Rings Made of Little Rods
Water droplets as templates: gold nanorods self-assemble into rings
Nanoscale objects organized into superstructures are interesting because the properties of such tiny particles depend not only on their composition, shape, and size, but also to a large extent on their spatial distribution and the degree of their ordering within a superstructure.
Bishnu P. Khanal and Eugene R. Zubarev coated gold nanorods with polystyrene. The tiny polymer chains in the coating stick out from the rodlike bristles. Their function is to make the rods soluble in organic solvents but insoluble in water - which is important for the self-assembly process. The nanorods are dissolved in dichloromethane, and then a carbon-coated grid is dipped into this solution. When the grid is pulled out, a thin layer of solution clings to it. The highly volatile dichloromethane quickly evaporates into the air, which intensely cools the surface of the liquid film. As a consequence, humidity from the air condenses onto the surface. Because water and dichloromethane are immiscible, the condensation forms tiny droplets of water. When the dichloromethane has largely evaporated, the last remnants of the solution form rings around the water drops. Once the dichloromethane has completely evaporated, the substrate warms back up to room temperature and the water droplets also begin to evaporate. This leaves behind ring-shaped structures made of nanorods. Images obtained with an electron microscope show that the nanorods in the rings are oriented randomly when their concentration in the original solution is high. However, at lower concentrations the result is truly amazing: The nanorods are oriented in a head-to-tail sequence along the edge of the ring.
Original publication: Eugene R. Zubarev et al.; "Rings of Nanorods"; Angewandte Chemie International Edition 2007, 46, No. 13, 2195-2198.
Most read news
Topics
Organizations
Other news from the department science
Get the analytics and lab tech industry in your inbox
From now on, don't miss a thing: Our newsletter for analytics and lab technology brings you up to date every Tuesday. The latest industry news, product highlights and innovations - compact and easy to understand in your inbox. Researched by us so you don't have to.