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Hi, I'm Jessica
嗨，我是Jessica
and I'm gonna be talking about a chemical demonstration today that
今天我要讲的化学演示
I like to call let it snow
叫作"下雪"
MIT's Dr. John Dolhun
MIT的John Dolhun博士
here he is
这就是他了
and his assistant Arielle are going to perform 2 magic tricks
他和助手Arielle将演示两个神奇的实验
involving superabsorbent polymers
用到高吸水性聚合物
Let's watch as they show us the first one at the Cambridge Science Festival
首先来看剑桥科学节上他们所演示的第一个实验
What I'm going to do is I'm going to pour some water
我将倒一些水
into the beaker that she's holding
到她所拿的烧杯
and you keep your eyes on the beaker
你们看好烧杯里的情况
Bring it down just a bit
往下拿一点
Hold it for me
拿好了
Turn it to them
拿给观众看
We are making snow
我们在造雪
We're making snow today, Arielle
我们正在造雪 Arielle
Oh boy
乖乖
It's so cold and wet. It's just like real snow
它又冷又湿，就像真雪一样
Look
看
So what happened?
发生了什么呢
Well, Arielle was holding a beaker containing some sodium polyacrylate
Arielle所拿的烧杯中装有聚丙烯酸钠
which is a polymer
这是一种聚合物
Now a polymer is a big molecule that's a chain of repeating units
聚合物是一条由重复单元组成的长链分子
This is the unit
这是重复单元
And this is what it looks like in a chain
这是它们组成链的情况
Now different chains are held together by crosslinks
不同的链由交联连在一起
The etc just means that this could be thousands of carbons long etc
(等等)表示这里可以有数千个碳那么长
This is just a small part of the chain in the polymer
这只是聚合物链中的很小一部分
Now when water is added to the polymer
当水被加入到聚合物中时
it wants to rush into the material
水会希望涌入到物质中
because of the presence of so many sodium and carboxylate ions
因为这里有很多钠离子和羧酸根离子
The water displaces the sodium ions
水会结合并移走钠离子
leaving negatively charged carboxylate ions
剩下带负电荷的羧酸根离子
