水珠在油面快速滑动的秘密（上）

This is Scientific American’s 60 Second Science. I’m Sarah Vitak.

这里是科学美国人——60秒科学系列，我是莎拉·维塔。

If you are kitchen-savvy, you probably know “the water test” method for getting stainless steel pans to the right temperature.

如果你经常下厨，你可能知道测试不锈钢平底锅是否达到合适温度的“水滴”法。

All you have to do is splash a few drops of water in a pan as it is being heated.

你要做的就是在加热时往平底锅里洒几滴水。

When the pan reaches the right temperature, instead of evaporating, the drops form into beads and skate all over the pan.

当平底锅达到合适的温度时，水滴不会蒸发，而是会形成水珠，滑过平底锅各处。

You have to do this test in an empty pan.

你必须在无油空锅里做这个测试。

And that is because, as the not-kitchen-savvy among us may have learned the hard way, mixing oil and water in a hot pan is a recipe for flying burning hot liquids.

这是因为，某些厨房小白或许有过将油与水混合在一起的惨痛经历，这会让滚烫的油水液体四处飞溅。

The phenomenon that happens when beads of water skate around in your empty pan has been understood for a long time.

人们很早就观察到了水珠在空锅里滑来滑去的现象。

Here is Dr. Kripa Varanasi from the mechanical engineering department at M.I.T. explaining it:

以下是麻省理工学院机械工程系的克里帕·瓦拉纳西博士的解释:

They’re levitating on their vapor layer with the vapor cushion that’s forming because the liquid is evaporating.

水在蒸发时会形成隔热的蒸汽层，水珠悬浮在蒸汽层上。

And so they can move around with very little friction: that’s called the Leidenfrost state.

水珠四处滑动时摩擦力极小，这种现象被称为莱顿弗罗斯特效应。

And then, if you’re at a lower temperature, you could start boiling the drop, but the drop is sticking to the surface.

如果锅里温度较低，水滴就会开始沸腾，但是它们会附着在锅面上。

But recently Dr.Varanasi and his graduate student Victor Leon set out to look at hot oil and water interactions a bit more closely.

但最近，瓦拉纳西博士和他的研究生维克多·莱昂开始更仔细地研究热油和水的相互作用。

What we found here that’s very interesting is: When you have a thin oil layer, you have the drop on it, you still can get both those states.

我们发现了非常有趣的现象: 如果锅面有一层薄薄的油层，而油层上有水珠，仍然可以得到这两种状态。

But in between, there is another state, and it can cause it to race at very high speeds on the surface.

但在两者之间，还存在另一种状态，能让水珠在锅面高速滚动。

The experiments were so simple, you could run them in your kitchen.

实验非常简单，你可以在厨房里进行。

They just used a hot plate with either a metal plate or a silicon wafer on top, then the oil (they used silicon oil), then a syringe to precisely place a water drop.

研究人员只用了一块热板，可以是一块金属板，也可以是一块硅片板，涂上油(他们使用的是硅油)，然后用注射器精确地滴下水珠。

The one thing they did a little more precisely than you would in the kitchen is that they applied the oil by spin coating, a process that creates a very thin and very uniform surface.

相比你在厨房里的实验，实验室里更精准的地方在于涂油时他们用到了旋涂法，这样能够涂出极薄且非常均匀的油层。

Their oil layer was about 10 microns, or about a hair’s width thick.

油层厚度大约为10微米，只有头发丝直径的一半。

They used high-speed imaging equipment to capture the result.

研究人员使用高速成像设备对实验结果进行成像。