Leaf boat powered by pen juice — Transcript

Full transcript

1. 0:00- If you blow the ink out of a ballpoint pen onto a leaf
2. 0:02and then put it on water, this happens.
3. 0:05It's cool, isn't it?
4. 0:07I saw a few posts on Reddit,
5. 0:08and I thought it'd be cool to find out what's going on.
6. 0:12I originally thought it would be a good idea
7. 0:13to do the experiment on milk
8. 0:15because then the ink would stand out better.
9. 0:18And I thought, actually,
10. 0:19that could get gross really quickly.
11. 0:21So this is actually titanium dioxide
12. 0:24swirling around in water, and it works really well
13. 0:26with the ink from a red ballpoint pen.
14. 0:31For comparison, this is black ballpoint pen ink.
15. 0:36What's really cool though about this layer of ink
16. 0:39ejected from the back of the leaf is that it's really shiny.
17. 0:42So by using a black container instead
18. 0:46and making sure that the white ceiling in my studio
19. 0:49is well illuminated, the shiny ink trail really stands out.
20. 0:55The floating patches of ink left behind
21. 0:57are really interesting, like they're quite brittle.
22. 1:00If I move my finger up through the ink,
23. 1:03you can see it breaks into lots of little shards.
24. 1:06It doesn't only work with leaves, of course.
25. 1:08Here's a piece of paper being propelled around by ink,
26. 1:12and here's a droplet of ink spreading round on its own.
27. 1:15All the ink I've shown you so far
28. 1:17is from Biro branded pens.
29. 1:19I also bought some Tesco branded pens,
30. 1:22and here's a side-by-side comparison
31. 1:24of the different colors.
32. 1:25It's interesting to see how the shapes vary between the two,
33. 1:29presumably because the chemistry is a little bit different.
34. 1:32This is really reminiscent of at least two phenomena
35. 1:34that I've seen before,
36. 1:35but I think the mechanism is different to those two.
37. 1:38In this case, the first thing you might think of
38. 1:41is dish soap powered propulsion.
39. 1:44Look here, this boat is propelled forward
40. 1:47when you add a drop of dish soap to the cavity,
41. 1:50this happens because the dish soap
42. 1:52reduces the surface tension of water.
43. 1:54So you have low surface tension here
44. 1:56and high surface tension here.
45. 1:58It's a bit like popping a balloon.
46. 2:00This high tension area recedes under that tension.
47. 2:03And so the area of low surface tension expands.
48. 2:07The boat is at the edge of that region
49. 2:09and so is carried away as it grows,
50. 2:13but I don't think that's what's happening with the ink.
51. 2:16You may also remember the spinning glue video that I made.
52. 2:19I'm not 100% sure what powers the spinning glue,
53. 2:22but what I think I worked out during that video
54. 2:25is that solvent is ejected from the blob into the water.
55. 2:30And that's what powers the movement of the blobs.
56. 2:33Again, I don't think that's what's happening with the ink.
57. 2:36To try and figure it out,
58. 2:37it's worth looking at the chemistry of a ballpoint pen.
59. 2:40Well, the pigment in an ink actually starts off as a powder
60. 2:43like carbon black for blank or this oisine for red,
61. 2:48for the dye to be able to flow onto a page,
62. 2:51it needs to be dissolved in a solvent.
63. 2:54In the case of a felt tip pen, that might be an alcohol.
64. 2:58And when a felt tip pen mark dries on the page,
65. 3:02it's because the alcohol is evaporating
66. 3:05leaving the dye behind,
67. 3:07but ballpoint pen ink is much thicker than felt tip pen.
68. 3:11That's because the dye in a ballpoint pen
69. 3:13is dissolved in an oily solvent, like phenoxy ethanol.
70. 3:20Do you know what?
71. 3:23It smells just like a ballpoint pen.
72. 3:25You know that, it's like a perfume you smell.
73. 3:29I mean, it's obvious, I suppose, but that's cool.
74. 3:33Phenoxy ethanol doesn't evaporate
75. 3:35like the solvent in a felt tip pen,
76. 3:37or at least not in a timely manner.
77. 3:38Instead of when a ballpoint pen stroke is drying
78. 3:41it's because the phenoxy alcohol is bonding
79. 3:45to the fibers of the page and also oxidizing in the air.
80. 3:49That's all very interesting, but from our point of view,
81. 3:51we want to know how it behaves on water.
82. 3:53When a drop of phenoxy ethanol first hits the water,
83. 3:56it spreads out, and then over a few seconds it disappears.
84. 3:59I believe that's because it's dissolving into the water.
85. 4:03Phenoxy ethanol isn't very soluble in water.
86. 4:06And in fact, if you keep adding it,
87. 4:08eventually droplets will sink to the bottom
88. 4:10instead of dissolving.
89. 4:12By dropping phenoxy ethanol onto water
90. 4:14that already had a crusty layer of ink on it,
91. 4:17I managed to capture this really interesting behavior.
92. 4:21Isn't that cool?
93. 4:22And I honestly have no idea why it's doing that.
94. 4:26The spreading out bit is important.
95. 4:28Presumably if there was dye
96. 4:30dissolved in the phenoxy ethanol,
97. 4:33that dye would be carried with it as it spread out.
98. 4:36Why would one liquid spread out so quickly
99. 4:39on the surface of another liquid?
100. 4:41Well, I think it comes down to
101. 4:42how well the molecules in the liquid bond to each other
102. 4:46versus how well they bond to water.
103. 4:48Like if a molecule of phenoxy ethanol
104. 4:51bonds more energetically to a molecule of water
105. 4:54than to another molecule of phenoxy ethanol,
106. 4:57then it will spread out across the water to minimize energy.
107. 5:01Here's some phenoxy ethanol with the dye dissolved in it.
108. 5:05And yes, as it spreads out,
109. 5:07it carries some of the dye with it,
110. 5:09but it certainly doesn't look the same
111. 5:11as when we use regular pen ink.
112. 5:14Like the ink isn't forming a crust,
113. 5:17it's just swirling around there dissolving into the water.
114. 5:20So there must be something else going on.
115. 5:22Another candidate is a oleic acid which is an ingredient
116. 5:26used as a lubricant in ballpoint pens.
117. 5:29I actually used a oleic acid in a video
118. 5:31on Matt Parker's channel to calculate Pi for Half Tau Day.
119. 5:35The reason you can use a oleic acid to calculate Pi
120. 5:38is because it will spread out into a circle,
121. 5:42one molecule thick on the surface of water
122. 5:45if you do it right, and using Avogadro's number,
123. 5:48you can work backwards and calculate Pi.
124. 5:50Yes, it's a ridiculous idea.
125. 5:53What's interesting though,
126. 5:54is if I just drop a blob over oleic acid on water,
127. 5:58it doesn't spread out into one molecule thick layer.
128. 6:01It bunches up like this.
129. 6:04I suspect that it's because in the Avogadro's number video
130. 6:08on Matt's channel, I was using a solvent,
131. 6:10and the concentration of a oleic acid
132. 6:12was really, really low,
133. 6:14but I don't fully understand that behavior.
134. 6:17But anyway, I don't think oleic acid is the thing
135. 6:20working to spread the encounter in this case.
136. 6:24Another possible candidate is a surfactant.
137. 6:27Surfactants are added to ballpoint pen inks
138. 6:30to help them bind to the paper,
139. 6:33and just like dish soap,
140. 6:34a surfactant lowers the surface tension of water.
141. 6:38So it might actually be that we have something similar
142. 6:41to that dish soap propulsion, but I'm not convinced.
143. 6:46Like if it was a surfactant lowering the surface tension,
144. 6:50then surely these ink rafts would be constantly breaking up
145. 6:56and crumbling and spreading out
146. 6:58as the surface tension was being pulled outwards.
147. 7:02Actually the obvious test to do
148. 7:03is to put the phenoxy ethanol on the tip of a leaf
149. 7:06on its own and see what happens.
150. 7:10Well, to me, that's pretty good evidence that the process
151. 7:13is at least partially driven by phenoxy ethanol.
152. 7:17But the particular way that the ink trail forms
153. 7:21is a bit harder to pin down.
154. 7:23I suspect that in combination
155. 7:25with some of the other ingredients,
156. 7:27it behaves in just the right way
157. 7:29so that it carries the right amount of ink with it.
158. 7:33The layer becomes thin fast enough,
159. 7:35and it dissolves into the water fast enough
160. 7:38that you just get this perfect raft of ink.
161. 7:41It's weird that the dye doesn't dissolve in the water
162. 7:44like it did when we were using phenoxy ethanol
163. 7:46on its own with the dye.
164. 7:48Perhaps one of the other ingredients acts as a barrier
165. 7:51between the diet and the water.
166. 7:53Maybe the oil or something reacts with the water
167. 7:56and becomes a hard surface that traps the dye.
168. 8:00I have played around
169. 8:02with different combinations of ingredients.
170. 8:03For example, here is the dye
171. 8:05with phenoxy ethanol and oleic acid.
172. 8:10And here's the dye mixed with phenoxy ethanol,
173. 8:13oleic acid and a surfactant.
174. 8:16I tried these different ingredients
175. 8:18in different concentrations.
176. 8:19I didn't get anything much different
177. 8:22than what I've shown you already.
178. 8:23So there's still a mystery here.
179. 8:26You know, it's been fun finding out
180. 8:27about the chemistry of ballpoint pens.
181. 8:29And I feel like we're closer
182. 8:30to a description of what's going on.
183. 8:32If you have any insights, let me know in the comments.
184. 8:35There'll also be a discussion happening
185. 8:37on the Steve Mould's sub-Reddit.
186. 8:38I'll leave a link to that in the description as well.
187. 8:40One of the best things about this job is that I get to work
188. 8:43through mysteries for myself until I understand them.
189. 8:47Like there's not that much information online
190. 8:49about how a ballpoint pen works,
191. 8:51but I was able to find the ingredients,
192. 8:54order them online and play with them,
193. 8:56see how they behave and work it out.
194. 8:58And they say that the best way to learn
195. 9:01is by doing it for yourself.
196. 9:04The sponsor of this video, Brilliant,
197. 9:06have taken that concept
198. 9:08and turned it into an interactive STEM learning platform.
199. 9:13I've worked with and used Brilliant for years.
200. 9:16And it's been really interesting to see
201. 9:18how the interactivity of the platform has increased.
202. 9:22Recently, there's been a big push,
203. 9:24and there's loads of interactive stuff.
204. 9:25Look at this lesson on derivatives.
205. 9:28I was actually really lucky at school
206. 9:30to be taught derivatives and other calculus ideas
207. 9:33in this really visual interactive way.
208. 9:36And it's really heartening
209. 9:38to see Brilliant doing the same thing online.
210. 9:42Brilliant also has courses on things
211. 9:43like geometry, scientific thinking,
212. 9:47even things like quantum computing, cryptocurrency.
213. 9:51There's an app, as well as a desktop site.
214. 9:54And honestly, that's the main way that I use Brilliant.
215. 9:57It's something I do before bed, just 'cause it's really fun.
216. 10:00If you're interested in trying out Brilliant,
217. 10:02you should use my special URL, brilliant.org/stevemould.
218. 10:06That gives you 20% off a full year
219. 10:09of STEM learning with Brilliant.
220. 10:11The link is also in the description.
221. 10:12So checkout Brilliant today.
222. 10:14Hope you enjoyed this video.
223. 10:15If you did, don't forget to hit subscribe,
224. 10:17and the algorithm thinks you'll enjoy this video next.
225. 10:21(upbeat jazzy music)