石墨烯看不见水

石墨烯涂层铜的测试设置

There is virtually no change in the way water interacts with materials including copper, gold, and silicon after they are coated with a single layer ofgraphene。虽然石墨烯是令人难以置信的,但这些结果仍然令人惊讶,因为它是不可渗透的。利用这种能力石墨烯可用于保护材料免受氧化的,而不会影响它们与水相互作用的方式。

Rensselaer理工学院和赖斯大学的工程师发现石墨烯的极端薄度如何实现近乎完美的润湿透明度

石墨烯.is the thinnest material known to science. The nanomaterial is so thin, in fact, water often doesn’t even know it’s there.

Engineering researchers at Rensselaer Polytechnic Institute and Rice University coated pieces of gold, copper, and silicon with a single layer of graphene, and then placed a drop of water on the coated surfaces. Surprisingly, the layer of graphene proved to have virtually no impact on the manner in which water spreads on the surfaces.

Results of the study were published Sunday in the journal Nature Materials. The findings could help inform a new generation of graphene-based flexible electronic devices. Additionally, the research suggests a new type of heat pipe that uses graphene-coated copper to cool computer chips.

该发现源于Rensselaer教授Nikhil Koratkar和Rice教授Pulickel Ajayan领导的跨大学合作。

“We coated several different surfaces with graphene, and then put a drop of water on them to see what would happen. What we saw was a big surprise—nothing changed. The graphene was completely transparent to the water,” said Koratkar, a faculty member in the Department of Mechanical, Aerospace, and Nuclear Engineering and the Department of Materials Science and Engineering at Rensselaer. “The single layer of graphene was so thin that it did not significantly disrupt the non-bonding van der Waals forces that control the interaction of water with the solid surface. It’s an exciting discovery, and is another example of the unique and extraordinary characteristics of graphene.”

研究结果详述了“石墨烯的润湿透明度”中详述。在线看本文Nature Materials

基本上是石墨的孤立层,通常在我们的铅笔或我们烧伤烧烤的木炭中,石墨烯是单层碳原子,如纳米级鸡肉丝围栏。已知石墨烯具有优异的机械性能。该材料具有强大且强硬,因此其灵活性均可均匀地涂覆几乎任何表面。许多研究人员和技术领导者将石墨烯视为能够大大推进灵活,纸张薄设备和显示器的出现的能力。用作这种装置的涂层,石墨烯肯定会与水分接触。了解石墨烯与水分的相互作用是如何推动这项新研究的推动力。

The spreading of water on a solid surface is called wetting. Calculating wettability involves placing a drop of water on a surface, and then measuring the angle at which the droplet meets the surface. The droplet will ball up and have a high contact angle on a hydrophobic surface. Inversely, the droplet will spread out and have a low contact angle on a hydrophilic surface.

The contact angle of gold is about 77 degrees. Koratkar and Ajayan found that after coating a gold surface with a single layer of graphene, the contact angle became about 78 degrees. Similarly, the contact angle of silicon rose from roughly 32 degrees to roughly 33 degrees, and copper increased from around 85 degrees to around 86 degrees, after adding a layer of graphene.

这些结果让研究人员感到惊讶。石墨烯是不可渗透的,因为其连接的碳原子之间的微小空间对于水而太小,或者单个质子,或其他物质或以其他方式适应。因此,人们会期望水不会充当金,硅或铜,因为石墨烯涂层防止水直接接触这些表面。但研究结果清楚地展示了水如何能够感测底面的存在,并在那些表面上铺展,好像石墨烯根本不存在。

Water Molecules on Copper with 0, 1, 3, or 6 Layers of Graphene

As the researchers increased the number of layers of graphene, however, it became less transparent to the water and the contact angles jumped significantly. After adding six layers of graphene, the water no longer saw the gold, copper, or silicon and instead behaved as if it was sitting on graphite.

这种令人困惑的行为的原因是微妙的。水形成具有某些表面的化学或氢键,而水与其他表面的吸引力由名为van der WaaS力的非粘结相互作用决定。Koratkar表示,这些非粘合力与纳米级版的重力不同。类似于重力决定地球和太阳之间的相互作用,范德沃尔斯力决定了原子和分子之间的相互作用。

在金色,铜,硅等材料的情况下,表面和水滴之间的范德瓦尔斯力将水的吸引力决定在表面上,并规定了水的差距在固体表面上。通常,这些力具有至少几纳米的范围。由于长距离,这些力量不会被单一的存在破坏atom- 在表面和水之间的石墨烯层。换句话说,克拉特卡尔说,van der Waals力能够“通过”超薄石墨烯涂料。

If you continue to add additional layers of graphene, however, the van der Waals forces increasingly “see” the carbon coating on top of the material instead of the underlying surface material. After stacking six layers of graphene, the separation between the graphene and the surface is sufficiently large to ensure that the van der Waals forces can now no longer sense the presence of the underlying surface and instead only see the graphene coating. On surfaces where water forms hydrogen bonds with the surface, the wetting transparency effect described above does not hold because such chemical bonds cannot form through the graphene layer.

Along with conducting physical experiments, the researchers verified their findings with molecular dynamics modeling as well as classical theoretical modeling.

“我们发现van der Waals力量不会被石墨烯扰乱。Koratkar表示,这种效果是石墨烯的极端薄度的伪像 - 这仅是约0.3纳米,“Koratkar表示。“没有什么可以媲美石墨烯的薄弱。因此,石墨烯是用于润湿角度透明度的理想材料。“

“此外,石墨烯是强壮的,并且它不容易破裂或分开,”他说。“另外,使用化学气相沉积容易涂覆具有石墨烯的表面,并且相对简单地在大区域上沉积均匀和均匀的石墨烯涂层。最后,石墨烯是化学惰性的,这意味着石墨烯涂层不会氧化。没有单一材料系统可以提供石墨烯能提供的所有上述属性。“

A practical application of this new discovery is to coat copper surfaces used in dehumidifiers. Because of its exposure to water, copper in dehumidifier systems oxidizes, which in turn decreases its ability to transfer heat and makes the entire device less efficient. Coating the copper with graphene prevents oxidation, the researchers said, and the operation of the device is unaffected because graphene does not change the way water interacts with copper. This same concept may be applied to improve the ability of heat pipes to dissipate heat from computer chips, Koratkar said.

“It’s an interesting idea. The graphene doesn’t cause any significant change to the wettability of copper, and at the same time it passivates the copper surface and prevents it from oxidizing,” he said.

Along with Koratkar and Ajayan, co-authors of the paper are Yunfeng Shi, assistant professor in the Department of Materials Science and Engineering at Rensselaer; Rensselaer mechanical engineering graduate students Javad Rafiee, Abhay Thomas, and Fazel Yavari; Rensselaer physics graduate student Xi Mi; and Rice mechanical and materials engineering graduate student Hemtej Gullapalli.

该研究部分由先进的能源联盟(AEC)提供支持;国家科学基金会(NSF);和海军研究办公室(伊斯册)石墨烯多学科大学研究倡议(Muri)。

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