Holger Schmalz: Raman imaging as versatile tool for the characterization of multicomponent polymer particles/fibers and mesostructured stystems

Raman imaging is an excellent tool for the characterization of multicomponent polymer fibers and microparticles, as well as complex mesostructured materials. The inherent lack of a sufficient electron density contrast between different polymers limits the use of scanning (SEM) and transmission (TEM) electron microscopy for the characterization of multicomponent polymer structures in the μm-range, as usually a selective staining of one of the polymer phases with heavy elements is necessary. However, selective staining methods are only available for specific polymer combinations and a time-consuming sample preparation, like the preparation of ultra-thin sections for TEM, is often required. Here, confocal Raman imaging with a lateral resolution of about 300 nm allows to directly determine the spatial distribution of the polymeric components without the need of a preceding sample preparation, as the chemically different polymers can be easily identified via specific Raman bands.

As an example, Fig. 1A, B depicts the morphology of bicomponent fibers produced by side-by-side electrospinning (the two different polymers are colored in red and blue).[1] Depending on the employed solvent a Janus-type (Fig. 1A) or bead-like (Fig. 1B) structure, where the beads exhibit a core-shell morphology, is formed. Fig. 1C shows the successful encapsulation of bacteria (colored in red) within a poly(vinyl alcohol) microparticle (colored in blue), produced by a facile emulsion process. These biohybrid microparticles can be incorporated into a pH-responsive fiber mat, which was utilized for phenol degradation under acidic conditions, where neat bacteria will not survive.[2]