Raman Microscopy for the Examination of Polymer Laminates
Raman microscopes are manufactured for both dispersive and FT-Raman systems. A natural extension of the Raman technique, the laser beam is focused to provide sample illumination on the micron scale and Raman scattering is collected with the instrument hardware to produce spectra of samples with a spatial resolution approaching 1-10 mm. Mapping of a sample surface is accomplished by examination of discrete sample sites and collection of multiple Raman spectra. Mapping of sample surfaces can provide structural data on a microscopic scale. The variety of Raman microscope designs and microscopic methods provide the ability to routinely utilize imaging and microscopy for the investigation of polymer surface structure, or the defect and contaminant analysis of coatings, polymer films and laminates.
The continued improvements in lasers, monochromators and detectors are reducing the complexity and cost of Raman instruments while broadening the application of Raman spectroscopy for analytical applications. Oxygen barrier coatings for food and pharmaceutical packaging were analyzed using Raman microspectroscopy.3 The Raman microscope has also been used to study the selective surface modifications on PVC films4 and tungsten/poly(ethylene glycol) films.5 Microspectroscopy has also been used to identify impurities in laminates such as the identification of oil contaminants in the polymer coating of beverage cans.6 Numerous examples of the use of Raman spectroscopy to examine the structure of polymers are present in the literature, and most of these include the vibrational assignment of the peaks in the Raman spectrum.7,8