Refractive index of corona-treated polypropylene films

The samples under investigation are 20??m thick isotactic polypropylene films corona treated at different corona polarities and grid voltages in a three-electrode system. In order to control the results of the applied treatment a combination of two refractive index (RI) measuring techniques (laser refractometry and spectrophotometry) is used to study RI dispersion in the spectral range 400?1000?nm. It is found that the surface RI was lower than the volume RI. After a corona treatment both surface and volume RI increase. The changes of the volume RI as compared to surface values are more influenced by the corona treatment conditions: the greater the grid potential, the bigger the volume RI.