May 182011

I think I first encountered the term “thixotrope” in conjunction with epoxy and the additives you can mix it with. I remember reading about fumed silica, and was amazed that such a product could be created and sold commercially that was so small in particle size. I’ve worked with fumed silica, and indeed it is an amazing substance.

I suspect that other people might conceptualize the property of thixotropy much like I did, and imagine that it’s a property of a material. But if you look at the definition of thixotropy, at least that given by Wikipedia, you notice that it’s a property of “certain gels or fluids.” What got me thinking about this is that a material can become more or less thixotropic depending on its physical state.

I remember sitting at a Mexican restaurant in LA with some of my cousins back in the summer of 1984 and one of my cousins was pouring a carafe of frozen margarita mixture into a glass. He tipped the carafe higher and higher, but the icy mixture still wouldn’t flow. All of a sudden the mixture started flowing catastrophically, at least as far as the glass and table was concerned… One of my other cousins remarked something to the effect that “he wondered if that was going to happen.”

If I understand the concept of thixotropy correctly, then I believe that water is a sort of “auto-thixotrope” in that it’s a material that can become thixotropic depending on its physical state. A fine grained ice slush, like that in a Slurpee or a margarita, exhibits thixotropy. Neither ice nor water by itself is thixotropic, yet a mixture of the two is.

Perhaps I should qualify the last concept, as when I think about it, I suppose that a block of ice would behave differently physically than the same mass of ice broken up into cubes. Perhaps snow is thixotropic, as I think an avalanche might qualify as an example. So now I have to wonder if particle size, particle shape and temperature are factors as well. With water, or more accurately snow or ice, you have further complications conceptualizing this, as you have the molecular lattice structure on the microscopic scale, as well as the “particle” size and shape on the macroscopic scale. The drink in your hand behaves differently as a material depending on the size and shape of the ice “particles” inside. A Slurppe pours differently than Kool-Aid with ice cubes.

So it makes more sense to me how the definition of “thixotrope” is constructed broadly, to encompass “certain gels or fluids” and not strictly as a property of a material. There is a lot more going on than one simple physical property.

I remember a physics class in college where I was introduced to the fact that there was an entire branch of materials science known as “rheology.” At the time I was amazed that an entire branch of science could be devoted to such an esoteric thing as fluid flow. Now it makes more sense, as I can begin see how complex it really is!

 Posted by on 05/18/2011 Opinion, Science

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