Geckos seem to defy gravity, scaling vertical surfaces and walking upside down without claws, adhesive glues or super-powered spiderwebs.

壁虎看來好像可以抵抗地心引力、攀爬垂直表面，甚至能不依靠爪子、黏著劑或力量很強大的蜘蛛網頭下腳上走路。

Instead, they take advantage of a simple principle: that positive and negative charges attract.

牠們利用的，反而是一個簡單的原理：正電荷和負電荷相吸。

That attraction binds together compounds, like table salt, which is made of positively charged sodium ions stuck to negatively charged chloride ions.

這個吸引力把化合物結合在一起，例如食鹽，是由帶正電的鈉離子黏著帶負電的氯離子構成。

But a gecko's feet aren't charged and neither are the surfaces they're walking on.

但是，壁虎的腳並沒有帶電，牠們攀爬的表面也沒有。

So, what makes them stick?

那麼，是什麼東西讓壁虎的腳可以有黏性呢？

The answer lies in a clever combination of intermolecular forces and structural engineering.

答案就在分子間的作用力和結構工程的巧妙結合。

All the elements in the periodic table have a different affinity for electrons.

元素週期表裡的所有元素都有不同的電子親和力。

Elements like oxygen and fluorine really, really want electrons while elements like hydrogen and lithium don't attract them as strongly.

元素如氧和氟，真的很想要電子，而元素如氫和鋰，則沒有那麼想要電子。

An atom's relative greed for electrons is called its electronegativity.

原子對電子的相對吸引力，稱為電負度 (隱電性／負電性)。

Electrons are moving around all the time and can easily relocate to wherever they're wanted most.

電子總是到處移動，而且很輕易地搬遷到任何它們最想要去的地點。

So when there are atoms with different electronegativities in the same molecule, the molecules cloud of electrons gets pulled towards the more electronegative atom.

所以，當同一個分子裡有不同的電負度原子時，電子雲便會向電負度較高的原子靠近。

That creates a thin spot in the electron cloud where positive charge from the atomic nuclei shines through, as well as a negatively charged lump of electrons somewhere else.

這在電子雲中產生了一個薄薄的區塊，在這裡原子核裡的正電荷及負電的電子塊皆自由移動。

So the molecule itself isn't charged, but it does have positively and negatively charged patches.

分子本身是不帶電的，但它確實有帶正電板和帶負電板。

These patchy charges can attract neighboring molecules to each other.

這些電板可以彼此互相吸引鄰近的分子。

They'll line up so that the positive spots on one are next to the negative spots on the other.

它們會排成一列 ，而正極的那一端會對著另一個分子的負極端。

There doesn't even have to be a strongly electronegative atom to create these attractive forces.

基本上，根本不需要強烈的電負度原子來產生這些吸引力。

Electrons are always on the move, and sometimes they pile up temporarily in one spot.

電子總是在移動，有時它們會暫時聚集在某一個區塊。

That flicker of charge is enough to attract molecules to each other.

那帶電量足夠讓分子相互吸引。

Such interactions between uncharged molecules are called van der Waals forces.

這種未帶電分子之間的相互作用，叫做「凡德瓦力」。

They're not as strong as the interactions between charged particles, but if you have enough of them, they can really add up.

雖然不如帶電粒子之間的相互作用那麼強烈，但是，假如有足夠的未帶電分子，它們也能產生強大的「凡德瓦力」。

That's the gecko's secret.

那就是壁虎的秘密。

Gecko toes are padded with flexible ridges.

壁虎的腳趾上襯著富有彈性的脊。

Those ridges are covered in tiny hair-like structures, much thinner than human hair, called setae.

而這些彈性脊上佈滿了像毛髮般細小的結構，是比人類頭髮纖細更多的毛，叫「剛毛」。

And each of the setae is covered in even tinier bristles called spatulae.

每一根剛毛上又覆蓋了更細小的刷毛，叫「鏟狀匙突」。

Their tiny spatula-like shape is perfect for what the gecko needs them to do: stick and release on command.

這些像小鏟子般的「鏟狀匙突」，正是壁虎所需要的：依照大腦指令黏住和放開。

When the gecko unfurls its flexible toes onto the ceiling, the spatulae hit at the perfect angle for the van der Waals force to engage.

當壁虎在天花板上撐開牠的富有彈性的趾頭時，腳趾上的鏟狀匙突會打開剛好的角度，讓「凡德瓦力」發揮作用。

The spatulae flatten, creating lots of surface area for their positively and negatively charged patches to find complimentary patches on the ceiling.

當鏟狀匙突變平坦時，會產生很多表面積，能夠讓帶正電板和帶負電板在天花板上找到彼此。

Each spatula only contributes a minuscule amount of that van der Waals stickiness.

每一個鏟狀匙突只貢獻極小的「凡德瓦力」黏著力。

But a gecko has about two billion of them, creating enough combined force to support its weight.

但一隻壁虎有約二十億個鏟狀匙突，能產生足夠的結合力可以來支撐牠的重量。

In fact, the whole gecko could dangle from a single one of its toes.

事實上，一根腳趾便能支撐整隻壁虎的重量。

That super stickiness can be broken, though, by changing the angle just a little bit.

不過，那超級黏性也有被破壞的可能，只要角度稍為改變一點的話。

So, the gecko can peel its foot back off, scurrying towards a meal or away from a predator.

所以，壁虎可以從行走的表面脱落，然後快速地接近牠的獵物，或是逃離牠的掠捕者。

This strategy, using a forest of specially shaped bristles to maximize the van der Waals forces between ordinary molecules has inspired man-made materials designed to imitate the gecko's amazing adhesive ability.

這個策略，利用一大片的特殊形狀刷毛，在普通分子之間，將「凡德瓦力」發揮到最大，啟發人類設計出仿壁虎驚人黏性力的人造材料。

Artificial versions aren't as strong as gecko toes quite yet, but they're good enough to allow a full-grown man to climb 25 feet up a glass wall.

人造版本的黏性度還沒有壁虎腳趾的黏性度好，但是它也已經足夠讓一個成年人在玻璃牆上爬行 25 呎。

In fact, our gecko's prey is also using van der Waals forces to stick to the ceiling.

事實上，壁虎的獵物也是利用「凡德瓦力」停在天花板上。

So, the gecko peels up its toes and the chase is back on.

因此，壁虎移動牠的腳趾繼續和牠的獵物展開追逐大戰。