This was originally posted on Sustainable Nano, which is my new project. You should go check it out! Science Minus Details will live on though! Poop posts will come, have faith!!!!
As with all good meals of information, let's start this one off with ice cream!
In an effort to grow out of my "slim fit" clothes, I've begun an ice-cream-after-every-dinner diet.
In order to understand this gritty phenomenon, let's talk first about what gives freshly purchased ice cream that wonderfully non-gritty texture. The ice cream manufacturing process is controlled very carefully, such that the ice in ice cream comes in the form of lots of super-tiny ice crystals. These ice crystals are usually around 10 to 100 micrometers in size, which is so small that our tongues can't even detect them as crystals, which is one reason ice cream is so smooth! However, if their size increases significantly, our tongue noticed the crystals and the ice cream tastes gritty. But how do the crystals get bigger? Well, as we talked about in the previous post, small crystals have more surface area compared to an equal mass of large crystals. This means that lots of the atoms that make up small crystals are stuck out on the surface of those crystals, instead of being nestled on the inside. Those surface atoms would much rather be on the inside of the crystal, surrounded by other identical atoms. We scientists would say the surfaces of crystals have extra energy, relative to the insides of crystals.
|Water molecules on the surface of ice crystals have extra "surface energy" because they aren't fully surrounded by other water molecules.|
An even cooler way crystals can grow larger is by stealing individual unhappy surface atoms from other crystals. Basically, the surface atoms are so unhappy, they simply "abandon ship" and wash up on the shores of another crystal, making that second crystal larger. This process results in larger crystals growing and smaller crystals shrinking. This can continue to happen until the small crystals disappear completely! Cool!
|Ostwald ripening. Surface molecules move from one crystal to another. This results in the growth of larger crystals because they have less surface area per unit volume.|
|Gold nanoparticles can act as "catalysts" in chemical reactions.|
References & Further Reading (subscription/purchase required for some):
Clark, C. The Science of Ice Cream; Royal Society of Chemistry: Cambridge, 2004.
Halford, B. Ice Cream. Chem. Eng. News, 2004, 82, 51.
Corma, A.; Garcia, H. Supported gold nanoparticles as catalysts for organic reactions. Chem. Soc. Rev., 2008, 37, 2096.
An, K.; Somorjai, G. A. Size and Shape Control of Metal Nanoparticles for Reaction Selectivity in Catalysis. ChemCatChem, 2012, 4, 1512.
Zhong, C.J; Luo, J.; Fang, B.; Wanjala, B. N.; Njoki, P. N. Loukrakpam, R.; Yin, J. Nanostructured catalysts in fuel cells. Nanotechnology, 2010, 21, 1.
Mudunkotuwa, I. A. and Grassian, V. H. The Devil is in the Details (or the Surface): Impact of Surface Structure and Surface Energetics on Understanding the Behavior of Nanomaterials in the Environment. J. Environ. Monit. 2011, 13, 1135.