Fascinating World of Atoms

Do you know what makes a gecko stick to the wall? Believe it or not, an extremely feeble force comes into play on tiny hairs of gecko's feet as soon as it touches the wall, keeping it stuck to the wall. This weak force - known as van der Waals' force - is just one sample of Nature's way of dealing with problems at the microscopic or nano level. 

"Acting at the nano level, van der Waals' force holds atoms and molecules together," said Prof. C. N. R. Rao, Linus Pauling Research Professor and honourary president of the Jawaharlal Nehru Centre for Advanced Scientific Research, Bangalore. Prof. Rao was delivering a special commemoratory lecture - 'Self Assembly as a Universal Phenomenon: The Prominent Role of Weak Interactions' - on December 11 at the Indian Association for the Cultivation of Science. 

Atoms and molecules, under the influence of van der Waals' force, assemble themselves one by one, carving out wonderful miniscule structures. In Rao's words, "Some of them make wheels while others go on to build ladders." 

"Imagine the minute structures formed by zeolites which work as molecular sieves," he said, adding, molecules of zinc phosphates show an array of different structures. In one dimension, a linear chain of zinc phosphate looks like a ladder, but when it is heated, a four-member monomer ring of the molecule regroups in a way that it reaches a higher dimension from zero dimension. 

"At the ground stage of self-assembly, atoms get together, building up cluster of atoms. Then, clustering of atoms makes molecules solid. Up to 100 nanometres (1nm=a billionth part of a millimitre), mind-boggling rules prevail. In the nano world, atomic clusters form, disobeying the nature of particles," Rao explained. 

From two to five nm, nano crystals reach 30-50 nm when they form giant clusters. In this entire range, physical laws governing the tiny world remain the same. This self-assembly is accomplished by van der Waals' force without the help of any external influence. Besides van der Waals' force, capillary force plays an active role in self-assembly of molecules. 

According to Rao, by exploiting the process of self-assembly, scientists could produce useful materials like polystyrene beads, carbon nanotubes and silver nanowire. "It has been found that in carbon nanotubes, carbon molecules have 100 times the strength of steel, yet they are only 1/60th of its weight," Rao said. 

Being good conductors of electricity, carbon nanotubes may have enormous applications in computers. "The marvelous feature of self-assembly can be seen up to a range of a few centimeters." 

The fascinating world of atoms and molecules, which build nano structures on their own heralds a future that will witness the diminishing role of strong force in manufacturing machines. "Instead, future machines will be built on the principle of self-assembly guided by weak interactions like van der Waals' force," concluded Rao.