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前言

兔子是毛茸茸的, 烂泥是黏糊糊的, 气球是有弹性的. 那么什么物质即毛茸茸又黏糊糊又有弹性,而且还很好玩呢? 这就是弹性橡皮泥(Silly Putty), 加克(Gak)和粘液!

另外这些物质还让我们困惑。因为大部分这些物质在低温时会变硬,而随着自身温度的升高变得更易流动。我们可以回忆一下,天冷的时候,蜂蜜是从瓶口缓慢地流出来的,而天气炎热的时候,它就会快速地从瓶子里冒出来。弹性橡皮泥(Silly Putty), 加克(Gak)和粘液是不一样的。当你把它们紧握在拳头里时你会感觉到它们像固体一样坚硬,但是一旦你松开拳头,它们就会像浓稠的液体一样从你的手指间滑下。为什么粘液会不一样?在这个实验活动中,你将会制作你自己的粘液,还可以玩一玩,从中还能发现是什么让粘液流动了!

第 1 段(可获 1.74 积分)

背景

粘液到底是固体还是液体呢?固体是由紧紧地固定地挨在一起的颗粒组成,因此有固定的形状。这些颗粒被称为分子或者原子。液体也有这种颗粒,这些颗粒可以自由滑动,液体也就可以自由流动。加热可以使某些液体,比如水或者油更易流动,反之亦然,这些液体被称为牛顿液体。非牛顿液体,比如番茄酱和粘液,却不太一样。像挤压、搅拌这些动作也可以使他们流动起来。有时他们又会变得非常粘稠—或者说不易流动—以致于被错当成固体。

第 2 段(可获 1.39 积分)

无色学生胶可以被当做非牛顿液体的一种,这种胶本身是一种聚合物。聚合物是由一些长链的单体组成。一种聚合物可能由数十万种单体组成。聚合物也被称为高分子或者大型分子。聚合物有人工合成的,比如塑料和尼龙。也有天然的,比如DNA、小麦谷蛋白和淀粉。

无色学生胶是一种液体,因为它的长聚合物可以滑动。然而它不易流动,它有很强的粘性。添加某些化学物质—比如硼砂溶液(或者四硼酸钠水溶液)—能使聚合物间交联.这就好像很长的分子间牵起了手.这些聚合物彼此间可以相互滑动,这时这种胶仍旧是液体还是变成了固体?

第 3 段(可获 1.85 积分)

材料

  • 容器
  • 埃尔默的胶水或者其他聚醋酸乙烯酯(PVA)类的胶水
  • 热水
  • 搅拌棒或塑料勺
  • 硼砂
  • 量匙(1/2汤匙)
  • 量杯(1/2和1/4杯)
  • 护目镜或其他眼睛保护装置(处理硼砂会刺激眼睛)
  • 已做过防护处理的工作空间(和工作服) ,这样粘液粘在上面时不会被损坏
  • 成年助手
  • 食用色素或标记(可选)
  • 自封袋或密封容器,用于存储粘液(可选)

准备工作

  • 对工作空间和衣服做好防护处理—粘液很粘,很难去除!
  • 戴上护目镜或眼镜,因为硼砂溶液会刺激眼睛。
  • 请成年助手把1/2汤匙的硼砂粉搅拌到半杯温水中。搅拌至溶液清澈为止,将容器标记上“2%硼砂溶液”备用。
第 4 段(可获 1.8 积分)

Procedure

  • Pour one half cup of glue and one quarter cup of warm water in a container. Note that this solution has 2/3 (or 67 percent) glue.
  • Optional: If you like colored slime, you can mix in a few drops of food coloring. Another option is to put the tip of a marker into the water for a short time so the ink dissolves in the water.
  • Stir the glue/water mixture with the stirring rod.
  • Add five tablespoons of the borax solution to your glue/water mix.
  • Stir with the stirring rod. After some stirring, you should see a substance sticking to your stirrer. Does the sticky substance look like a solid or like a liquid—or can you not tell yet?
  • If your substance is still watery, add more borax solution ¼ tablespoon at a time until there is very little watery solution left.
  • Collect the sticky substance in your hands and work it with your hands for about one minute. How does the slime feel? How does the stickiness and stretchiness change when you work it for a while?
  • Would you say the slime is a liquid, or is it more like a solid?
  • Squeeze your slime into an oval and use both hands to pull it apart quickly. Does it tear or elongate?
  • Squeeze your slime into an oval again and use both hands to pull it apart slowly. Does it tear or elongate? How thin can you get it?
  • Work your slime with your hands to form a ball. Try to stick your finger into it forcefully. How deep does your finger go?Does it feel like you poked your finger into something solid, or something liquid?
  • Now try to stick your finger into it gently. How deep does your finger go?Does it feel like you poked your finger into something solid, or something liquid?
  • Squeeze your slime into a ball again and put it in a container. What do you think will happen if you leave it there for a while? Will it stay in an oval, like a solid would do, or will it relax into a puddle and take the form of the container, like a liquid would do?
  • Optional: To keep your slime nice and soft, store it in an airtight container or ziplock bag.
第 5 段(可获 4.81 积分)
  • Extra: Add other substances, such as shaving cream or liquid soap, to your glue/water solution. Will you still obtain slime? How will this slime feel and look different?
  • Extra: Leave your slime uncovered for a day. What do you think will happen? Will it become more like a solid, or start to flow easier? Why do you think this will happen?

Observations and results

Did the slime sometimes feel like a solid and sometimes like a fluid? This is expected.

This type of slime thickens or becomes harder or more viscous when you squeeze or stir it. This happens because it is made up of very long particles that are cross-linked. When you leave the particles alone they will coil up, and the coils can slide over each other. When you apply pressure by squeezing or stirring, some coils unwind and become entangled, making it harder for the slime to flow.

第 6 段(可获 1.9 积分)

When you stirred your slime, tried to rip it apart or poked your finger into it with force, the polymers were entangled and it looked like a solid. As a result, it was hard to stir, it ripped apart, and your finger bounced back.

When you left your slime alone to rest, gently pulled it apart or gently poked your finger in it, the polymers were curled up. They could slide over one another, and it felt more like a liquid. As a result, the slime took the form of the container, it could be stretched thin, and your finger could move through it. It did not flow as easily as water because it consists of long cross-linked particles, whereas water consists of small particles. When a substance keeps its volume but loses its form when left alone, scientists call it a liquid.

第 7 段(可获 1.79 积分)

Cleanup

Do not pour glue solutions or slime down a drain because they can form clogs. Instead, throw them away in the garbage. Wash all equipment with soapy water.

第 8 段(可获 0.36 积分)

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