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Methylcellulose (MC) is a water-soluble cellulose derivative with a wide range of commercial applications. Upon heating, MC solutions reversibly form â15-20 nm diameter fibrils, which percolate into a fibrillar network, resulting in macroscopic gelation. Using mid-angle X-ray scattering (MAXS) and wide-angle X-ray scattering (WAXS), we have analyzed MC chain organization within fibrils aligned in dried films that have been stretched by over 300%. MAXS and WAXS show distinct anisotropic scattering features, which we interpret as reflecting crystalline domains within the fibrils. The scattering peaks are consistent with a body-centered monoclinic unit cell, with similar dimensions as other cellulosic crystals, a = 11.4 Å, b = 8.9 Å, and c = 10.2 Å, and γin the range of 90-100°, with MC chains oriented along the long axis of the fibril. Phase-plate cryogenic transmission electron microscopy images of MC fibrils contribute to a more comprehensive picture. Along the long axis of MC fibrils, there is evidence of dense twisted domains, which are interpreted as regions containing semicrystalline MC, interspersed with looser, less organized amorphous domains. Together, these two techniques provide the most complete interpretation of MC subfibril structure currently available.
Bibliographical noteFunding Information:
This work was supported primarily by the National Science Foundation through the University of Minnesota MRSEC under award number DMR-1420013. The authors thank Dow Chemical Company for generously providing the MC samples. The SAXS measurements were taken at the DuPont-Northwestern-Dow Collaborative Access Team (DND-CAT) located at Sector 5 of the Advanced Photon Source (APS). DND-CAT is supported by Northwestern University, E.I. DuPont de Nemours & Co., and Dow Chemical Company. This research used resources of the Advanced Photon Source, a U.S. Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under contract no. DE-AC02-06CH11357. The phase-plate cryo-TEM work was performed at the Technion Center for Electron Microscopy of Soft Matter, supported by the Technion Russell Berrie nanotechnology Institute (RBNI). The cryo-TEM images were collected at the Characterization Facility, University of Minnesota, which receives partial support from NSF through the MRSEC program.
Copyright © 2020 American Chemical Society.
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