[tsmith]

I was looking into what made RainX worked and saw that the composition of RainX is as follows:
Rain-X's primary active ingredient are polysiloxanates, the primary one being hydroxy-terminated polydimethylsiloxane.[16] The polysiloxanes have functional groups that bind to the hydroxyl group of the glass surface.

Is there a polysiloxanate that would bind to rubber instead of glass? Essentially causing water to run off of rubber like it does the glass windshield with RainX?

[zaphraud]

I was looking into what made RainX worked and saw that the composition of RainX is as follows:
Rain-X's primary active ingredient are polysiloxanates, the primary one being hydroxy-terminated polydimethylsiloxane.[16] The polysiloxanes have functional groups that bind to the hydroxyl group of the glass surface.

Is there a polysiloxanate that would bind to rubber instead of glass? Essentially causing water to run off of rubber like it does the glass windshield with RainX?

the thing about rain-x is that it imparts a hydrocarbon stub's hydrophobicity to a silica-based substrate (in this case, glass) by being able to stick down to it with the "-O-Si-O-Si-" chain side "down" (where if nearly perfectly matches the silicon dioxide substrate) and the methyl groups pointed "up".

Rubber probably already has that property. The reason water doesn't roll off it is likely either that its simply not smooth enough, or that the rubber contains additives that make the polymer more light resistant or ensure it retains flexibility.

So really, what you are looking for is some kind of substance that is totally hydrophobic but also won't dissolve the rubber. That last part is critical; the fact of the matter is that repeat use of even regular "Armor All" (as of 2000 anyway) eventually produces a quite noticeable discoloration of many rubber and plastic surfaces. They still teach that oil leaks in cars will have a severe life-shortening effect on the car's rubber hoses, so this is a general problem.

Another complication is that the wheels are going to be exposed to the elements a hell of a lot faster than the glass window, and most days, are going to get quite a bit hotter too. So you have to consider if whatever your additive breaks down to is going to interact with the rubber as well - My hunch is that this is the part where "Armor All" starts to be a problem because the advice for people who use it and don't want to quit is to keep the coating fresh and shiny, and those that do definitely have better luck than those who don't, which is at least suggestive that they aren't simply trying to sell the stuff faster and actually are saying something helpful.

Hmmm... I hope to see lots more replies here because I have a hunch there's a novel solution to give shiny black tires under all conditions that hasn't been marketed yet.

[tsmith]

I am trying to understand why some rubber products will become slick when exposed to the elements (rubber bouncy ball that my son leaves in the backyard for months) when others don't (car tires, for the most part) and even some rubber products will become sticky when exposed to elements.

[zaphraud]

I am trying to understand why some rubber products will become slick when exposed to the elements (rubber bouncy ball that my son leaves in the backyard for months) when others don't (car tires, for the most part) and even some rubber products will become sticky when exposed to elements.

Many synthetic rubbers (polymers) also have plasticizers added to them to increase flexibility, these can be leeched out and produce either a sticky surface or a hardened, more water resistant one, depending on the polymer and the plasticizer. Some plasticizers can also decompose into something that is quite gummy over time.

Chances are that synthetic car tires don't have any of the typical plasticizer in them because the plasticizer must remain evenly dispersed over a wide range of temperatures and stresses, or the tire fails. To see something like this in action, some cheap pieces of plastic, went bent back and forth, will concentrate their coloring agents in one spot, leaving white polymer at the bending point.

[marquis]

There are a number of silicone (that's the common name for the polydimethyl siloxane) products used to bond to rubber.  Some are used to cross link the rubber.  Many of the rubber supply houses could give you more information.

I think there is a better way to proceed.  You will find many pharmaceutical stopper manufacturers are using plasma coatings to give rubber the properties you need.  These are often done using PTFE (tradename Teflon) and other materials.  There was some progress with parylene materials, as well.  The parylene doesn't require as high a vacuum.

If the rubber you are using is based on polyisoprene (natural rubber or its synthetic equivalent), you can make it much "slicker" by chlorinating it with bleach. This is a touchy process.  I need to emphasize this- be aware that the clorination only works on polyisoprene. 

Hope this helps and good luck.

[tsmith]

That helps. What I am actually trying to do is to keep rubber from getting slick, in other words keep the grippy nature of rubber even when exposed to UV and rain. In addition I would like to have a way of changing rubber that has been changed from grippy to slick back to the original grippy nature. If that makes any sense. Both a preventative and also a way of refurbishing the material.

[zaphraud]

Its been brought to my attention that the white coloring in repeatedly bent pieces of simple plastic (PE) not designed to bend, is not just from coloring agents in the plastic moving around, but also (primarily, even) repeated failures in the polymer chain itself that end up giving it optical properties more similar to paraffin. Oops.