Some are attracted to each other and merge,

一些會相互吸引然後結合

while others repel and chase each other.

而有些則會排斥與追逐彼此

It looks just like the tiny world of micro-organisms, but why?

看起來就像個微生物世界，為何會這樣？

Well if you want to try this out for yourself

如果你想自己試試

You need to get some ordinary food coloring and dilute it with distilled water using a pipette.

你要有一般的食用色素，以滴管加入蒸餾水稀釋

Then pass the microscope slide through a flame for about thirty seconds.

接著用火焰烘烤顯微鏡載玻片約 30 秒

Let it cool, and then put some drops of different concentration on to the slide.

待冷卻後，在玻片上滴幾滴不同溶液

You'll find that drops of similar concentration attract each other and merge

你會發現濃度相似的溶液水滴相互吸引並結合

while drops of different concentrations chase each other.

而濃度不同溶液水滴則會相互追逐

You can draw guides on the slide using permanent marker, which is hydrophobic

你還能拿疏水性的麥克筆畫出引道

and set up long distance pursuits.

讓水滴沿著追趕

Or you can find that drops of similar concentration attract each other

或者看著相似溶液的水滴仍然互相吸引

despite the hydrophobic barriers.

即使有著疏水性的屏障

But how is this possible just using ordinary food coloring and water?

不過只是水跟食用色素為什麼會有這麼奇妙的現象?

Well the key is evaporation.

關鍵就在蒸發

Each drop is constantly evaporating, so around it is an envelope of vapour.

每個水滴都不斷地在蒸發，所以會被一層水氣包覆

The rate of evaporation depends on the humidity around the drop

蒸發的快慢取決於周遭的濕度

so the drier the air is, the faster the rate of evaporation.

周圍的空氣越乾燥，水滴蒸發的越快

So when any two drops are close enough

所以當兩個水滴很靠近彼此

the humidity between them is greater than than the humidity around them,

兩者中間地帶的溼度就會大於外圍

and therefore there's more evaporation around the droplets

所以外圍會蒸發的比較快

then in-between them,

中間蒸發的較慢

and this pushes them together.

兩者之間的壓力差便把他們推向對方

So differential evaporation makes the droplets attract,

所以蒸發速率差會讓水滴互相吸引

but that's not the whole story.

不過還不只如此

Food coloring is a mixture of mainly two molecules,

食用色素主要是由兩種分子所組成

water and propylene glycol.

水還有丙二醇

These two liquids mix well so we say they are miscible,

這兩種液體可以均勻的混合，所以是可以混溶的

but they have different properties.

可是他們有不同的性質

For example, water evaporates more readily because its lighter,

舉例來說，水分子比較輕所以蒸發較快

and it has a stronger surface tension due to hydrogen bonding.

而且他也有更強的表面張力，因為它具有氫鍵

And this is important because interesting things happen when there are gradients in surface tension.

這很重要，因為當存在表面張力梯度時， 有趣的事會發生

For example, if I add some pepper to this bowl of water to allow me to see the motion,

來做個實驗，我先在這碗水裡加些胡椒好看見水的流動

and then I add a little dab of soap, right in the middle,

然後在水面中央沾一些清潔劑

you see that all of the water rushes outwards,

你可以看到所有的水都往外衝

and this is because soap has a lower surface tension than water.

這是因為清潔劑的表面張力比水小

You can think of it a bit like a tug of war.

你可以把他想成是在拔河

Before I added the soap all of those water molecules were pulling on each other equally,

在我加入清潔劑之前， 所有水分子都是以同樣的力道互相拉扯

but once I add the soap molecules in the middle,

不過當我在中間加入一些清潔劑分子

their weaker surface tension means the water molecules around them are pulling

他們較弱的表面張力代表周圍水分子拉扯的力道

harder on each other than the soap is,

比中間的清潔劑還要強

and so they rush outwards away from that spreading soap drop.

所以水分子才會快速地被往外拉，遠離中間那滴清潔劑

And this motion is called "Marangoni flow."

這種現象稱為"馬倫哥尼效應"

And a similar thing is actually happening with our food coloring droplets.

在我們的色素水滴裡面其實也有類似的效應

If you have drops of similar concentration they attract each other due to the higher humidity in-between them,

兩個濃度相近的水滴會因為彼此之間濕度較高

and they merge.

所以互相吸引融合

And although drops of different concentration also attract each other

而雖然濃度不同的水滴也會因為同樣的原因互相吸引

they don't merge when they come into contact.

他們在接觸時不會互相融合

This is because the water in the lower concentration drop

因為濃度較低的水滴裡面的水分子

pulls together and away from the drop with the higher concentration of propylene glycol,

會拉扯並遠離丙二醇濃度較高的水滴

just like with the soap and water.

就像水與清潔劑那樣

And differential evaporation drives the two drops forwards.

而蒸發速率差則推動兩個水滴前進

It is fascinating to watch these droplets and think about how closely their motion mimics life.

看著這些水滴的運動跟生命體是如此相像 實在是非常有趣

Living organisms seek out molecules like food,

有機生命體會去接近特定的分子，像是食物

and this is a process known as "chemotaxis."

這個過程稱為"趨化性"

But what these droplets are doing is really not all that dissimilar,

而這跟這些水滴的行為其實有點像

in fact its been called artificial chemotaxis.

事實上這種現象被稱為"人工趨化性"

And as amazingly life like as their motion appears,

而雖然這些水滴運動跟生命現象的相似度高的驚人

in a way, I think it shouldn't be all that surprising.

某方面來說，這其實是理所當然的

After all, evolution began with the natural tendencies of molecules:

畢竟生命演化的起源，就是這些化學分子不同的性質

to form and break apart, to attract and repel.

互相結合或崩解，互相吸引或排斥

And then over billions of years of refinement through natural selection,

而經過天擇數十億年的精煉

evolution has produced bodies whose utilisation of

演化出了複雜的生命體

these natural tendencies of molecules appears miraculous.

利用這些分子的不同性質表現出看似奇蹟的生命現象

And its that, that we call life.

這就是我們所謂的生命

I tried using slides that hadn't been passed through a flame

我有嘗試過使用沒燒過的玻片

and then I couldn't get the drops to move.

不過水滴就不動了

So on researching this further I found out that passing

經過更深入的研究，我發現

the microscope slide through the flame creates a high energy sufrace

把玻片放在火焰上燒會製造出一個高能量的表面

and what that means is, the flame is essentially breaking open some of the bonds -

意思是說，火焰會打斷一些化學鍵

the glass bonds in the surface of this slide -

那些玻璃玻片表面的化學鍵

and when you put the droplet on top,

而當你滴上水滴

Its those open bonds, its that high energy surface that

那些被打開的化學鍵製造出的高能量表面

draws some of the water molecules away from the droplet.

會把一些水分子從水滴中拉出來

And that actually makes the water molecule more likely to evaporate.

而這會讓水分子蒸發得更快

But as just happened right there, some of the microscopes,

不過就像剛剛發生的這樣

some of the microscope slides have shattered.

有些玻片會碎掉

And so you should be particularly careful when doing this procedure,

所以你在加熱的時候應該特別小心

obviously heating them up to a very high temperature causes them to expand a lot

加熱到高溫明顯的會使他們劇烈膨脹

and when they contract again as they're cooling, well then,

當他們冷卻下來要收縮的時候

they sometimes break apart because of those stresses.

過程中的壓力有時會造成玻璃碎裂