Polariscopic imaging and vibrational characterization of hybrid films for packaging.

Polymeric films (low-density polyethylene and oriented polypropylene) for packaging applications coated with organic-inorganic nanocomposite hybrids have been prepared by sol-gel process. Tetraethoxysilane and two different organic phases, polyvinyl alcohol and a diblock copolymer polyethylene-polyethylene glycol were used as precursors. Information about the hydrolysis and polycondensation degrees was obtained by investigating the vibrational features of the coatings by means of attenuated total reflectance-Fourier transform infrared and Raman spectroscopies. Through a new polariscopic imaging technique, the bi-dimensional maps of the optical anisotropy of the samples, both as-prepared and under mechanical strain, were obtained. The maps showed inhomogeneous retardation and nearly flat azimuth distributions. The anisotropy properties of the samples depended mainly on the substrates and were not influenced by the coatings, while the optical transmission was slightly better for the tetraethoxysilane-polyvinyl alcohol sample.