screen.

Great product and works well.

[SEJohnson95]

Ordered some of this stuff:

http://www.ebay.co.uk/itm/171696613292

2-in-1 rain repellent/glass cleaner and also the washer bottle additive to replenish the layer of Rain-X as the wipers sweep over it. I'll let you know how I get on. The screen on my car has quite a shallow angle so the rain should flow off nicely. Now I've just got to get the damn thing out in the heavy rain! Doesn't happen very often.

[christopher storey]

I have used rain X for many years, not assiduously, but when I remember to do it. I have found that it is very effective, and not only reduces the need for the wipers, but also reduces or even eliminates the judder on a drying screen which is so annoying . It is widely used in the aviation industry because it radically reduces the need to use wipers on the approach except in very unpleasant conditions indeed

[trondvo]

I use rain-x much like Christopher here, when I remember I wipe down the screen with the product.

First you have to *clean* the windscreen not just wash it, ethanol and cotton does the job pretty well. Buy a glass polishing kit, polish the screen if neccessary. A well cleaned and polished screen deflect water so much better. Now add rain-x.

When I put rain-x on the commuters in the fall it wears off during the winter but it makes a good difference.

[SEJohnson95]

Thanks for the input gents. The windscreen already has many layers of Autoglym glass polish on and I really noticed it the other day. I haven't done a lot of miles this year apart from in the summer as the car has been at home, so not had a chance to see what the polish does really. It seems everyone on here is in favour anyway!

[malcolm]

Only down side I've seen is that when it starts to wear off, it goes patchy and you get mixed vision. Then you need to remove it all and start again

[44DHR]

I use Rain-X on all our cars and ditto Heuer's comment - especially on the E type - as only using the E types wipers as a last resort.

It is easy to apply and I use it all all windows - side and rear and just let the water bead and run off. There is a "sweet spot" at a particular speed when wipers are not required in light rain conditions. No downsides at all to me. I use Fog-X on the interior glass and apart from their special properties, both clean the windcreen from traffic and internal deposits. I hate a dirty windcreen !!

regards,

Dave

[mooney1el]

Simon (SEJohnson95) - As one chemist to another, I think a good challenge for you would be to investigate: What is Rain-X? How does it work? Are there pitfalls in the application procedure? Could the product be improved?

Hint; think surface tension/ surface energy and "molecular bonding".



Richard Gray

[FRE444K]

I use Gtechiq on all our cars. Longer wearing and no smearing when the wipers are on. As others have said before with any of these products preparation and getting really clean glass is important for them to be effective and lasting.


http://gtechniq.com/products/auto/perfe ... screen-kit

[SEJohnson95]

Simon (SEJohnson95) - As one chemist to another, I think a good challenge for you would be to investigate: What is Rain-X? How does it work? Are there pitfalls in the application procedure? Could the product be improved?

Hint; think surface tension/ surface energy and "molecular bonding".



Richard Gray

OK then, here goes (I hope this makes sense from a chemical point of view and I'm not about to ridicule myself) Take a deep breath everyone!

Background

Glass is composed of a network of silicon and oxygen atoms bonded together, with hydroxyl (OH) groups present at various places, these are arranged in a tetrahedral manner around a central silicon atom to create a large 3D structure. (Glass is amorphous, not crystalline) Image shown below of a representation of the structure after adding Sodium Carbonate which makes the glass less brittle, hence the Na+ counter ions(this is the sort of glass used in windows.)



Hydrogen Bonding

Water is a very polar compound owing to the large difference in electronegativity between its two constituent elements, the oxygen operating what is known as a -I inductive effect on the hydrogen, pulling the electron density through the sigma bonded framework of the molecule. This causes the hydrogen atom to become deshielded , hence it carries a delta+ (slight positive charge) because the electron density is not shared equally between the two atoms in the bond.

Water has some unusual properties for a molecule of its size anyway (high boiling point, its solid form is also less sense than its liquid form, etc.) because of hydrogen bonding. This is the attraction between a de-shielded/electron deficient hydrogen on one water molecule and a lone pair of electrons on another oxygen in a neighbouring molecule, i.e. an intermolecular interaction.




Since glass has hydroxyl groups present, Hydrogen bonding between the water on the windscreen and the surface of the glass can occur, causing a greater interaction between the two, which is why water tends to stick to windscreens.

Polysiloxanates

Rain-X's primary active ingredients are known as polysiloxanates, more specifically Polydimethylsiloxane (PDMS), which is a Silicon based polymer with two methyl groups attached. I.e. two organic functional groups attached to a inorganic chain. This makes the compound very non-polar, so it will be repelled by the water droplets. The monomer is shown below: (one uses many monomer to make a polymer, e.g. styrene and poly(styrene) )



PDMS binds to the hydroxyl group of the glass surface and thus inhibits the interaction of water molecules with the surface of the glass. The two methyl groups provide low surface tension, and this serves to repel high-tension fluids such as water. (Think about what happens when you skim a stone across water, or do a belly flop in a pool, it's the surface tension caused by Hydrogen bonding across molecules on the surface which allows this to happen.)

Glass is also very porous owing to its slightly random 3D structure and the Rain X coating also serves to fill in these pores to to minimise the surface area that the water can make contact with. It increases what is known as the contact angle, and the greater the contact angle,the easier the water will slide off. This makes sense because when the water has a large angle, there is less surface ?holding? onto the water droplet.



This forces the water to bead and roll off the windscreen. Rain X is a type of superhydrophobic coating (water hating), it works at the molecular level to inhibit the interaction.

Adhesion to Glass

Oxygen groups are good at bonding to glass (see above explanation) but only when they are exposed. In a polymerised chain there is a lot of steric bulk (the large amount of space taken up by the rest of the molecule) which reduces their ability to bond to the glass.

In order to make these sort of polymer adhere to glass, the oxygen groups need to be exposed. Consider a similar product to Rain X, known as FAS17. This a fluoroalkylsilane (long groups of singly bonded C-C atoms with fluoro substituents instead of the typical hydrogen substituent as in a simple alkane) with three silyl ether functional groups attached to the Silicon.





FAS17 can be made to adhere to glass better by breaking down the compound with a catalyst (in this case acid catalysed hydrolysis -the breaking down of a substance using water , an organic mechanism that I learned this year), to produce a Silanol (a silicon with an alcohol functional group) followed by a step known as condensation, in which effectively water is to bridge the Silanol and the OH group on the inorganic substrate, in this case the surface of the glass. You then apply a large amount of heat (indicated by the delta H) and polymerise the Silanols, which gives you something like the starting product but now with a more permanent adhesion to the glass surface instead of a coating.

Because the FAS is chemically bonded to the glass it is very hard to remove. This allows the compound to stay active on the windscreen over a long period of time as opposed to the Rain X (PDMS) which can be removed over time by external factors such as wiper blades which is the reduction in effectiveness that you all observe (hence the need for a washer additive to bridge the gap in between applications) however since the compound has been altered chemically through various syntheses, its effectiveness is reduced.




Conclusion

In conclusion, Rain-X and PDMS based repellents have a greater water repellent effect but a much lower binding ability to glass and so need to be replenished. Rival FAS based repellents have a greater lifespan but come with sacrificed effectiveness.

I hope I'm on the right lines with that lot!

Oh and on a final note if I may mention my first-year results briefly (which I received in June but kept quiet about) 87.3% overall, with 89,90 and 86% in Inorganic, Organic and Physical chemistry respectively. The cherry on top was receiving the Harding Prize for the top undergraduate year 1 laboratory marks out of a 120 strong cohort. I'm still a little in shock to be fair! I was never that good at A level

[mooney1el]

Excellent explanation Simon. Hope your enjoyed the challenge. Now when driving down the road with our Rain-X treated windscreens, we can all think of those tiny "water hating" molecules working hard to get rid of that nasty rain water through the wonders of chemistry. And there folks, is what makes a chemist's heart race...understanding :) Before our retirement, my wife and I used to discuss "C's and H's" at the dinner table since she was too a trained chemist.

And congratulations Simon on your achievements

[SEJohnson95]

And there folks, is what makes a chemist's heart race...understanding :)

Right you are there Richard, so many every day thing you apply chemistry to just for the hell of it, it becomes a habit after a while because you just want to understand more about why things work from a chemical point of view. I enjoyed the challenge yes, something to get the mind ticking before the start of another university year in a few weeks time. I wonder if Louise at HQ will let me put that article in the magazine?

[Heuer]

In conclusion, Rain-X and PDMS based repellents have a greater water repellent effect but a much lower binding ability to glass and so need to be replenished.

That's what I said at the start! - do I get a prize?

[PeterCrespin]

And there folks, is what makes a chemist's heart race...understanding :)

I enjoyed the challenge yes, something to get the mind ticking before the start of another university year in a few weeks time. I wonder if Louise at HQ will let me put that article in the magazine?

Excellent article. If you do re-publish I'd make one small change. You wrote in para 3 line 2 of Polysiloxanates:

"...to fill in these pores to minimise the surface area that the glass can make contact with..."

Which should read "to minimise the surface area that the water can make contact with"

Other than that, very readable. Glad you and Richard also cringe slightly when you read silicon and silicone used interchangeably on car forums! If you like chemistry you'd have loved biochemistry - lots of the same stuff with extra slimy bits to play with, some of which could be taken home to eat if you were a hard-up student :-)

My American wife once had a lecture at UNC from a very famous German born but naturalised British Nobel Laureate scientist. His first slide was a picture of a BMW motorbike. His opening remark, which got a good laugh, was "This, ladies and gentlemen, is my [*****] cycle." The asterisks represent the letters of his name. Can you guess who he was (think citric acid or energy production)?

Pete

[Gfhug]

Citric?

How about Lemon?