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Cross post: http://chemistry.stackexchange.com/q/4377/22

Last week I was discussing with a friend how we thought the stripeless cleaning of windows is achieved when using a cleaner like Windex Glass Cleaner as opposed to just using hot water, in which case you do get stripes left behind.

At first we thought that the stripeless nature was caused by surfactants in the cleaner that allow the (polar) dirt on the windows to be collected in the water through micellation. However, when we use normal cleaner not specifically designed to clean glass/windows, we also get the stripes even though we are sure that there are also surfactants in the normal cleaner.

The question is: what is the difference between the glass cleaner and the regular cleaner that makes sure that windows become stripeless clean?

One thought we considered but couldn't really work out was that the stripe formation would be something caused by a combination of the marangoni effect and evaporation, similar to the coffee-stain effect which can be overcome by specific tuning of the surfactants as shown here.

Could someone explain how the stripeless cleaning works? Can fluid dynamics explain what happens or is it really something chemical going on?

[EDIT]

When searching I also ran into a solution that (at least the manufacturers claim) will also give stripeless clean windows. The interesting thing is that they use pure $H_2O$ so without any surfactants but also without any dissolved salts like regular tap water has.

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On the appropriateness of cross-posting: meta.physics.stackexchange.com/a/896/520 . –  dmckee Mar 14 '13 at 0:14
    
Wow what an incredibly awesome question! I wish I could give you more +'s! –  joshphysics Mar 14 '13 at 5:54
3  
I don't know the answer, but I do know that vinegar works as a substitute for window cleaning fluid - maybe that will give a clue to someone? –  Nathaniel Mar 14 '13 at 14:14

2 Answers 2

up vote 3 down vote accepted

This answer was posted on chemistry.SE by @permeakra:

After quick digging I found, that glass cleaner solutions usually contain alcohols and surfactants. This additions reduce surface tension and allows the solution to interact with glass more easily, distributing the solution over the entire surface.

The white stripes visible after water dried are usually solid salts. If the water does not contain any salts, but only compounds, that can quickly evaporate, it will not leave stripes. But it is not addition, but absence of additions that do the trick. For example, most bleacher/toilet cleaners contain hypoclorites, salts of unstalble HOCl acid and leave NaCl after evaporation

When tap water is allowed to dry, it usually leaves white stripes, but they are not visible on most surfaces

The only ideas I can get why the salts don't deposit if using a glass cleaner is that salts are removed (and if you have a cleaner not meant to be diluted, the water in it may be deionized) or to trap salt ions into organic ligands so resulted salts were not crystalline (possible, but I do not like the idea).

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In glass,there can be different types of staining based on how the stains form http://www.britewayservices.com/resources/HardWaterSpots.pdf

Based on your nature of question I think you are talking about limescale staining.Sometimes stains are from due to chemical reaction between silicates and with the calcium and magnesium in hard waters.These minerals deposit on the glass over time and form a type of stain called limescale.One needs some acidic material to remove these type of stains.It breaks the limescale into mild mannered acid.In here http://www.wikihow.com/Remove-Hard-Water-Stains-From-Glass you would find the reasons of using acidic substance including vinegar.

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