内容来源：https://www.quantamagazine.org/why-is-ice-slippery-a-new-hypothesis-slides-into-the-chat-20251208/

内容总结：

冰面为何湿滑？新假说引发科学界热议

冰面湿滑，常被归因于表面存在一层薄薄的水膜。但关于这层水膜的形成原因，科学界已争论了两个世纪。近期，德国萨尔大学的研究团队提出了一项新假说，为这一经典问题带来了新视角。

传统上，主要有三种理论解释冰面湿滑现象：

1. 压力融化说：19世纪提出，认为压力会降低冰的熔点，使其表面融化。但后续计算表明，日常活动（如滑冰）产生的压力远不足以实现此效应。
2. 摩擦生热说：20世纪30年代提出，认为滑动摩擦产生的热量使冰面融化。然而实验发现，即使人静止站在冰上也可能打滑，且滑溜程度与速度无关，这对该理论构成了挑战。
3. 表面预融化说：认为冰在接触物体前，其表面就因分子排列特殊性而存在无序的“准液态”层。这虽得到广泛认同，但无法解释极低温下冰面依然湿滑的现象。

今年，德国研究团队通过计算机模拟提出了第四种假说——非晶化机制。他们发现，即使模拟系统温度极低、排除了任何融化可能，当冰面与其他材料相对滑动时，表面的水分子会被机械地“拽出”原有晶格结构，形成一层无序、类似液体的非晶态层。这层结构本身即具有润滑作用，且滑动会使其增厚。该机制尤其有望解释低温下冰的湿滑特性。

尽管新假说获得了部分学者的支持，但科学界远未达成共识。有研究者认为，前述多种机制可能在不同条件下共同作用。目前，术语使用不统一、学术交流不充分，可能成为解决这一“简单”老问题的最大障碍。冰面湿滑之谜的最终答案，仍有待进一步探索。

中文翻译：

冰面为何如此湿滑？一项新假说悄然登场。

引言

我们之所以能在溜冰场优雅滑行，或在结冰的人行道上狼狈滑倒，是因为冰的表面覆盖着一层薄薄的水状层。科学家普遍认为，正是这种具有润滑作用的液态层使冰面变得湿滑。然而，关于这层液态层形成的原因，学界始终存在分歧。

过去两个世纪里，关于这一现象主要有三种理论。今年早些时候，德国研究人员提出了第四种假说，声称能解开这个谜团。

但真相果真如此吗？共识似乎正在接近，却仍未达成。目前，关于冰面湿滑的难题依然悬而未决。

假说一：压力论

19世纪中叶，英国工程师詹姆斯·汤姆森提出：当我们踩踏冰面时，施加的压力会使冰表融化，从而形成湿滑层。通常情况下，冰在温度升至零摄氏度（32华氏度）时融化。但压力会降低冰的熔点，即使在更低温度下，冰面也可能形成水层。汤姆森的弟弟威廉（即著名的开尔文勋爵）通过实验证实了熔点与压力之间的这种理论关系。

然而到了20世纪30年代，剑桥大学物理化学实验室的弗兰克·鲍登与T·P·休斯对压力融化理论提出质疑。他们通过计算指出，普通滑雪者施加的压力远不足以显著改变冰的熔点——要达到这种效果，滑雪者体重需达数千公斤。

假说二：摩擦论

鲍登与休斯提出了另一种解释：冰面水层是由滑动物体摩擦产生的热量融化形成的。

他们在瑞士阿尔卑斯山的人工冰洞中测试该理论，用复杂装置测量冰与其他材料间的摩擦力。实验发现，与黄铜等良导热体接触时摩擦力较大，而与硬橡胶等不良导热体接触时摩擦力较小。由此他们推论：当冰面被易吸热材料摩擦时，可用于融冰的热量减少，冰面更不易打滑。这支持了摩擦生热导致冰面湿滑的理论。

尽管该解释仍见于教科书，许多科学家却持不同意见。阿姆斯特丹大学物理学家丹尼尔·波恩指出：“问题在于摩擦只能融化已滑过的冰面，而非正在滑行的冰面。”我们踏上冰面的瞬间就可能滑倒，此时尚未发生能产生摩擦热量的运动。

为验证摩擦假说，波恩团队创建了微型溜冰场。他们以不同速度旋转金属片（模拟冰刀），分别测量移动金属所需的作用力及金属对冰面的作用力。通过计算两者比值量化冰面湿滑度。科学家发现湿滑度与速度无关——而摩擦热本应随速度增加而增强——这表明摩擦生热并非冰面湿滑的主因。

假说三：预融化论

另一种可能是：冰面在接触物体前就已处于湿润状态。

1842年，英国科学家迈克尔·法拉第观察到：两块相触的冰立方会相互冻结，甚至温暖的手也会粘在冰上。他将此归因于冰表存在的薄层预融化层，该层被覆盖后会重新冻结。法拉第未能解释成因，近一个世纪后，查尔斯·格尼与沃尔德马·韦尔等科学家才提出“表面预融化”的可能机制。

他们推断冰表附近的分子行为与内部不同。冰是晶体，意味着每个水分子都被锁定在周期晶格中。但在表面，水分子缺少相邻分子束缚，因而比固态冰内部的分子更具运动自由。在这层预融化层中，分子极易被冰刀、滑雪板或鞋履推开。

如今科学家普遍承认预融化层存在（至少在接近熔点时），但对其在冰面湿滑中的作用仍有分歧。

数年前，马德里康普顿斯大学物理学家路易斯·麦克道尔团队通过系列模拟实验，检验压力、摩擦、预融化三种假说对冰面湿滑现象的解释力。“在计算机模拟中，你能看到原子运动，”他表示——这在实际实验中难以实现——“还能观察这些原子的相邻结构”，判断其呈固态周期性排列还是液态无序分布。

模拟显示：正如预融化理论预测，冰块表面确实覆盖着仅几个分子厚度的类液态层。模拟重物滑过冰面时，该层会增厚——这与压力理论吻合。最后他们验证摩擦生热效应：在冰的熔点附近，预融化层已较厚，摩擦热对其影响甚微；但在更低温度下，滑动物体产生的热量会融化冰层并使其增厚。

“我们的结论是：三种争议性假说在不同程度上同时起作用。”麦克道尔总结道。

假说四：非晶化论

或许，冰面融化根本不是其湿滑的主要原因。

近期，德国萨尔大学研究团队列举了反驳三大主流理论的依据。首先他们指出：要使压力高到足以融化冰面，滑雪板与冰的接触面积需“小到不合理”。其次实验表明，以实际速度滑行的滑雪板产生的摩擦热量不足以引发融化。第三，他们发现极寒条件下即使没有预融化层，冰面依然湿滑。（表面分子虽仍缺少相邻分子束缚，但在低温下缺乏足够能量挣脱固态冰分子的强键合力。）团队成员材料科学家阿什拉夫·阿提拉表示：“因此冰面湿滑要么是多种因素共同作用的结果，要么存在我们尚未知晓的其他机制。”

科学家从钻石等其他物质的研究中寻找新解释。宝石抛光师凭经验早知钻石某些晶面更易抛光（即“更软”）。2011年，另一德国研究团队发表论文解释该现象：他们模拟两颗钻石相互滑动时，表面原子受机械力脱离键合，得以移动并形成新键合。这种滑动会形成无序的“非晶”层——与钻石晶体结构不同，该层呈无序态，性质更接近液体而非固体。这种非晶化效应取决于表面分子取向，因此晶体某些晶面更软。

阿提拉团队认为冰中存在类似机制。他们模拟两个冰面相互滑动，并将系统温度控制在足够低温以确保无融化发生（因此任何湿滑现象都需另寻解释）。初始阶段，冰面如磁铁般相互吸引——这是因为水分子是偶极子，正负电荷分布不均，一个分子的正极会吸引另一个分子的负极。这种吸引力在滑动界面间形成微小焊点。随着冰面相对滑动，焊点断裂与新焊点形成交替发生，逐渐改变冰的结构。

团队用其他亲水或疏水材料替换其中一个冰面重复模拟。结果再次显示：冰表分子随滑动发生位移，且当另一物质吸引冰面时位移更显著。

模拟表明：滑动会机械性破坏冰的有序晶格，形成随滑动持续增厚的非晶层。研究团队认为，这才是冰面湿滑（尤其在低温下）的真正原因，而非融化所致。

悬而未决的共识

麦克道尔认可阿提拉团队的研究结果，但他认为非晶化仅发生在高速滑动时（原作者持异议，但模拟低速滑动需要极高的计算资源）。波恩也支持新解释，称其与团队2021年开展的冰面滑动实验研究相符。这些实验与新模拟均指向冰面湿滑源于表面结构变化，尽管研究者对现象的描述角度不同：阿提拉强调水分子的机械位移驱动变化，波恩则关注表面分子初始流动性。他将冰表比作铺满小球的房间：“因其高度易动，身处其中根本无法保持平衡，正如在冰面上难以站稳。”

波恩认为双方描述差异“只是语义问题”，但阿提拉的合著者谢尔盖·苏霍姆利诺夫反对此说：“即便表象相似，我相信这是不同的机制。”

我们无疑正逼近这个看似简单、困扰学界数百年的谜题答案。当前，研究者之间缺乏统一术语可能是解决问题的最大障碍之一——相似效应被赋予不同名称，催生出相异假说。波恩还指出：“冰研究者确实存在分歧甚至对立观点，但他们并未真正坦诚交流彼此异议。”

英文来源：

Why Is Ice Slippery? A New Hypothesis Slides Into the Chat.
Introduction
The reason we can gracefully glide on an ice-skating rink or clumsily slip on an icy sidewalk is that the surface of ice is coated by a thin watery layer. Scientists generally agree that this lubricating, liquidlike layer is what makes ice slippery. They disagree, though, about why the layer forms.
Three main theories about the phenomenon have been debated over the past two centuries. Earlier this year, researchers in Germany put forward a fourth hypothesis that they say solves the puzzle.
But does it? A consensus feels nearer but has yet to be reached. For now, the slippery problem remains open.
Hypothesis 1: Pressure
In the mid-1800s, an English engineer named James Thomson suggested that when we step on ice, the pressure we exert melts its surface, making it slippery. Under normal conditions, ice melts when the temperature rises to zero degrees Celsius (32 degrees Fahrenheit). But pressure lowers its melting point, so that even at lower temperatures, a layer of water might form on the surface. This theoretical relationship between melting point and pressure was experimentally confirmed by Thomson’s younger brother William, better known as Lord Kelvin.
In the 1930s, though, Frank P. Bowden and T.P. Hughes of the Laboratory of Physical Chemistry at the University of Cambridge cast doubt on the pressure melting theory. They calculated that an average skier exerts way too little pressure to significantly alter ice’s melting point. To do so, the skier would have to weigh thousands of kilograms.
Hypothesis 2: Friction
Bowden and Hughes suggested an alternative explanation for the formation of the water layer: that it melts because of heat generated by friction caused by whatever is sliding against it.
They tested their theory in an artificial ice cave in the Swiss Alps, using a complex contraption to measure the friction between ice and other materials. They found that the friction was higher with materials that are good at conducting heat, such as brass, than with poor conductors like ebonite. From this, they concluded that when ice is rubbed by a material that easily absorbs heat, less heat is available to melt the ice, making it less slippery. This supported their theory that frictional melting is responsible for ice’s slipperiness.
Although this explanation still appears in textbooks, many scientists disagree with it. “The problem with that is you only melt the ice behind you, not the ice you are actually skating on,” said Daniel Bonn, a physicist at the University of Amsterdam. Ice can be slippery the moment we step on it, before any motion has occurred that could cause frictional heating.
To test the friction hypothesis, Bonn and his team created a microscopic ice-skating rink. They rotated a piece of metal (standing in for the blade of a skate) at different speeds, each time measuring the force required to move the metal and the force that the metal exerted on the ice. The ratio of these forces gave them a measure of the ice’s slipperiness. The scientists found that the slipperiness did not depend on the speed, suggesting that frictional heating — which should increase with speed — isn’t what makes ice slippery.
Hypothesis 3: Premelting
There’s another possibility: that ice’s surface is wet even before anything makes contact with it.
In 1842, the English scientist Michael Faraday observed that two touching ice cubes will freeze to each other, and even a warm hand will stick to ice. He attributed this phenomenon to a thin, premelted layer that sits on ice’s exposed surface, and that freezes again when covered up. Faraday couldn’t explain why it happens, and it took almost a century for other scientists — notably Charles Gurney and Woldemar Weyl — to propose why “surface premelting” might occur.
They intuited that the molecules near the surface behave differently from those deep within the ice. Ice is a crystal, which means each water molecule is locked into a periodic lattice. However, at the surface, the water molecules have fewer neighbors to bond with and therefore have more freedom of movement than in solid ice. In that so-called premelted layer, molecules are easily displaced by a skate, a ski or a shoe.
Today, scientists generally agree that the premelted layer exists, at least close to the melting point, but they disagree on its role in ice’s slipperiness.
Nathaniel Noir
A few years ago, Luis MacDowell, a physicist at the Complutense University of Madrid, and his collaborators ran a series of simulations to establish which of the three hypotheses — pressure, friction or premelting — best explains the slipperiness of ice. “In computer simulations, you can see the atoms move,” he said — something that isn’t feasible in real experiments. “And you can actually look at the neighbors of those atoms” to see whether they are periodically spaced, like in a solid, or disordered, like in a liquid.
They observed that their simulated block of ice was indeed coated with a liquidlike layer just a few molecules thick, as the premelting theory predicts. When they simulated a heavy object sliding on the ice’s surface, the layer thickened, in agreement with the pressure theory. Finally, they explored frictional heating. Near ice’s melting point, the premelted layer was already thick, so frictional heating didn’t significantly impact it. At lower temperatures, however, the sliding object produced heat that melted the ice and thickened the layer.
“Our message is: All three controversial hypotheses operate simultaneously to one or the other degree,” MacDowell said.
Hypothesis 4: Amorphization
Or perhaps the melting of the surface isn’t the main cause of ice’s slipperiness.
Recently, a team of researchers at Saarland University in Germany identified arguments against all three prevailing theories. First, for pressure to be high enough to melt ice’s surface, the area of contact between (say) skis and ice would have to be “unreasonably small,” they wrote. Second, for a ski moving at a realistic speed, experiments show that the amount of heat generated by friction is insufficient to cause melting. Third, they found that in extremely cold temperatures, ice is still slippery even though there’s no premelted layer. (Surface molecules still have a dearth of neighbors, but at low temperatures they don’t have enough energy to overcome the strong bonds with solid ice molecules.) “So either the slipperiness of ice is coming from a combination of all of them or a few of them, or there is something else that we don’t know yet,” said Achraf Atila, a materials scientist on the team.
The scientists looked for alternative explanations in research on other substances, such as diamonds. Gemstone polishers have long known from experience that some sides of a diamond are easier to polish, or “softer,” than others. In 2011, another German research group published a paper explaining this phenomenon. They created computer simulations of two diamonds sliding against each other. Atoms on the surface were mechanically pulled out of their bonds, which allowed them to move, form new bonds, and so on. This sliding formed a structureless, “amorphous” layer. In contrast to the crystal nature of the diamond, this layer is disordered and behaves more like a liquid than a solid. This amorphization effect depends on the orientation of molecules at the surface, so some sides of a crystal are softer than others.
Atila and his colleagues argue that a similar mechanism happens in ice. They simulated ice surfaces sliding against each other, keeping the temperature of the simulated system low enough to ensure the absence of melting. (Any slipperiness would therefore have a different explanation.) Initially, the surfaces attracted each other, much like magnets. This was because water molecules are dipoles, with uneven concentrations of positive and negative charge. The positive end of one molecule attracts the negative end of another. The attraction in the ice created tiny welds between the sliding surfaces. As the surfaces slid past each other, the welds broke apart and new ones formed, gradually changing the ice’s structure.
The scientists repeated the simulations, replacing one of the ice surfaces with other materials that are either attracted or repelled by water. Again, molecules on the surface of the ice were displaced with sliding, but more so when the other substance attracted the ice.
The simulations indicated that sliding mechanically destroys the ordered crystal lattice of ice, creating an amorphous layer that thickens as the sliding goes on. The team says that this, rather than melting, explains ice’s slipperiness — especially at low temperatures.
A Consensus Kept on Ice
MacDowell trusts the results from Atila and collaborators, although he thinks amorphization occurs only at high sliding speeds (the authors disagree, but simulating low sliding speeds requires a prohibitive amount of computational power).
Bonn also supports the new explanation, which he says aligns with experimental studies of objects sliding on ice conducted by his group in 2021. Those experiments and the new simulations both suggest that ice is slippery because of structural changes in its surface, though the researchers characterize what’s happening in different terms. Atila believes that the changes are driven by the mechanical displacement of water molecules, whereas Bonn focuses on how mobile the surface molecules are to begin with. He compares the surface to a floor filled with little balls: “Because they’re so mobile, it’s impossible to stay upright if you’re in such a room. Just as it’s very difficult to stay upright when you’re on ice.”
The difference between their descriptions “is a semantic issue,” according to Bonn, but Atila’s co-author Sergey Sukhomlinov disagrees. “I believe these are different mechanisms, even though they may look similar,” he said.
We’re surely getting closer to settling the seemingly simple, centuries-old question of why ice is slippery. At this point, the lack of a shared vocabulary among researchers might be one of the biggest hindrances to resolving the issue. Similar effects might get different names, suggesting different hypotheses. Bonn also blames the fact that “ice researchers do have different and contradictory opinions, but they don’t really tell each other that they disagree with each other.”