Abstract text (incl. figure legends and references)

The aim of the project was to perform a 3-dimensional reconstruction of isotropic and anisotropic polymer particles embedded in polymer films using volume SEM (Serial Blockface Imaging, SBFI). For this purpose, isotropic polystyrene (PS) particles with diameter of 1.4 µm were incorporated in PVA films from aqueous solution. To gain anisotropic ellipsoidal particles, the films were stretched unidirectional at different strain ratios above the glass transition point of PS. [1, 2]. Optimization of the sample preparation method for SBFI SEM included contrasting the PVA films with cesium chloride, and addition of 344 nm silica particles during film production as alignment support for the reconstruction. The particle-film samples were embedded in conductive silver epoxy resin, trimmed and cut using SBFI-SEM (Apreo VS, ThermoScientific/FEI) at 40 nm Z-axis and a total volume thickness of at least 12 µm (min. 300 slices) in low-vac mode to reduce charging artifacts. Image stacks were reconstructed using AMIRA software, utilizing the fiducial silica particles for optimized alignment of the images. Morphometric analysis of the PS particles took place after segmentation, following an optimized image data processing routine. Shrinking of the PVA films due to evaporation of residual water content despite equilibration in low vacuum led to deformation artifacts of the reconstructed PS particles. These could be corrected with an approach based on the geometric data of the silica fiducials. The morphological parameters of thus corrected 3D reconstructed PS particles of all stretching conditions correlated well with measurements of the particles isolated from the films in standard SEM. In summary, we could establish a sufficiently accurate 3D reconstruction and analysis of polymer particle/polymer film-systems using SBFI-REM.

References:

Ho C. C., K. A., Odell J. A., Ottewill R. H., Preparation of monodisperse ellipsoidal polystyrene particle. Colloid and Polymer Science 1993, 271, 469-479. Champion, J. A.; Katare, Y. K.; Mitragotri, S., Making polymeric micro- and nanoparticles of complex shapes. Proc Natl Acad Sci U S A 2007, 104 (29), 11901-11904.