Preparation and characterization of surfactant-induced nanoporous PMMA film

Porous polymer films were prepared by spin-coating of PMMA solutions that contained surfactant (sodium dodecylbenzenesulfonate, NaDDBS) at concentrations higher than the critical micelle concentration, and by selectively removing the water-soluble surfactant molecule in distilled water. After removal of NaDDBS, the nanoporous structure was confined by FE-SEM. The resulting pore size was found to be much smaller than the wavelength of the visible light, and therefore, the nanoporous thin films were optically homogeneous. However, when the film was prepared with 30 wt% porogen loading, the resulting porous film became quite opaque and the refractive index could not be measured. The size and the total volume of the pores in the PMMA film increased with the increase in the porogen concentration. Upon increasing the amount of the surfactant in the film, the refractive index of the nanoporous PMMA film changed from 1.493 to 1.483. The refractive index of the nanoporous polymer film was found to be inversely proportional to the porogen concentration and the pore volume. Transparent PMMA films containing nanoscale pores randomly distributed throughout the film thickness are expected to be versatile in optical applications such as the optical waveguide.