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Name: Davin Status: educator Grade: 4-5 Location: MD Country: USA Date: Winter 2011-2012

Question:
My fifth grade students and I are learning about evaporation, absorption and residue. We are using two brands of sanitation wipes. Will either of these products leave behind a residue (invisible) after drying? Product One includes: Alkyl (50% C14, 40% C12, 10% C16) dimethyl benzyl ammonium chlorides and Ethanol Product Two includes: Substrate, Isopropyl alcohol, Alkyl dimethyl benzyl ammonium chloride, Alkyl dimethyl benzyl ethylbenzyl ammonium chloride, Alkyl polyglucoside, Preservative and Propylene glycol propyl ether

Replies:
Hi Davin - I am pretty sure both wipes will leave behind some residue.

In order to leave no residue, all components must be volatile. The wipe leaves behind a film of water with components dissolved in it. The water evaporates, then if the others substances evaporate too, at the end there will be no residue.

Product One: C14 alone would be a slow-evaporating oil; add benzyl and a salt to the molecule and it is probably a stable solid. I am not sure it will crystallize much.

Product Two: The Alkyl polyglucoside will definitely be a persistent residue. The "preservatives" usually have multiple carbon rings, so the molecules attract each other well enough to be solid and sublime slowly at high temperatures or never. (Napthalene (2-rings) sublines, anthracene (3-rings) never does.) They will evaporate very slowly if at all. Compiled as a solid they would be somewhere between aspirin powder and crusty old bakelite plastic. The alkyl-benzyl ammonium chlorides I have not looked up yet, but they are each probably about like the solute in Product One. The Alkyl could be small like C3 or C6, or big like C14; the word Alkyl is ambiguous.

So I think both will leave behind an invisible film. Product One has a chance of going away after a day in a warm ventilated oven. Both would probably be mostly removed by rinsing off with pure water or an alcohol/water mix, especially if done before they dry the first time. Product Two's residue has a chance of resisting a brief pure-water rinse, if it is well dried first.

It sounds like you are planning to make the invisible residues somehow visible, which would be a cool thing to do. I'd be curious to hear you methods...

Jim Swenson


Both products contain dimethyl benzyl ammonium chlorides. Neither will evaporate under “normal” conditions. Both will leave some residue. Whether the residue is visible or not depends upon how much is present. In use the film is often rubbed. This may reduce the amount of residue to a point that the residue is not easily visible with the naked eye.

Vince Calder


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