(Now thinking about having a day in Calculus class where you force students to punch a block of cornstarch water, and then say: "You see! This is what happens when you rely too heavily on the first-order Taylor expansion!!")
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38. QUASICRYSTALS are materials for which the symmetry is inconsistent with a periodic tiling. For example, a five-fold symmetric crystal is not supposed to exist, since it's impossible to tile space with pentagons. Nonetheless, such materials can exist!pic.twitter.com/JMkHp0YDOc
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They just have tiling that is locally regular but has no long-range order, like Penrose tiles. (left: a real microscopy image. right: Penrose tiles)pic.twitter.com/Ijk21Ve6zL
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All the quasicrystals we have found on earth are apparently meteorite fragments. If you ever want to hear an incredible, adventurous science talk, listen to Paul Steinhardt talk about leading an expedition into Kamchatka to find them:https://www.youtube.com/watch?v=srBjBiEGP7U …
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39. Most materials expand in one direction when you compress them in a perpendicular direction. But AUXETICS are materials that either shrink or expand in both directions simultaneously. (In engineering terms, they have a negative "Poisson ratio")pic.twitter.com/taNnh5Txg7
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There are lots of fun engineering examples of auxetics. But they also appear naturally. Here's one, for example ("cristobalite", a variant of quartz):pic.twitter.com/TUtpBkyh1a
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40. OPTICAL METAMATERIALS are human-made materials in which a bunch of small electromagnetic resonators are arranged so that their interactions produce unusual behaviors of light (or EM waves in some band of frequency). For example, you can engineer negative index of refraction!pic.twitter.com/eEVbH6E53V
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Brian Skinner Retweeted Brian Skinner
41. There is a lot of excitement and mystery right now about SAMARIUM HEXABORIDE, which looks simultaneously like an insulator and a quantum metal, in ways that we are still grappling with. See this earlier thread: (https://twitter.com/gravity_levity/status/1179469564423225344 …)
Brian Skinner added,
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I think that I am out of time and energy now, and tired of spamming your timelines. So let's draw this thread to an END. Thank you all for coming along with me. It's been fun, and nothing at all like a systematic list of "the 100 most interesting materials".
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@vgr I didn't get to 100, but this thread has at least 100 tweets in it and I am now reporting for debriefing2 replies 0 retweets 9 likesShow this thread
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Replying to @gravity_levity
Now I want to start my own museum of materials and buy a microscope to look at them with
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