1 00:00:00,500 --> 00:00:01,835 [SQUEAKING] 2 00:00:02,335 --> 00:00:04,170 [RUSTLING] 3 00:00:04,670 --> 00:00:05,915 [CLICKING] 4 00:00:05,915 --> 00:00:07,790 CAROLYN JONS: This is Goodie Bag number nine. 5 00:00:07,790 --> 00:00:09,590 In today's video, we will be exploring 6 00:00:09,590 --> 00:00:12,170 the topics of polymerization and cross-linking 7 00:00:12,170 --> 00:00:13,790 and learning how these processes can 8 00:00:13,790 --> 00:00:16,190 be used to make slime at home. 9 00:00:16,190 --> 00:00:19,430 You'll need gloves, Elmer's glue, borax powder, 10 00:00:19,430 --> 00:00:22,520 plastic cups, and spoons for stirring. 11 00:00:22,520 --> 00:00:24,740 One product made of polymers that many people are 12 00:00:24,740 --> 00:00:26,600 familiar with is Silly Putty. 13 00:00:26,600 --> 00:00:30,330 Silly Putty is made of a polymer called polydimethylsiloxane. 14 00:00:30,330 --> 00:00:32,630 Polydimethylsiloxane is made of repeating 15 00:00:32,630 --> 00:00:35,840 units called monomers that include a silicon, an oxygen, 16 00:00:35,840 --> 00:00:38,720 and two CH3 groups. 17 00:00:38,720 --> 00:00:41,120 Today we're going to make an alternative material that 18 00:00:41,120 --> 00:00:42,860 behaves a little bit like Silly Putty, 19 00:00:42,860 --> 00:00:45,350 but is instead made of a different polymer. 20 00:00:45,350 --> 00:00:48,020 This can be made by combining Elmer's glue 21 00:00:48,020 --> 00:00:49,535 and cross-linking with borax. 22 00:01:03,540 --> 00:01:06,660 As you can see, after I added borax to the Elmer's glue, 23 00:01:06,660 --> 00:01:08,820 the material became much more viscous. 24 00:01:08,820 --> 00:01:10,680 This is because of cross-linking. 25 00:01:10,680 --> 00:01:13,410 Cross-linking is forming a bond to link one polymer 26 00:01:13,410 --> 00:01:14,600 chain to another. 27 00:01:14,600 --> 00:01:16,830 In this experiment, the polyvinyl alcohol 28 00:01:16,830 --> 00:01:20,730 and Elmer's glue forms hydrogen bonds with the boric acid. 29 00:01:20,730 --> 00:01:23,220 These cross-links make it more difficult for the polymer 30 00:01:23,220 --> 00:01:24,865 chains to slide past one another, 31 00:01:24,865 --> 00:01:27,360 so the material becomes more viscous. 32 00:01:27,360 --> 00:01:29,700 By adding in more borax, we increase the number 33 00:01:29,700 --> 00:01:31,800 of cross-links, and this results in a material 34 00:01:31,800 --> 00:01:34,360 more resistant to flow. 35 00:01:34,360 --> 00:01:36,370 You may have noticed that when we pull quickly, 36 00:01:36,370 --> 00:01:37,600 the slime breaks in half. 37 00:01:37,600 --> 00:01:40,450 But when we pull slowly, the slime is able to stretch. 38 00:01:40,450 --> 00:01:43,660 This is because the slow pulling allows hydrogen bonds to break 39 00:01:43,660 --> 00:01:46,480 and then reform, allowing the chains to more easily slide 40 00:01:46,480 --> 00:01:48,880 past one another. 41 00:01:48,880 --> 00:01:51,250 In this Goodie Bag, we hope you had an opportunity 42 00:01:51,250 --> 00:01:54,220 to make a polymer of your own and witness how cross-linking 43 00:01:54,220 --> 00:01:57,270 can change material properties.