Bored of bath-cleaning? Wearied by window-washing? Thanks to a group of scientists in Israel these mundane chores could soon be consigned to the past.
Itamar Willner and colleagues at the Hebrew University of Jerusalem have made a quinine-coated 'smart surface' whose wettability can be switched using either an electrical or a chemical trigger. Such surfaces are inspired by self-cleaning systems in nature. The lotus leaf, for example, has a hydrophobic surface which allows water droplets to roll off the leaf, removing dirt from its surface.
Willner and his team coated a gold surface with hydrophobic benzoquinone, which is reduced to hydrophilic hydroquinone using either an applied voltage or a chemical reducing agent. Hydroquinone has two hydroxyl groups that interact strongly with the water, causing the surface to become 'wetter' when reduced.
"A smart idea to create a smart surface"
- Jilie Kong, Fudan University, Shanghai
'The hydroquinone/benzoquinone surface evolved from a much more complex system that, after a lot of effort, did not work at all. We were still surprised with how robust the [simple] system [was] and how dramatic the changes were that we observed,' said Willner.
The team's smart surface is easily prepared and the small size of quinone means that a lot of molecules can be packed into the surface, causing large macroscopic changes in the surface wettability.
Aside from self-cleaning applications, these clever surfaces may be used in microfluidic devices that could provide new analytical procedures for clinical diagnostics. For example, if the inner part of a capillary was coated with a conductive film functionalized with Willner's quinine monolayer it could be used to suck minute volumes of fluid from cells or organs.
'A smart idea to create a smart surface,' said Jilie Kong, an microfluidics expert at Fudan University, Shanghai. 'The reversible change of hydrophobicity/hydrophilicity is promising in the design of novel microfluidic chips or biosensors,' said Kong.