B1 中級 23 分類 收藏
開始影片後,點擊或框選字幕可以立即查詢單字
字庫載入中…
回報字幕錯誤
Watch what happens when I place some small drops of food coloring on to this slide.
Some are attracted to each other and merge,
while others repel and chase each other.
It looks just like the tiny world of micro-organisms, but why?
Well if you want to try this out for yourself
You need to get some ordinary food coloring and dilute it with distilled water using a pipette.
Then pass the microscope slide through a flame for about thirty seconds.
Let it cool, and then put some drops of different concentration on to the slide.
You'll find that drops of similar concentration attract each other and merge
while drops of different concentrations chase each other.
You can draw guides on the slide using permanent marker, which is hydrophobic
and set up long distance pursuits.
Or you can find that drops of similar concentration attract each other
despite the hydrophobic barriers.
But how is this possible just using ordinary food coloring and water?
Well the key is evaporation.
Each drop is constantly evaporating, so around it is an envelope of vapour.
The rate of evaporation depends on the humidity around the drop
so the drier the air is, the faster the rate of evaporation.
So when any two drops are close enough
the humidity between them is greater than than the humidity around them,
and therefore there's more evaporation around the droplets
then in-between them,
and this pushes them together.
So differential evaporation makes the droplets attract,
but that's not the whole story.
Food coloring is a mixture of mainly two molecules,
water and propylene glycol.
These two liquids mix well so we say they are miscible,
but they have different properties.
For example, water evaporates more readily because its lighter,
and it has a stronger surface tension due to hydrogen bonding.
And this is important because interesting things happen when there are gradients in surface tension.
For example, if I add some pepper to this bowl of water to allow me to see the motion,
and then I add a little dab of soap, right in the middle,
you see that all of the water rushes outwards,
and this is because soap has a lower surface tension than water.
You can think of it a bit like a tug of war.
Before I added the soap all of those water molecules were pulling on each other equally,
but once I add the soap molecules in the middle,
their weaker surface tension means the water molecules around them are pulling
harder on each other than the soap is,
and so they rush outwards away from that spreading soap drop.
And this motion is called "Marangoni flow."
And a similar thing is actually happening with our food coloring droplets.
If you have drops of similar concentration they attract each other due to the higher humidity in-between them,
and they merge.
And although drops of different concentration also attract each other
they don't merge when they come into contact.
This is because the water in the lower concentration drop
pulls together and away from the drop with the higher concentration of propylene glycol,
just like with the soap and water.
And differential evaporation drives the two drops forwards.
It is fascinating to watch these droplets and think about how closely their motion mimics life.
Living organisms seek out molecules like food,
and this is a process known as "chemotaxis."
But what these droplets are doing is really not all that dissimilar,
in fact its been called artificial chemotaxis.
And as amazingly life like as their motion appears,
in a way, I think it shouldn't be all that surprising.
After all, evolution began with the natural tendencies of molecules:
to form and break apart, to attract and repel.
And then over billions of years of refinement through natural selection,
evolution has produced bodies whose utilisation of
these natural tendencies of molecules appears miraculous.
And its that, that we call life.
I tried using slides that hadn't been passed through a flame
and then I couldn't get the drops to move.
So on researching this further I found out that passing
the microscope slide through the flame creates a high energy sufrace
and what that means is, the flame is essentially breaking open some of the bonds -
the glass bonds in the surface of this slide -
and when you put the droplet on top,
Its those open bonds, its that high energy surface that
draws some of the water molecules away from the droplet.
And that actually makes the water molecule more likely to evaporate.
But as just happened right there, some of the microscopes,
some of the microscope slides have shattered.
And so you should be particularly careful when doing this procedure,
obviously heating them up to a very high temperature causes them to expand a lot
and when they contract again as they're cooling, well then,
they sometimes break apart because of those stresses.
提示:點選文章或是影片下面的字幕單字,可以直接快速翻譯喔!

載入中…

These Liquids Look Alive!

23 分類 收藏
林宜悉 發佈於 2020 年 3 月 29 日
看更多推薦影片
  1. 1. 單字查詢

    在字幕上選取單字即可即時查詢單字喔!

  2. 2. 單句重複播放

    可重複聽取一句單句,加強聽力!

  3. 3. 使用快速鍵

    使用影片快速鍵,讓學習更有效率!

  4. 4. 關閉語言字幕

    進階版練習可關閉字幕純聽英文哦!

  5. 5. 內嵌播放器

    可以將英文字幕學習播放器內嵌到部落格等地方喔

  6. 6. 展開播放器

    可隱藏右方全文及字典欄位,觀看影片更舒適!

  1. 英文聽力測驗

    挑戰字幕英文聽力測驗!

  1. 點擊展開筆記本讓你看的更舒服

  1. UrbanDictionary 俚語字典整合查詢。一般字典查詢不到你滿意的解譯,不妨使用「俚語字典」,或許會讓你有滿意的答案喔