Making the surface switch
17 Jan 2003
A team of researchers at the University of California at Santa Barbara and colleagues from MIT and UC Berkeley has designed and demonstrated a reversible 'surface switch'.
The 'switch' was developed using several alkanethiol molecules - linear chains of several carbon atoms that protrude like porcupine quills from the surface of a gold wafer. Most of the chain is hydrophobic (averse to water), but the topmost part (a carboxyl group [CO2H]) is hydrophilic (attracted to water).
When an electrical field is applied to the gold wafer, it causes the negatively charged carboxyl heads to be attracted to the positively charged surface, so that the chains bend over towards the gold wafer base, thereby exposing the hydrophobic middle of the chain. The surface has hence switched from hydrophilic to hydrophobic and can readily be switched back with the removal of the electric field.
Although the reported experiments demonstrate the principle of reversible switching between hydrophilic and hydrophobic properties, other properties can be 'switched' depending on the desired application, the researchers say.
The researchers also believe that their findings may, with further study, have implications in dynamic regulation of macroscopic properties, such as wettability, adhesion, friction or biocompatibility.
Potential applications might include microfluidics, microengineering of smart templates for bioseparation or data storage, or microfabrication of controlled-release devices.
