Lateral mapping of poly(styrene-co-maleimide) nanoparticle coatings on paper by confocal Raman microscopy

Fourier transform Raman spectroscopy and (dispersive) confocal Raman microscopy have been applied to quantitatively and qualitatively describe the local distribution of chemical moieties of poly(styrene-co-maleimide) coatings on paper substrates containing different amount of imide. In parallel, local coating defects have been imaged for a better understanding of the influence of the coating composition on homogeneity at macro- to microscale levels. From FT-Raman spectroscopy, the imide content was calculated in quantitative agreement with previous thermoanalytical data. From dispersive spectroscopy, the measuring parameters were optimized for single-point measurements including signals of the coating and macropoint measurements including more intense signals of the paper. The large surface maps (5 × 5 mm2) provided good quantification for the lateral distribution of imide moieties and coverage for coatings with different thickness and imide content, based on relative intensities of imide/styrene and imide/cellulose bands. The inhomogeneities were related to the formation of surface patterns for coatings with high viscosity and presence of non-imidized residues. From detailed surface maps (1 × 1 mm2), sensitive Raman bands were selected to describe variations in imide and styrene concentrations, conformations and interactions with fillers and cellulose. Based on data from Raman analysis, interactions between nanoparticles and cellulose possibly happened through hydrogen bonding.