Formation of self-assembled microstructure on the polymer surface

Abstract

Breath figure is a self-assembly method to prepare hexagonally ordered porous structure with the pore size in the range of sub-micron to several microns from evaporating polymeric solution under the humid atmosphere. It employs solvent evaporation to cool the surface of solution which triggers water condensation. In the proper condition, polymer and organic solvent can effectively reduce the coalescence rate of condensed water droplets and form a self-assembled hexagonal structure after solidification of the polymer.

A new development in breath figure method is performed to prepare the ordered porous structure from a ternary solution of polystyrene/chloroform/short-chain alcohols. Short-chain alcohols participate in the stabilization of water droplets and will evaporate after complete drying. Due to the effect of short-chain alcohols, polystyrene which is a hydrophobic polymer with a weak stabilization ability can produce a porous structure in a wide range of casting conditions. The highest ordered structure is gained when shortest alcohol (methanol) is used in the ternary solution.

In application part, the microlens arrays are produced by replica molding of PDMS from ordered porous template. The optical properties of the microlens are characterized by the image formation and focal length measurements. The wettability characterization of flat polymer and porous polymer are performed with contact angle analysis and theoretical calculations.