Caltech Researchers Find Answer In Entropy For Long Standing Nanotube Mystery

Everyone is always bewildered at the thought when scientists talk of nanotechnology and its ever expanding uses. It has however remained a 'riddle'-still unsolved as to why water tries to flow inside the nanotubes.  Finally researching upon this topic, scientists at the University of California, have #-Link-Snipped-# or the disorder in a system which leads to chaos.

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A cut section of 2.0 nanometer-diameter carbon nanotube, revealing confined water molecules. Image Credit: Caltech.

Water is made up of strong covalent bonds which make the structure of water stable. These strong bonds formed by water require a high energy to be broken. However if this is done, water molecules have a tendency to move in to the annular space in these nanorods to compensate for this energy loss with the entropy. Caltech scientists William Goddard, Tod Pascal along with Yousung Jung of the Korea Advanced Institute of Science and Technology (KAIST) have presented their work titled #-Link-Snipped-# in July 19 edition of proceedings of the national academy of sciences.

In normal physical terms, Entropy stands for the measurement of disorder in a system. In thermodynamics it is the relation between energy lost by the system to the temperature change in the system represented by S where S=dQ/dT. Adopting a mathematical approach, William Goddard who is the Charles and Mary Ferkel Professor of Chemistry, Materials Science, and Applied Physics at Caltech and director of the Materials and Process Simulation Center have tried to focus their attention on the calculation of entropy of the individual water molecules.  They were successful in doing so. So much so that the group found that they did all these calculation in just 36 hours that other research did in 8 years!

In doing so, the researchers have classified in to three groups according to their diameter sizes. The first one and the smallest one has a diameter ranging from 0.8 and 1.0 nanometers. The behavior of water molecules was a bit peculiar in them. While an average water molecule has a limited degree of freedom, the one which enter in the smallest nanotubes live in nearly gaseous state enjoying a higher degree of freedom but also with higher entropy in almost a single line.

The next size ranges from the diameters 1.1 to 1.2 nanometers thick. Water dwells in it something similar to Ice Crystals. However this time it is not on account of Entropy, rather it is because of the crystal bonding interactions which make it favorable for water molecules to escape out into them out of the closely networked mesh. The third and the last one is the major chunk of nanorods ranging from 1.4 to 2.7 nanometers in which the water is found to behave as a liquid. In all the three ranges the molecules exhibit a greater degree of freedom than seen normally.

To calculate these results in merely 36 hours, Goddard and his post doctoral colleague Tod Pascal had formulated method using a super computer. The research will be particularly useful in developing a water purification system thereby widening the scope of nanotechnology. This would also prove to be effective given that the process occurs at a nano level, minute impurities can be eliminated from the basic building block of life. Today it is only water, a further research in this regard can expand this technology to other fluids may be “oil based” in future.