Nanoparticles doped PMMA films were prepared without surface treatment agent in order to investigate particle size and
concentration dependence of orientation-inhibition effect and photoelastic coefficient reduction. It is suggested that
nanoparticles with a diameter of less than about 30 nm exhibit orientation-inhibition effect. Photoelastic coefficient
reduction was independent of particle size and proportional to volume fraction. Doping nanoparticles has an insignificant
effect on degrading the transparency of polymers if the combination of nanoparticles and polymer matrix is appropriate.