1 00:00:07,207 --> 00:00:08,540 JESSICA HARROP: Hi, I'm Jessica. 2 00:00:08,540 --> 00:00:10,956 And I'm going to be talking about a chemical demonstration 3 00:00:10,956 --> 00:00:14,670 today that I like to call let it snow. 4 00:00:14,670 --> 00:00:17,210 MIT's Dr. John Dolhun-- 5 00:00:17,210 --> 00:00:19,460 here he is-- and his assistant, Arielle, 6 00:00:19,460 --> 00:00:22,220 are going to perform two magic tricks involving 7 00:00:22,220 --> 00:00:24,260 super absorbent polymers. 8 00:00:24,260 --> 00:00:26,960 Let's watch as they show us the first one at the Cambridge 9 00:00:26,960 --> 00:00:28,500 Science Festival. 10 00:00:28,500 --> 00:00:29,000 [WHOOSH] 11 00:00:29,000 --> 00:00:29,930 JOHN DOLHUN: And what I'm going to do 12 00:00:29,930 --> 00:00:32,299 is I'm going to pour some water into the beaker 13 00:00:32,299 --> 00:00:34,400 that she's holding. 14 00:00:34,400 --> 00:00:37,880 And you keep your eyes on the beaker. 15 00:00:37,880 --> 00:00:40,220 Bring it down just a bit. 16 00:00:40,220 --> 00:00:40,850 Hold it firmly. 17 00:00:47,700 --> 00:00:54,200 Turn it to-- we are making snow. 18 00:00:54,200 --> 00:00:56,015 We're making snow today, Arielle. 19 00:00:56,015 --> 00:00:56,985 ARIELLE LUBIN: Oh, boy. 20 00:00:59,900 --> 00:01:01,070 It's so cold and wet. 21 00:01:01,070 --> 00:01:02,237 It's just like real snow. 22 00:01:02,237 --> 00:01:02,736 Look! 23 00:01:05,431 --> 00:01:05,930 [WHOOSH] 24 00:01:05,930 --> 00:01:07,304 JESSICA HARROP: So what happened? 25 00:01:07,304 --> 00:01:08,990 Well, Arielle was holding a beaker 26 00:01:08,990 --> 00:01:11,780 containing some sodium polyacrylate, which 27 00:01:11,780 --> 00:01:13,820 is a polymer. 28 00:01:13,820 --> 00:01:15,560 Now a polymer is a big molecule that's 29 00:01:15,560 --> 00:01:19,350 a chain of repeating units. 30 00:01:19,350 --> 00:01:20,210 This is the unit. 31 00:01:25,036 --> 00:01:26,785 And this is what it looks like in a chain. 32 00:01:40,910 --> 00:01:45,700 Now, different chains are held together by cross links. 33 00:01:45,700 --> 00:01:47,780 The et cetera just means that this could 34 00:01:47,780 --> 00:01:49,760 be thousands of carbons long. 35 00:01:49,760 --> 00:01:53,880 This is just a small part of the chain and the polymer. 36 00:01:53,880 --> 00:01:55,940 Now when water is added to the polymer, 37 00:01:55,940 --> 00:01:58,280 it wants to rush into the material because 38 00:01:58,280 --> 00:02:02,365 of the presence of so many sodium and carboxylate ions. 39 00:02:26,950 --> 00:02:30,640 The water displaces the sodium ions leaving negatively 40 00:02:30,640 --> 00:02:32,980 charged carboxylic ions. 41 00:02:32,980 --> 00:02:35,230 These repel each other and the repulsion 42 00:02:35,230 --> 00:02:38,050 causes the polymer, which starts out wound together, 43 00:02:38,050 --> 00:02:41,350 to unwind, swell, and stretch. 44 00:02:41,350 --> 00:02:44,680 The cross lengths, which connect the polymer chains together, 45 00:02:44,680 --> 00:02:47,890 prevent them from breaking apart in the water. 46 00:02:47,890 --> 00:02:50,530 And the fake snow that's created is the same snow 47 00:02:50,530 --> 00:02:53,110 they use in Hollywood movie sets. 48 00:02:53,110 --> 00:02:56,650 Now, let's watch Dr. Dolhun and Arielle turn this same polymer 49 00:02:56,650 --> 00:02:58,570 into something totally different. 50 00:02:58,570 --> 00:03:00,250 [WHOOSH] 51 00:03:00,250 --> 00:03:03,250 JOHN DOLHUN: OK, so I've got another beaker she's holding. 52 00:03:03,250 --> 00:03:07,075 And I'm going to pour some water in it and observe. 53 00:03:17,310 --> 00:03:18,490 Turn it over, Arielle. 54 00:03:21,300 --> 00:03:23,300 You don't have to hold your hand under the hole. 55 00:03:26,740 --> 00:03:28,630 That's the same polymer. 56 00:03:28,630 --> 00:03:31,090 Only this time the polymer is not 57 00:03:31,090 --> 00:03:33,760 as cross-linked as the first one. 58 00:03:33,760 --> 00:03:36,500 It's more of the straight chain polymer. 59 00:03:36,500 --> 00:03:41,800 And it can absorb many more times its weight in water. 60 00:03:41,800 --> 00:03:43,120 You'll recognize this. 61 00:03:43,120 --> 00:03:46,020 This is the diaper polymer. 62 00:03:46,020 --> 00:03:48,380 You know now, right? 63 00:03:48,380 --> 00:03:48,880 [WHOOSH] 64 00:03:48,880 --> 00:03:51,550 JESSICA HARROP: So Dr. Dolhun uses the same polymer 65 00:03:51,550 --> 00:03:54,040 with a different amount of cross linking. 66 00:03:54,040 --> 00:03:56,440 The sodium polyacrylate that makes diaper gel 67 00:03:56,440 --> 00:03:58,750 has fewer cross-links and therefore can 68 00:03:58,750 --> 00:04:01,600 absorb more water than the sodium polyacrylate that 69 00:04:01,600 --> 00:04:03,890 turned into snow. 70 00:04:03,890 --> 00:04:06,820 Overall, this polymer can absorb up to 800 times 71 00:04:06,820 --> 00:04:09,760 its own weight in distilled water and about 30 72 00:04:09,760 --> 00:04:12,050 times its own weight in urine. 73 00:04:12,050 --> 00:04:13,900 It's the main ingredient in baby diapers 74 00:04:13,900 --> 00:04:15,345 used to keep the baby dry. 75 00:04:15,345 --> 00:04:15,970 [MUSIC PLAYING] 76 00:04:15,970 --> 00:04:19,290 Hope you enjoyed the video and I'll see you next time.