It turns out that 'water' is also compressed in the nanoscale world and its volume may be small

In general, water can hardly be compressed and it is said that no matter how much force is applied, its volume hardly changes. Using the characteristics, machinery that uses hydraulic pressure works around society, but it turned out that such common sense is overturned in a special environment. Studies have revealed that water may be compressed in an atomic level world where potential gradients exist in two regions.

Phys. Rev. Lett. 120, 268101 (2018) - Water-Compression Gating of Nanopore Transport
https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.120.268101

Water compresses under a high gradient electric field
https://phys.org/news/2018-07-compresses-high-gradient-electric-field.html

The result of this research was announced by the research team of the University of Illinois at Urbana-Champaign . Professor Alexei Akimentev of physics and James Wilson of a postdoctoral researcher said that a fine hole "nanopore" in a sheet-like substance " graphene " having only one carbon atom as shown in the following figure (Nanopore) "was opened and water molecules trying to pass through the hole were compressed by 3% at the maximum when the potential difference" potential gradient "was present on both sides of the graphene.

By AlexanderAlUS

The research team found this phenomenon in a study to test a new method of DNA sequencing technology using nanopores of graphene. In recent years, this field is expected as a technology that enables inexpensive DNA sequencing than in the past, and research is under way around the world. The mechanism is to move graphene with nanopores into water and create a potential difference on both sides of the membrane to move water, DNA and ions by the potential difference. At this time, DNA can be identified by reading the flow of ions caused by the four bases of DNA.

With this technology, the size of nanopores becomes a very important factor. As mentioned earlier, graphene has only a thickness of one carbon atom, the nanopore diameter is only 3 nanometers, and it is only about 10 carbon atoms in size. A DNA molecule about 2 nanometers in diameter passes through this hole.

DNA passes through graphene nanopore - YouTube


Professor Akimentev and Mr. Wilson aimed at realizing controlling the speed of DNA molecules through nanopores by computer simulating this movement.

From the previous experiments, it was known that increasing the applied charge increases the migration speed of DNA molecules, but if the charge is increased by 10 times its movement stops and the DNA molecule can pass through the nanopore I knew it would disappear. Professor Akimentif and others who studied the cause, said that "the water is compressed by the gradient of electric potential" has come to the conclusion.

Professor Akimentef said, "We found that the gradient of potential compresses water because water is a dielectric because this phenomenon is not caused by a very high electric field, It is caused by the state that there is a gradient in the electric potential between the space and the space The electric charge given to the water molecule is aligned along the electric field and the electric charge near the place where the electric field is the highest is from the place with the weakest electric field It will be pulled strongly. "

"The turns out the gradient of the electric field is what is the electric field will not do this, only a field that changes over space. electric field, and the charges that are nearer where the electric field is highest are pulled harder than the charges nearer where the electric field is weakest.

The compression ratio of water at this time is only 3%, but this has the same compressibility as water under the condition of 100 atm. Professor Akimenti and others have concluded that this highly compressed water creates the condition "DNA molecule can not pass" as described above. In the following computer simulation video by Professor Akimentef et al., The state that compressed water "pushes back" the DNA molecule is reproduced.

Water compression blocks DNA - YouTube


Although it became clear that water can be compressed in the research of DNA sequencing technology using nanopores of graphene, professor Akimentev said that this technology can be applied to living cells having a very similar molecular structure We believe that it can be applied to the identification and separation of chemical substances.