Thursday, April 26, 2012

Salting Out a Carbomer Gel

A very common example of a rheologically interesting material are the hand sanitizer gels that are becoming ubiquitous even outside of healthcare settings. I've visited clients that have had tubes in conference rooms, for example. The gels are mostly ethanol (~ 60%), some carbomer (a generic term for lightly crosslinked polyacrylic acid) and some other entities. The ones we have at home have some water, isopropyl alcohol, tocopheryl acetate (an antioxidant based on vitamin E), glycerin, propylene glycol, isopropyl myrisate, and some fragrance.

Carbomers are very effective gelling agents. You only need a few percent to get a nice thick gel and they are reasonably insensitive to pH. But if you've ever worked with them, you very quickly realize their Achilles Heel: salt. Salt will very quickly collapse a gel, so you usually either need to work with purified water or you add more carbomer to compensate, an expensive proposition as they are not cheap.

Salting out a gel is so easy that even a dumb, drunk teenager could do that, and that is exactly what is happening. Teenagers are salting out hand sanitizer gels in order to make them more drinkable. Drinkable? That's probably not the right word. I certainly wouldn't consider salty, denatured ethanol to be drinkable. But in this case, by drinkable I mean less viscous and more fluidic.

Being 120 proof, the liquid will certainly pack quite a punch, and kids are starting to show up at emergency rooms rather ill (probably from all the adulterants more than the ethanol itself). But as one columnist observed, this all goes to show that "Hand Sanitizer Chugging Proves American Teens may the World's Stupidest".


Chemjobber said...

Glad to see I made the right guess:

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