Fluid imaging

A new optical imaging technique shows how fluids are affected by nanopatterned surfaces

Credit: © 2008 NPG

Surfaces inscribed with nanoscale patterns can be used to manipulate certain fluids, such as liquid crystals, on a very small scale. Now Charles Rosenblatt at Case Western Reserve University in Cleveland and co-workers¹ have acquired the first images showing exactly how such fluid molecules are affected.

Their imaging technique, called optical nanotomography, uses an optic fibre to deliver polarized laser light into the fluid. By scanning the tip back and forth at different heights and collecting the transmitted light, it builds up a 3D dataset on the orientation of fluid molecules.

To test this method, the researchers inscribed a pattern of tiny zigzag grooves into a polymer substrate using an atomic force microscope tip. The substrate was covered with a nematic liquid crystal, which generally has all its molecules pointing in one direction. The optical nanotomography revealed that the liquid-crystal molecules near the substrate aligned themselves with the zigzag grooves, while those further up remained in a straight configuration, as predicted by theory.

The study shows that optical nanotomography can provide higher near-surface resolution than other imaging techniques. It could find applications in observing and manipulating other liquid-crystal-like systems consisting of DNA, viruses or carbon nanotubes.