Characterization of a polyethylene–polyamide multilayer film using nanoscale infrared spectroscopy and imaging

Atomic force microscopy (AFM) and infrared (IR) spectroscopy have been combined in a single instrument (AFM-IR) capable of producing IR spectra and absorption images at sub-micrometer spatial resolution. This new device enables cross sections of multilayer films to be spectroscopically characterized at levels not previously possible. In particular, it was possible to observe nanoscale IR spectroscopic differences, as well as thermal and mechanical property differences, in the tie layers located between the individual polyethylene and polyamide layers of a multilayer cling film of initially unknown structure. It also appears that a two-μm-thick barrier layer between two polyamide layers near the center of the multilayer cling film consists of an ethylene-vinyl alcohol copolymer. Mechanical stiffness and thermal property differences are also observed between the various layers in the film. This powerful capability should prove generally useful for reverse engineering complex unknown multilayer film materials, as well as in aiding the intelligent design and coextrusion of superior multilayer film materials.