Polariscopic imaging and vibrational characterization of hybrid films for packaging

Polymeric films (low-d. polyethylene and oriented polypropylene) for packaging applications coated with org.-inorg. nanocomposite hybrids have been prepd. by sol-gel process. Tetraethoxysilane and two different org. phases, polyvinyl alc. 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 IR and Raman spectroscopies. Through a new polariscopic imaging technique, the bi-dimensional maps of the optical anisotropy of the samples, both as-prepd. and under mech. 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 alc. sample.