Porous silica antireflective coatings were prepared by incorporation of polyethylene glycol (PEG) in acid catalysed sols. PEG decomposed during curing, leaving pores in the films, resulting in a decrease in refractive index and an increase in transmission. Properties of the films were analysed by SEM, AFM, FTIR, ellipsometry and a scratch test. Very uniform porous films were obtained by adding PEG into sols that contain highly condensed silica particles. After curing at 400 deg C, films exhibited transmissions of up to 99.7%. Scratch resistance of these films is considerably better than that of coatings prepared from the conventional alkali catalysed and mixed catalysed sols with comparable refractive indices. A further improvement in scratch resistance was achieved without degradation in transmission by increasing curing temperature to 550 deg C.
