Raman Microscopy of Polymer Blends

Abstract

The potential of Raman microscopy for the examination of phase structure and composition of polymer blends is described. Provided that highly efficient collection optics are used, together with a CCD camera detector, the common problems of specimen heating and fluorescence can be reduced by the use of a relatively low-power (25mW) HeNe laser. For thin (<5 μm) film specimens, submicron morphological features can be resolved and phase compositions determined. For thicker specimens, the sampling depth controls the spatial resolution, but micron-scale morphological features can be imaged. When the microscope is operated in the spectroscopic mode, the use of an intermediate slit permits essentially confocal operation and can reduce the sampling diameter to about one micron. In cases where the image is inadequate, such as for thick or highly scattering specimens, phase sizes may be estimated by collecting several spectra at random on the specimen surface and determining the apparent scatter in blend composition. When the phases are large in comparison to the sampling volume, the composition data will be highly scattered. When the phases are small, then all measured compositions should be close to the average. The technique is illustrated with the use of a rubber-toughened epoxy resin, a polyethylene-polypropylene blend, and a polyester (PET/PBT) blend.