Water Friction in Two-Dimensional Crystal Nanofluid Channels

The speed of water flow is a limiting factor in many membrane-based industrial processes, including seawater desalination, molecular separation, and osmotic power generation.

Researchers at the National Graphene Institute (NGI) at the University of Manchester published a study in Nature Communications showing that friction is significantly reduced when water passes through nanoscale capillaries made of graphene, while hexagonal boron nitride (hBN) has a surface morphology and crystal structure similar to graphene and has high friction properties.

The team also demonstrated that the speed of water can be selectively controlled by covering high-friction hBN channels with graphene, thereby greatly improving the penetration and efficiency of so-called "smart membranes".

Rapid and selective fluid flow is common in nature—for example, in a protein structure called aquaporin that transports water between animal and plant cells. However, the precise mechanism of the rapid flow of water in the atomic plane is not fully understood.

Studies by the Manchester group, led by Professor Radha Boya, have shown that—contrary to the general belief that all hydrophobic atomic planes should provide little friction to water flow—in fact, friction is mainly controlled by electrostatic interactions between flowing molecules and their closed surfaces.

Dr. Ashok Keerthi, lead author of the study, said: "Although hBN has similar water 'wettability' to graphene and molybdenum disulfide, to our surprise, the flow of water is completely different. Interestingly, the rough graphene surface has only a few yards deep indentation/terrace, or the atomically corrugated MoS2 surface, which does not hinder the flow of water in the nanochannel."

Thus, atomically smooth surfaces are not the only reason for the frictionless water flow on graphene. In contrast, the interaction between flowing water molecules and two-dimensional materials plays a crucial role in transferring the friction of fluids within nanochannels.

Professor Boya said: "We have demonstrated that nanochannels covered with graphene at the outlet show enhanced water flow. This is very useful for increasing the water flux of the membrane, especially in processes involving evaporation, such as distillation or thermal desalination."

Understanding the friction and interaction of liquids with pore materials is essential for the development of efficient membranes for applications such as energy storage and seawater desalination.

This latest study adds to the increasingly influential work of NGI researchers, and the University of Manchester strengthens its frontier in nanofluid research to improve industrial applications in sectors such as wastewater treatment, pharmaceutical production, and food and beverages.

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Matexcel is a leading service provider in materials science, with years of commitment to supply better polymers, nanoparticles and other materials for worldwide customers from both academia and industry.