Multi- Length Scale Porous Polymers

Thin films with porosities spanning from the nanoscopic to the macroscopic are obtained by combining breath figures (BFs), micrometer-sized surface cavities arising from the condensation of water on the surface of a film as solvent evaporates rapidly, with the nanoscopic morphology inherent to block copolymers. Using chloroform as a solvent for polystyrene-b-poly methyl methacrylate (PS-b-PMMA) block copolymers (BCPs), micrometer-sized pores arise from the formation of the BFs, while nanoscopic pores are generated by the removal of the PMMA by deep UV-irradiation, which also crosslinks the PS. Solvent retention, though, limits its utility. This is overcome using PS-b-poly(n-butyl methacrylate) dissolved in dichloromethane where, again, multi-length scales of porosity are achieved by a selective removal of one component of BCPs. Arrays of nanopores on the surface of a film can also be obtained by swelling the hydrophilic component block of PS-b-poly(ethyleneoxide) (PEO) with water vapor, under controlled humidity. Simultaneously, large pores can be obtained by macrophase separation between BCPs and water, which leads to multi-length scale porous films.