We FINALLY Proved Why Ice Is Slippery

Summary

视频脚本探讨了冰的奇特性质：冰的表面异常滑，以及冰块如何短暂地融合成一体。通过原子力显微镜（AFM）的先进技术，研究者首次揭示了冰表面的分子结构。发现冰的表面存在一种类似液体的松散分子层，这可能是冰滑的主要原因。视频还讨论了历史上关于冰滑性的误解和现代研究的发现，解释了冰在不同温度下摩擦系数的变化，以及冰的“预熔”现象，为理解冰的滑性提供了复杂的科学解释。

Takeaways

• 🧊 冰的表面具有独特的滑性，这与固体的一般性质不同。
• 🔍 科学家使用原子力显微镜（AFM）首次观察到冰表面的分子结构。
• 📚 历史上，人们曾认为冰的滑性是因为表面覆盖了一层液态水。
• 🚫 然而，在极端真空条件下，即使没有液态水层，冰仍然保持滑性。
• 🔬 研究发现冰的表面分子结构与内部不同，表面分子排列较为松散。
• 🔄 冰的表面存在一种类似液态的层，但并非真正的液态，这可能是滑性的原因。
• 🌡️ 冰的滑性与温度有关，研究发现在-7°C时滑性最强。
• 🤔 冰的滑性可能与表面分子的自由度有关，这些分子仅通过较少的氢键连接。
• 🏒 冰的滑性对冬季运动有重要影响，不同运动对冰面温度有不同的偏好。
• 🔄 冰的表面在不同温度下会经历结构变化，这影响了其滑性。
• 🌍 冰的这种不寻常的物理行为是地球上最常见的材料之一的独特特性。

Q & A

为什么冰块能够在短时间内粘在一起变成一个单一物体？

冰块在短时间内粘在一起是因为冰的表面分子具有较低的结合力，可以形成一种准液态层，这使得冰块在接触时能够暂时粘附。

冰的表面为什么特别滑？

冰的表面特别滑是因为在冰的外层存在一种准液态层，这层分子的结合力较弱，可以自由移动，类似于在冰面上滑动的弹珠。

科学家是如何观察到冰分子的表面结构的？

科学家使用原子力显微镜（AFM）这种极其灵敏的技术，能够感知到单个原子之间的空间，从而首次获得了冰表面结构的图像。

为什么在极端真空条件下，冰仍然保持滑性？

即使在没有液体水分子的极端真空条件下，冰仍然保持滑性，这是因为冰的表面存在一种由分子结构不规律造成的准液态层。

历史上有哪些科学家尝试解释冰的滑性？

历史上，包括迈克尔·法拉第（Michael Faraday）和约翰·乔利（John Joly）在内的科学家都曾尝试通过实验来解释冰的滑性。

为什么冰在压力作用下会融化形成滑层，但两块冰相互接触时却会冻结？

冰在压力作用下会融化形成滑层是因为压力降低了冰的熔点，但在两块冰相互接触时，由于没有足够的压力来降低熔点，它们会因为表面分子的结合而冻结。

冰的滑性是否与摩擦产生的热量有关？

虽然摩擦会产生热量，可能导致冰融化形成滑层，但实际经验表明，即使在没有明显运动的情况下，冰也会滑，这表明冰的滑性可能与更深层次的分子结构有关。

原子力显微镜（AFM）是如何工作的？

AFM通过一个极细的探针在材料表面移动，利用激光反射来放大探针的微小运动，从而测量探针尖端在原子层面上的高低变化，生成材料表面的原子级图像。

冰的表面分子是如何排列的？

冰的表面分子通常以六角形层状排列，形成一种称为IH的冰相，但在不同冰相的交界处，分子的排列较为混乱，指向外部的氢原子较多。

冰的滑性是否与温度有关？

是的，冰的滑性与温度有关。在2018年的实验中发现，冰在-7°C时滑性最大，这也是速滑冰场通常使用的温度。

为什么冰在-100°C时的摩擦力会增加？

在极低温度下，冰表面的准液态层分子运动减缓，导致冰的表面变得更加坚硬，摩擦力因此增加。

Outlines

00:00

🧊 冰的奇异性质

本段介绍了冰的两个不寻常的特性：其表面异常滑和冰块能瞬间融合。传统上认为冰滑是因为表面有一层液态水，但实验显示即使在真空中，冰依然滑。19世纪的科学家们通过实验和理论探讨了冰的这些特性，包括水分子在冰中的排列方式以及冰的密度为何低于液态水。此外，还提到了大气压力对冰熔点的影响以及冰在不同压力和温度下的行为。

05:02

🔬 原子力显微镜下的冰表面

科学家们使用原子力显微镜（AFM）首次观察到冰表面的分子结构。在极低温和真空条件下，发现冰表面存在一种准液态层，由松散结合的水分子组成，这些分子不像固体那样固定，也不像液体那样自由。这种结构在冰的两种相——六角冰（IH）和立方冰（IC）——的交界处尤为明显，这些分子的氢原子通常向外指向，可能与冰的滑性有关。此外，还讨论了温度如何影响冰的滑性，以及冰在不同温度下摩擦系数的变化。

10:02

🌡️ 冰的滑性与温度的关系

本段深入探讨了冰的滑性与其表面分子结构和温度的关系。2018年的研究表明，冰在0°C时非常滑，但在-100°C时摩擦力增大。这解释了为何在极低温度下AFM能捕捉到清晰的冰表面图像。随着温度的升高，冰表面的立方相（IC）增长，水分子的移动性增加，这与摩擦系数的变化相匹配。冰的滑性在-7°C时达到最大，这与速度滑冰场地的温度一致。视频最后提出了一个关于冰滑性的复杂答案：冰是一种固体，但其表面有一层可以像弹珠一样移动的分子，这种特性在自然界中极为罕见。

Keywords

💡冰的粘接性

冰的粘接性指的是两块冰在接触时能够迅速粘在一起的特性。在视频中，这与冰的表面特性有关，是视频探讨的中心主题之一。例如，视频中提到冰的粘接性与冰的表面滑性有关，这是通过原子力显微镜(AFM)观察到的现象。

💡滑性

滑性是指物体表面允许其他物体在其上滑动的特性。视频中探讨了冰的滑性，解释了为什么冰的表面比其他固体更滑。例如，提到了冰的滑性与表面的水分子排列有关，这些分子在冰的表面形成了一种准液态层。

💡原子力显微镜(AFM)

原子力显微镜是一种能够观察和测量材料表面原子级别的高度变化的仪器。视频中提到使用AFM来观察冰的表面，揭示了冰表面分子的特殊排列方式，这对于理解冰的滑性至关重要。

💡水分子

水分子是构成冰和水的基本单元，由两个氢原子和一个氧原子组成。视频中讨论了水分子在冰的表面如何排列，以及它们如何通过氢键相互作用，形成冰的固体结构和表面的准液态层。

💡氢键

氢键是一种较弱的化学键，通常在氢原子和电负性较大的原子（如氧）之间形成。视频中解释了氢键在冰的固体结构中的作用，以及在冰的表面如何影响水分子的排列和移动。

💡冰的表面结构

冰的表面结构指的是冰表面水分子的排列方式。视频中提到，冰的表面存在两种不同的冰相：六角形的IH冰和立方体的ICC冰，它们的边界处存在分子取向的不规则性，这可能与冰的滑性有关。

💡准液态层

准液态层是指冰表面的一种特殊状态，这里的水分子不像固体中的分子那样固定，也不像液体中的分子那样自由移动。视频中提到，这种准液态层可能是冰表面滑性的原因。

💡压力熔化

压力熔化是指在压力作用下，冰的熔点降低，从而使冰熔化成水的现象。视频中讨论了这一概念，并指出它不能完全解释冰的滑性，因为即使在真空中没有液体层的情况下，冰仍然保持滑性。

💡摩擦

摩擦是指两个接触表面在相对运动时产生的阻碍运动的力。视频中提到，摩擦与冰的滑性有关，但摩擦产生的热量并不能完全解释冰的滑性，因为即使在没有明显摩擦的情况下，冰也能保持滑性。

💡预熔

预熔是指在冰开始熔化成水之前，表面分子的某些变化。视频中提到，随着温度的升高，冰的表面结构会发生变化，这可能影响冰的滑性，例如在-7°C时冰的滑性达到最大。

💡温度依赖性

温度依赖性指的是物质的性质随着温度变化而变化的特性。视频中提到，冰的滑性具有温度依赖性，即在不同的温度下，冰的滑性会有所不同，这与冰表面分子的行为有关。

Highlights

冰块的粘附现象：冰块在接触时能够短暂地融合成单个物体。

冰的表面异常滑：冰的滑性与固体的一般性质不同，其表面滑性令人费解。

原子力显微镜（AFM）的使用：研究团队利用AFM技术首次观察到冰的表面分子排列。

冰的滑性与水分子的排列：水分子在冰表面形成非规则排列，可能与冰的滑性有关。

冰的表面分子结构：冰表面存在六角形和立方体两种冰相的分子。

冰的表面分子动态：表面水分子由于氢键数量减少而具有较高的活动性。

冰的滑性与温度的关系：冰在-7°C时滑性最大，这与速滑运动中使用的温度一致。

冰的表面分子的准液态层：表面分子可能形成一种介于固体和液体之间的状态。

冰的滑性与压力的关系：压力对冰的滑性影响有限，与之前的理论不符。

冰的滑性与摩擦的关系：摩擦产生的热量并不能完全解释冰的滑性。

冰的表面分子的动态变化：温度升高时，冰表面分子的排列和活动性发生变化。

冰的表面分子的非均匀性：冰表面分子的排列在不同区域存在差异。

冰的滑性与液态水层的关系：液态水层的存在可能使冰的滑性降低。

冰的表面分子的动态模拟：通过AFM技术观察到冰表面分子的动态行为。

冰的滑性与冰相变化的关系：冰的滑性可能与冰的相变过程有关。

冰的表面分子的排列对滑性的影响：冰表面分子的非规则排列可能是滑性的关键。

冰的滑性的复杂性：冰的滑性是一个涉及多种因素的复杂现象。

Transcripts

ice is weird just by holding together

two blocks of ice only for a second they

fuse to become a single object this as a

property of solids is reasonably

uncommon at least in my experience so

how is this possible let me know what

you think but the answer is more

complicated than it seems and it relates

to another strange property of ice that

occurs at its surface it's seemingly

unreasonable level of slipperiness

me just enjoying a freeze is coming we

have been debating the quirks of Ice's

surface for a long time but to get a

good understanding of it you really want

to be able to see what the individual

water molecules are doing this sounds

obviously like it should be impossible

and it has been until now the research

team has just released their findings in

the scientific journal Nature collected

using a technique that is so sensitive

it can feel the space between individual

atoms and produce for the very first

time a picture of Ice's surface but to

really understand what this picture

tells us and why ice is slippery we need

to Rewind by about 160

years on its surface ice being slippery

makes sense when water is spilled on the

floor it becomes a slip Hazard we reason

this is because water creates a mobile

barrier between our foot and the floor

almost just like stepping on a bunch of

marbles that tumble along and cause you

to slip you might guess maybe ice is so

slippery because it too is covered in a

thin layer of liquid water maybe the

answer is as simple as that in fact in

the late 1850s Michael Faraday one of

the most influential scientists in

history particularly across

electromagnetism electrochemistry tried

this exact experiment and concluded the

very same thing which he announced in a

talk at the Royal Society however there

is a problem with this theory if you can

conduct this experiment under extreme

vacuum where no liquid layer can be

present because liquid water molecules

would have evaporated away as there is

no atmosphere holding them down then Ice

Still Remains slippery so what's

actually

[Music]

happening believe it or not ice science

was all the rage through the mid 1800s

to early 1900s partially inspired by the

other observation we've all made water

as a liquid is denser than water as a

solid which which is why ice floats on

liquid water this it turns out is a

really rare property across materials

with bismuth being one of the very few

similar exceptions for water this is the

result of the crystal structure water

forms as it freezes the hydrogen bonds

that rapidly connect and disconnect from

nearby Neighbors in liquid water as it

begins to freeze the molecules of H2O

arrange to form bonds in such a way they

create additional space between the

molecules so the same volume of water

expands by about 10% as it goes from

liquid to solid in the 1850s James

Thompson an Irish mathematician and

engineer was examining the change from

liquid to solid and noticed that the

freezing temperature changed based on

atmospheric pressure Thompson was one of

The Inspirations of the field of

thermodynamics something I'll never

personally forgive him for but his work

did lead us to developing this useful if

somewhat complicated looking phase

diagram of water's Behavior here we see

what Thompson saw we can cause ice to

melt and become water either by

increasing the temperature or by

increasing the pressure maybe ice can be

slippery in a vacuum even if it's liquid

layer evaporates away because as soon as

we go to touch it to measure its

slipperiness the pressure of that touch

melts the surface and creates a newly

slippery liquid layer in 1886 John Jolie

followed the same reasoning to suggest

how ice skaters might Glide across

frozen lakes Jolie suggested that the

pressure of a thin ice skates blade is

so great because it touches ice on such

a small area that it melts the ice to

water creating a slipping layer in

theory a good suggestion earning him the

nickname John Bon Jolie however while

the basic idea is correct you can melt

ice by pressurizing it the numbers don't

really work at all 150 lb person

standing on Ice wearing a pair of ice

skates exerts a pressure of roughly 50

lb per square in on the ice that amount

of pressure lowers the melting

temperature from 0 to -0.01

16666 repeating de C or for Americans

32° F down to 31.9 7° fah if this

explanation was in fact correct light

objects or ones with large surface area

like a hockey park or a ski would create

even lower pressure and shouldn't slip

at all and that's a problem because in

fact we see the exact opposite many

winter sports are best below freezing

temperature figure skaters prefer - 5.5

de C for a slower softer ice to land

their tricks on whereas hockey players

like the cold hard and fast conditions

of - 9° c speed skaters like somewhere

in between at -7° C this is also

disproved as a primary mechanism by our

first experiment when we press two

blocks of ice together they freeze why

would an ice skate against ice become

slippery but ice against ice freezes

despite this hypothesis's shortcomings

it Remains the dominant EXP of

slipperiness of ice for over a century

including many YouTube videos about it

so if pressure is not responsible what

else could be maybe it's heat generated

from

friction two surfaces in contact moving

relative to each other produce heat

could this heat be melting the ice to

form the slippery liquid layer now this

will of course happen to some extent but

most practical experience tells us we

don't have to be moving much to slip

instead it feels very much like the

phenomenon that is producing this

slipping is already present without

pressure and without friction and

without heating being required if this

idea of a liquid water layer can't fully

explain why ice is so slippery maybe

it's something that behaves like a

liquid but isn't one and isn't a solid

either when we described the freezing of

water into ice we talked about the

hydrogen bonds aligning within the bulk

material to create a solid less dense

than the liquid phase all of the

molecules were held in rigid formation

supported by the network of surrounding

molecules which are similarly locked in

position this is true everywhere within

a solid except for at the surface where

the supportive crystal structure extends

below but above the outermost layer of

water molecules interact with nothing

but the atmosphere or whatever object

they come in contact with it was at this

surface that researchers directed their

focus using a piece of equipment called

an atomic Force microscope or AFM which

here is a no expense spared mockup of

one the AFM has a long caner lever about

100 to 500 microns long or about the

length of the diameter of two human

hairs side by side it's about 30 to 50

microns wide which is half of the

diameter of a grain of sand and around

0.5 to 0.8 microns thick which about the

thickness of a red blood cell I used AFM

probes a lot in my PhD and although they

are metal they are so thin that it's

better to think of them as a blade of

grass fluttering on the Wind than a

piece of metal at the end of the canala

there is a tip that is usually

triangular and goes from quite wide at

its base to at its end point just the

width of a single atom You could argue

very reasonably that AFM tips are the

sharpest objects in the world this AFM

probe is attached to the atomic Force

microscope itself which then drags the

probe along the atomic surface of a

material here represented by these

marbles in a tray and it measures or

really feels the change in height of the

tip as it travels over over the surface

of the individual atoms but how do you

sense or feel the bump of going over

just a single atom even though the

height change is absolutely tiny by

reflecting a laser beam off of the back

of the caner lever and detecting the

position of that laser beam a long way

away this amplifies the up and down

motion of the caner lever and allows you

to measure the bump of going over an

atom as well as the gaps in between

atoms on a Surface this produces images

of atoms that look like this the

research team conducted their experiment

at Min

-150° C and in a near perfect vacuum

with at the very tip a single carbon

monoxide molecule under normal

conditions they found that the water

molecules are arranged like this in

layers of hexagons stacked one on top of

the other a phase of ice called IH for

hexagonal ice this ice type typically

features the oxygen molecule of the H2O

facing outward however there are also

small clusters of a secondary ice type

cubic in nature called ICC no pun

intended and the interesting thing

happens at the boundaries between these

two ice phases rather than the neatly

arranged uniform oxygen facing outward

molecular orientation as these two types

of ice don't nicely interface together

there's a perimeter of water molecules

between the two that aren't quite sure

whether to orient in a hexagonal or

cubic structure and so kind of end up

doing their own thing usually pointing

their hydrogen atom outward away from

the Ice's surface this is the very first

time we've been able to image the

surface of ice to this level of detail

and see exactly the orientations of the

atoms within the water molecules but

what do these findings actually mean

this break-in structure this disorder

not prevented or tamed like it is deeper

within the solid creates a collection of

loosely bound molecules on the surface

of the ice only held by a reduced number

of hydrogen bonds the suggestion is that

these Loosely bound molecules can move

with freedom not usually experienced by

a solid but aren't quite as free as a

liquid either this quasi liquid layer

May detach and reattach to the surface

acting as we first imagined like a layer

of marbles able to shift and move

creating one of the only solids in the

world that slips but the story is more

complicated still as I looked at these

images there was something that confused

me if you've run an AFM before you'll be

thinking the same thing how do you drag

your AFM tip over something that's

slipping around on the surface during my

PhD I used to image nanop particles on

glass surfaces that I hoped were fixed

in place but sometimes they would detach

and what I would image would be a flat

plane with a sudden and long line in it

as I dragged the atoms along with the

movement of the tip why don't we see

these water molecules slipping around

like the marbles that we described them

to be I had to dig around to find out

but I found a research paper that gives

us a clue back in 2018 a team of

research led by Professor Daniel Bon

from the University of Amsterdam through

macroscopic friction experiments at

temperatures ranging from 0 C to- 100° C

showed that surprisingly ice goes from

extremely slippery as a surface at

around 0° C to a high friction surface

at -100° C this is why the AFM

experiment conducted at an even colder

minus 150 was able to capture such a

clear image it's so cold here the

slippery water molecule marbles are

frozen in place these AFM images also

reveal something else as the researchers

increased the temperature the cubic

phase grew across the surface as a

temperature increased the increased

thermal energy drives a change in the

mobility of the topmost water molecules

this matches the temperature dependence

of the measured change in friction from

that 2018 paper this phenomenon is part

of a process called pre-melting the the

process that happens before solid ice

melts into liquid water and actually

upon melting as soon as a real liquid

layer forms on it it actually becomes

less slippery as the highly structured

solid ice becomes more easily deformed

the experiments in 2018 showed that the

slipperiness of ice is actually at its

maximum at -7° C the temperature

typically used in speed skating rinks

putting this all together this is a very

complicated answer to a very simple

question of why is I slippy it's a solid

with an outermost layer that is free to

move like marbles across its surface

liquid like in nature but actually when

a liquid layer is present that becomes

less slippery than the solid an

incredibly uncommon behavior from one of

the most common materials on

Earth I love that sometimes it's the

simplest questions that make us scratch

our heads the hardest if if you like

this video you might be interested in a

similar simple question with an answer

that we actually aren't quite sure about

where does gold actually come from as

always thank you very much for watching

I'll see you next week

goodbye okay do you know how hard it was

to get these two ice cubes to actually

stick together you have to become a

single

block they stick who they to become a

single block my fing fingers are so

cold block they don't they don't stick

what's happening they turn into a