Chunwei Cheng

Raman Microscopy of Polymer Blends

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.

Raman and i.r. spectroscopy of electrochemically obtained conducting and non-conducting poly(N-vinylcarbazole)

Abstract The well resolved Raman spectra of electrochemically synthesized conducting and non-conducting poly( N -vinylcarbazole) were obtained. The Raman and i.r. spectra revealed that the conducting polymer had a 3,3′-dicarbazyl structure formed by dimerization at the 3,6 position and an appropriate mechanism was proposed. The conducting polymer was also obtained by electrolysis of the non-conducting polymer dissolved in dichloromethane. The conducting polymer obtained by this method was found to have a similar structure to that obtained by direct electrolysis of the monomer. The polymerization was monitored by the use of a specially designed cell, with in situ Raman spectra being taken from the electrode surface at different intervals. These spectra showed that there were no significant structural changes occurring in the conducting polymer during the polymerization process. In addition, the Raman image of the conducting polymer was taken by using the intense band which was located at 1600 cm −1 .