Structure-property relationships in Polyethylene (PE) films require correlations between multiple characterization techniques. In order to compare AFM images to SAXS images of multiple PE films, improved AFM imaging and image analysis is necessary. In bimodal AFM, the cantilever is simultaneously excited at two eigenmodes which results in enhanced sensitivity and spatial resolution as a result of cantilever vibrational mode coupling. This allows bimodal AFM to directly image crystalline and amorphous regions in a blown PE film without the need for selective etching. The spatial resolution and contrast of the PE film morphology can be further improved by utilizing super sharp diamond cantilevers which have a 2 nm radius. PE blown films from linear low density PE (LLDPE) were examined for their surface and bulk morphologies. Differences in lamellar spacing, orientation and size were observed at high magnification and high resolution in the microtomed bulk of these films, including clear orientation and stacked lamellar crystals along the machine and transverse direction. Poorly assembled spherulites can be observed at the film surface which may have resulted from two-dimensional surface crystallization and can be correlated with film haze. With a strong phase contrast between crystalline and amorphous regions in these PE blown films, a Fast Fourier Transform (FFT) was applied to transform phase images in the bulk from real space into reciprocal space, revealing the spacing of lamellae and their orientation. Microbeam Small Angle X-ray Scattering (SAXS) images were collected edge-on in the same orientation as the AFM images and show clear lamellar orientation similar to the AFM FFT images. Combined AFM phase and FFT images with SAXS images allows for a direct comparison between real and reciprocal space for better morphological characterization of PE films which are then linked to film properties.

Lamellae morphology of polyethylene blown films by bimodal AFM

256th National Meeting (2018)

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