Mar 17, 2009
Locking nanoparticle prevents gas leakage
Scientists in Russia are using molecular dynamics to model the behavior of a lock and fill nanocapsule. The closed-cage design could offer a safe and effective way of storing gases such as methane under normal conditions.
The structure consists of a series of combined nanotubes with diameters (20, 20), (10, 10) and (8, 8) that contain a positively charged endohedral complex (K@C60), which can be displaced by the application of an electric field to lock and unlock the device.
The nanocapsule's operation can be divided into several steps: adsorption, storage and desorption. During the adsorption step, the endohedral complex K@C60 is located near the base of the nanocapsule. The molecules of methane penetrate through the hole in the nanocapsule and are adsorbed on its walls. To pass to the storage step, it is necessary to close the nanocapsule's outlet opening. The K@C60 is displaced to the outlet opening under the action of the electric field and blocks it, so that the methane molecules cannot leave the nanocapsule.
When the K@C60 reaches the nanocapsule region (8, 8), the locking particle stops because it cannot move any further as the inner space of the region (8, 8) is smaller than the volume of the K@C60. Due to the methane pressure and the action of capillary forces, even after the disappearance of the electric field the K@C60 remains in its locking position.
Now the methane storage step can begin. At this step, the external thermodynamic conditions are returned to normal. As a result of the methane expansion inside the nanocapsule, the K@C60 is pressed to the beginning portion of the region (8, 8). The K@C60 hinders the escape of the methane molecules from the nanocapsules because the distance between the nanotube walls and the endohedral complex is insufficient for the gas to penetrate between them.
During the desorption stage, the K@C60 moves back to the base of the nanocapsule under the action of the electric field. Because of the excess pressure inside the nanocapsule, the methane molecules leave the inner space. A considerable portion of methane remains inside the nanocapsule and the concentration of the methane molecules is observed in the regions of the nanotubes (10, 10) and (8, 8).
For complete removal of the methane by the electric field, the K@C60 displaces toward the region (10, 10) and squeezes the methane out. After that the K@C60 returns to the nanocapsule base. The methane molecules concentrate in the region (10, 10) and the K@C60 squeezes them out again. This takes place until all of the methane molecules have left the inner space of the nanocapsule.
Thus, the nanocapsule presents a rather complex structure, in which the locking element K@C60 is controlled by an external electric field. Only the direction and electric field intensity value determine the K@C60 position in the nanocapsule and, correspondingly, the phases of adsorption, storage and desorption of methane.
About the author
Prof. Alexander V Vakhrushev and Dr Mikhail Suyetin are based at the Applied Mechanics Institute, Ural Division of the Russian Academy of Sciences, Izhevsk, Russia. They are conducting theoretical investigations into new forms of nanocapsules for effective and safe storing of gases. Prof. A V Vakhrushev's team is interested in the formation of nanoparticles, their movement and their self-organization in nanosystems.