Formation of nanodents by deposition of nanodroplets at the polymer-liquid interface

Recent work has shown that it is easy to form nanoscale droplets of fluid phase at interfaces. Here we demonstrate the use of these small droplets as templates for facile modification of a polymer surface. Small dents with the depth of less than 20 nm were created at the interface between polystyrene and water by the deposition of toluene droplets. Polystyrene is much more soluble in the toluene than in the water, so modification of the polystyrene occurs within the droplet but not under the water. The modification is seen to be permanent because the surface pattern remains on the polystyrene after removal from the liquids. Two mechanisms for surface modification are discussed: plastic deformation of the polystyrene due to interfacial tension and transport of dissolved polystyrene to the three-phase line during dissolution of the droplet (the coffee stain effect).