Jennifer Donohue1,Steven Zeltmann1,Karen Bustillo2,Benjamin Savitzky2,Mary Ann Jones3,Gregory Meyers3,Colin Ophus2,Andrew Minor1
University of California, Berkeley1,Lawrence Berkeley National Laboratory2,Dow3
Jennifer Donohue1,Steven Zeltmann1,Karen Bustillo2,Benjamin Savitzky2,Mary Ann Jones3,Gregory Meyers3,Colin Ophus2,Andrew Minor1
University of California, Berkeley1,Lawrence Berkeley National Laboratory2,Dow3
Understanding the local nanoscale structure in heterogenous polymer nanocomposites and blends, particularly at and near interfaces, is critical in understanding the resulting bulk properties and completing the feedback loop for improved materials design. However, observing these structures has been a challenge as there are few to no techniques which can achieve nanoscale resolution, and provide information about the local atomic ordering, crystalline and amorphous, in polymeric materials which express heterogeneous structure on the nanoscale.<br/>Four-dimensional scanning transmission electron microscopy(4D-STEM) a recently popularized nanobeam diffraction technique promises the needed resolution and structural information<sup>[1]</sup>. However, beam damage and low scattering contrast from low Z elements has severely limited its application into the study of polymeric materials<sup>[2]</sup>. Now, with the recent advances in high-speed direct electron detectors, and electron counting algorithms, coupled with energy filtration and cryogenic holders, which provide vast improvements in electron dose control and signal-to-noise ratio, there is potential for expanding this technique to characterize local structure in beam-sensitive polymer composites<sup>[2]</sup>. In addition to experimental considerations, 4D-STEM produces large amounts of complex high-dimensional data requiring a processing algorithm to extract meaningful structural information<sup>[1]</sup>.<br/>In this presentation we demonstrate a low-dose 4D-STEM technique and an accompanying processing routine for visualizing nanostructure in beam sensitive semicrystalline isotactic polypropylene and ethylene-octene copolymer (iPP/EOC) films with 5nm resolution. We use a two-step routine to map the amorphous phase distribution, and the crystalline structure. Our method is able to overcome the beam sensitivity, chemical and structural similarity, and low diffraction contrast limitations to image this multiphase polymer sample. This technique opens the door to direct observation of nanostructure in polymer blends and nanocomposites without heavy metal staining.<br/>References:<br/>[1] C. Ophus, Microsc. Microanal., <b>25</b>(3), 563-582 (2019).<br/>[2] K.C. Bustillo <i>et al</i>, Acc. Chem. Res. <b>54</b>, 2543–2551 (2021).<br/>[3]S.A. Rabiej, Eur. Polym. J. <b>27</b>, 947–954 (1991).<br/>[4] F.P.T.J. Van der Burgt <i>et al</i>, J. Macromol. Sci. - Phys<i>.</i> <b>41 B</b>, 1091–1104 (2002).<br/>[5] L. Godail and D.E. Packham, J. Adhes. Sci. Technol<i>.</i> <b>15</b>, 1285–1304 (2001).