“This is a result of what is known as coordination-driven self-assembly,” explained associate professor Niveen Khashab. “The metal ions interact with different chemical motifs leading to the formation of novel frameworks and morphologies.”
The usual top-down approach involves the etching away of material to leave the desired sculpted structure behind. Because this approach can be tricky, expensive and time consuming, KAUST researchers became motivated to find a new approach.
The team demonstrated this bottom-up approach in the self-assembly of microscale toroids made of both inorganic and organic materials.
The toroids created by the team were formed via metal coordination. A metallic sodium chloride atom, an amphiphilic molecule called saponin and a polymer known as chitosan were combined and formed weak chemical bonds.
According to the researchers, coordination bonding between the iron atoms and the oxygen and the hydrogen in the molecules drove the self-assembly of star-like nanostructures within just a few minutes. Repulsive electrostatic and hydrophobic interactions then lead to the formation of toroids.
“Next, we hope to prepare a new generation of these hybrid structures with a temperature-responsive gap size,” said Khashab. “These toroid structures could be used as pockets for active catalysis and separation.”
