Start
Mar 28, 2013 - 17:00
End
Mar 28, 2013 - 18:00
Venue
Room 118 (Creativity Hall) Ground Floor Chemical Engineering Department
Event Type
Speaker
Apratim Chatterji (IISER-Pune)
Title
Self-assembly of ordered cylindrical nano-structures: A theoretical investigation of experimental results.
Abstract: We present a theoretical model which elucidates the physical principles involved in the formation of very uniform $CdS$ nanocylinders of different radii by combining the physics of flow diffusion self assembly and aggregation of constituent particles. Very recent experiments report that when $0.1$ M solutions of $CdCl_2$ and $Na_2 S$ were allowed to mix through some anodised alumunium oxide (AAO) nanochannels one observes the growth of an array of $CdS$ nano-cylinders on only one end of the AAO template [A. Varghese and S. Datta Phys. Rev. E . {\bf 85} 056104 (2012)]. These cylinders have a pore along the center of the cylinder but closed at one end. The reaction happens only in the $Na_2S$ chamber and growth of cylinders of uniform size and shape continues as long as the supply of the reactant molecules ($CdCl_2$ and $Na_2S$ ) is maintained. To try to understand the physics of the observed phenomenon we propose a model mechanism where the $Cd^{+2}$ ions exit the AAO-nanochannel to enter $Na_2 S$ chamber with a finite velocity these ions then react with the diffusing $S^{-2}$ ions to form $CdS$ which then self assemble to form cylinders of uniform width and cross-section. The flow of $Cd^{+2}$ out of the AAO nano-channel is the key symmetry breaking feature which fecilitates formation of uniform cylindrical structures of $CdS$ instead of a $CdS$ precipitate. Since our model does not crucially depend on the chemical details of the reaction this mechanism can be extended to self-assemble other structures of relevance.