The coated porous polyimide layers for optical scattering films

Abstract

We have investigated the optical scattering characteristic of the air-void micro-structure of air-voids of the porous polyimide (PI) layer prepared from a simple polyimide-precursor coating and the immersion precipitation method. For the careful control or tune of the generated pore-structure, the content of polar aprotic solvent in polar protic non-solvent bath was adjusted during the pore-generation process. To account the correlation between the generated micro-structure of a porous polymer layer and its optical scattering property, the optical haze values were calculated and compared with the measured total transmittance and diffuse transmittance values. And the calculated average optical haze value decreased from 0.88 to 0.53 as increasing the content of polar aprotic solvent in the coagulation bath. In addition, the light scattering mechanism was proposed for a prepared porous polymer film consisting of air-voids inside the polymer media and the rough surface at the ambient interface. Finally, for an analytical explanation, we also introduced Mie scattering and Scalar surface scattering which explains the light scattering inside pore structure as well as at the rough surface, respectively. Based on our systematic approach, it can be said that the net power of light scattering was the sum of Mie scattering and the surface scattering.