Saturday, 9 February 2013

Nano-Speculation

I saw a fun video on Boing Boing recently:



The video shows a product called "Ultra Ever Dry", which is apparently an "amazing new nano polymer". It seems to repel pretty much everything with impressive resilience; I gather you're meant to spray it onto things you don't want to rust, or maybe just your boots when you go hiking. Maybe it'd be good for my lab coat...

The website makes some impressive claims:
Dust, dirt, water and other liquids that contain bacteria or radiation never actually contact the surface of the coated material so bacteria and radiation is greatly diminished or eliminated and easy to decontaminate to sterile, if needed.
I'm sure the nuclear industry would be interested to try it!

I was intrigued, so decided to try to find out what it's actually made of. Spoiler: I didn't succeed. My first thought was a perfluorinated polymer - mainly because it sounds snappy, but also because perfluoroalkanes will pretty much repel god. Molecules with many carbon-fluorine bonds have very weak interactions between molecules, and a dense shield of electrons around them, which prevents them from forming strong interactions with solvents and the like.

Which leads to this:
Reprinted with permission from Zhang, Chem. Rev. 2004, 104, 2531. Copyright 2004 American Chemical Society.

What you're looking at is a mixture of water, an organic solvent, and a perfluoroalkane (each with an appropriately -philic dye). Handy lab technique, that one. Also useful in the kitchen; Teflon is a perfluorinated polymer (h/t @V_Saggiomo)

So, what's Ultra Ever Dry made of? They tell us that it's a "nano polymer", by which I understand "polymer we want to market". I spent a whole five minutes scouring the information on their site for clues. There's some useful info on the chemical composition. For a start, apparently it has a "fragrant mint-like odour" and is biodegradable. Application is a two-step procedure, involving two solutions. Otherwise, we learn that it doesn't immediately repel ethanol or skin oils, and is resistant to extremes of pH.

More importantly, we find that the base coat consists of a bunch of reasonably volatile solvents and the magic polymer and additive. The top coat, interestingly, consists of silica and a magic additive in acetone. It may be that my aversion to the word 'nano' is premature; a lot of work on hydrophobic surfaces seeks to create a surface like a Lotus flower, which has a well-defined structure on the nano-scale, often composed of silica. It's this structure, rather than the properties of silica itself, which leads to hydrophobicity.

What surprises me is that, as far as I know, this usually requires special coating procedures. For Ultra Ever Dry, you simply spray on the bottom coat and let it set, then repeat with the top coat. No heating necessary.

Presumably, therefore, the bottom coat acts as an adhesive and provides structure, while the top coat provides the hydro- and oleophobic property. I'm not really sure how you'd get the right kind of structure to achieve this with such a simply application method, so I'm quite impressed.

So how does this work? Leave your wild speculation (or learned opinion) in the comments...

3 comments:

  1. LOL. Like it! Was impressed by this in Chemistry World this month: http://www.rsc.org/chemistryworld/2013/01/super-omniphobic-non-newtonian-fluid-repelling-surface

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  2. That is pretty cool. Bet that's a fun lab - coat the wall in polymer and see if anything sticks. None of this "try pyridine as a catalyst", it's "try custard"!

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