Measurements of concentration profiles in polymeric solvent coatings by means of an inverse confocal micro Raman spectrometer - Initial results

Concerning quality and drying time of a process the key issue is the progression of the concentration profiles within the film during drying. This contribution reports on the development of a new measuring technique, an Inverse-Confocal-Micro-Raman-Spectrometer, for online measurements of concentration profiles during drying in thin (5-200 mum) polymeric solvent coatings. The spatial and temporal resolution of the measurements is up to one micron and one second. A calibration method has been developed by taking Raman spectra of different, precisely concentrated samples in sealed quartz glass cells and by calculating the ratio of the intensities of the characteristic Raman peaks. The accuracy of this basic calibration method is very good over a wide concentration range. Initial investigations were carried out on the polymer solvent systems: polyvinyl acetate(PVAc)-toluene, PVAc methanol, PVAc-benzene, and PVAe-methanol-toluene, PVAc-methanol-benzene.