Microsphere Pattern Prepared by a “Reverse” Breath Figure Method

Abstract

We have reported an interesting method, named reverse breath figure, for the preparation of polymeric microsphere patterns. By the same procedure as breath figure, instead of under a humid atmosphere, linear and star-shaped poly(styrene-block-butadiene) copolymers dissolved in solvents such as toluene, trichloroform, and dichloromethane were cast onto the surface of a glass substrate in methanol or ethanol vapor. After the complete evaporation of the solvent, microspheres with the diameters ranging from hundreds of nanometers to several micrometers were prepared. The microsphere patterns are the reverse of the honeycomb porous structure of breath figure. The mechanism of the microsphere formation has been studied to show that when the surface tension of the polymer solution is 1.5 mN/m higher than that of the condensed liquid, microsphere patterns can be prepared, whereas a honeycomb porous film of breath figure can be obtained when the surface tension of the polymer solution is lower than that of the condensed liquid. The viscosity of the polymer solution is also an important factor to influence the fabrication of the microsphere patterns.