Results reported in the May 24, 2017 issue of Phys.org is titled: “Water is surprisingly ordered on the nanoscale.” (Reference is at the end of the blog.) “Researchers from AMOLF and Swiss EPFL have shown that the surface of minuscule water drops surrounded by a hydrophobic substance such as oil is surprisingly ordered. At room temperature, the surface water molecules of these droplets have much stronger interactions than at a normal water surface. This may shed new light on a variety of atmospheric, biological and even geological processes.”
The article indicates that the researchers have developed an ultraviolet laser with overlapping, very short pulse duration, which enabled them to measure water droplets in the region of 25nm to 50nm. The purpose of this work was to develop an understanding of the interaction these size droplets have in interacting with other particles. Water droplets this size occur naturally in the atmosphere. Specific investigations were looking at the reaction in a hydrophobic environment.
The resulting findings indicate that the surface of the water is more organized than expected. There is a very hydrogen bond that appears in supercooled liquid at least 50 degrees higher than anticipated. Researcher Sylvie Roke commented: “The chemical properties of these drops depend on how the water molecules are organized on the surface, so it’s really important to understand what’s going on there.” Future work will target the water surface with different materials including salt.
For me the interesting part of the work is that it is examining liquid molecules and not solid material. If one examines the work that has been done on material like iron or aluminum, there exists a more reactive material when the particle size get slightly smaller than 50nm. Why? The reason is that the number of atoms on the surface and able to react with external forces is a significant portion of the total atoms. A very rough rule-of-thumb that I use is at 50nm about 3% of the atoms can be influenced by the surface interactions. At 3nm, roughly 50% of the atoms can be influenced by surface interactions. Somewhere between these two extremes, there is sufficient interaction to cause a change in atomic and molecular behavior.
The fact that the researchers can observe results on nano-sized liquids is very promising. Work has been ongoing on solids for years and we are still learning about how the surface interactions influence the reactions. Being able to move into the liquid realm should provide for some interesting and unexpected results.
Remember that the material properties continue to change as the size gets smaller. The pictures of different size gold particles in solution with each exhibiting different colors is just one example of changing properties. Imagine what will be found if different sized molecules of the same molecules can be individually examined. This work could be the first steps in an interesting and promising new field of research.
References: https://phys.org/news/2017-05-surprisingly-nanoscale.html
