Study of organic phase mobility in nanocomposite organic-inorganic coatings

摘要

Organic-inorganic hybrids synthesized by a dual photopolymerization and condensation process from (i) two organic precursors, either poly(ethylene glycol) alpha,omega diacrylate ((M) over bar (w) = 600) (PEGDA) or bisphenol-A-ethoxylate(15EO/ phenol)-dimethacrylate (BEMA), (ii) the organic-inorganic bridging monomer (methacryloyl-oxypropyl-trimethoxysilane, (MEMO)) and (iii) the inorganic precursor tetraethoxysilane (TEOS) were investigated by differential scanning calorimetry (DSC) and dynamic mechanical spectroscopy (DMTA). It is found that progressive formation of the crosslinked network during the different steps of hybrid production results in changes of molecular mobility that show up in changes of the glass transition of the organic phase. While moving from the organic precursor to the final hybrid through the subsequent photopolymerization and condensation reactions, the transition is seen to broaden, decrease in intensity and shift to higher temperature. Excellent agreement of DSC and DMTA results is obtained. Dynamic mechanical analysis of the hybrids coated on PET film (coating thickness 10 and 40 mu m) show an additional up-shift of T-g, more marked in the case of the thinner hybrid coating. This result is attributed to molecular interactions at the substrate-coating interface that locally hinder molecular mobility. The consequent increase of T-g is more evident when the coating layer is thin. The results show the potential of the DMTA technique in coating-polymer substrate adhesion studies. Finally, the relaxation spectrum of the hybrids is sensitive to humidity absorbed from the environment and reversibly changes in absorption-desorption cycles.