Published online by Cambridge University Press: 31 January 2011
The synthesis of single crystalline rectangular silver bar using polyacrylamide (PAM) and silver nitrate (AgNO3) by a hydrothermal process is reported. PAM has been used to create a reducing atmosphere as well as nucleation sites to produce silver seeds along the PAM chain. Several silver nanostructures viz. nanoparticles, growth of silver nanowires, and finally a single crystalline silver nanobar with a square cross section and of several microns in length, depending upon maturity and temperature of the hydrosol, are synthesized. At relatively lower temperatures (above 380 K) and higher pressure amide group of PAM is hydrolyzed with the liberation of ammonia (NH3), which produces a reducing atmosphere. As a result, the degraded PAM chain acts as nucleation sites to produce the assembly of silver nanocrystals along the chain. As the hydrosol becomes more and more mature, a directional growth of silver nanocrystals, called a mesocrystal, is formed. This mesocrystal is converted into single crystals due to fusion of higher energy surfaces (100) of nanocrystals to minimize the total surface energy. This growth process is completed with the formation of a single crystalline rectangular silver bar with a square cross section due to the growth of silver along the [110] direction.