Characteristics of novel transparent poly(methyl methacrylate)/silica nanoparticle hybrid film prepared based on entanglement-agglomeration transition mechanism

Abstract

Using polydisperse poly(methyl methacrylate) (PMMA) and SiO2 nanoparticles with an average particle diameter of ~15 nm, transparent PMMA/SiO2 hybrid films could be fabricated based on the agglomeration mechanism of nanoparticles in the suspension. The calculated distance between the particles in the transparent films was ~30 nm, corresponding to the actual measured value of 31 nm obtained from the small-angle X-ray scattering intensity. Upon heating the transparent hybrid films to 140 °C, above the glass-transition temperature of PMMA, the transmittance of UV light decreased significantly with the heating time for hybrid films with Mw=9.6 × 104 and a critical molecular weight (Mc) of 3 × 104 or greater, at which PMMA chains show effective entanglement. However, for hybrid films with Mw=0.3 × 104 and with the Mc or a lower molecular weight, the initial high transmittance was sustained over the entire wavelength range even after a long period of heating, and no agglomeration of the SiO2 nanoparticles was observed. Such molecular weight dependence was also observed for monodisperse PMMA/SiO2 hybrid films, leading to an examination of the difference in the rates of polymer chain entanglement and disentanglement. The critical molecular weight (Mc), at which the entanglement effect of the PMMA chain occurs is ~3 × 104. When the PMMA molecular weight in the hybrid suspension and film is such that Mc < Mw, such formation of molecular chain entanglements acts as a driving force for the agglomeration of SiO2 particles. In cases in which the PMMA molecular weight in the hybrid suspension and film is such that Mw< Mc, because no effective entanglements are formed, there is no driving force for the agglomeration of the SiO2 nanoparticles.