Molecular Weight Dependence of Methylcellulose Fibrillar Networks

Peter W. Schmidt, Svetlana Morozova, Paige M. Owens, Roland Adden, Yongfu Li, Frank S. Bates, Timothy P Lodge

Research output: Contribution to journalArticlepeer-review

16 Scopus citations

Abstract

Gelation of aqueous methylcellulose (MC) solutions upon heating has been shown to result from the formation of a network of semiflexible fibrils, with diameters of 15 ± 2 nm. Here, we investigate the impact of MC molecular weight on the elasticity and structure of aqueous gels at concentrations between 0.1 and 3 wt %. Small-amplitude oscillatory shear measurements conducted at a fixed concentration reveal that the gel modulus increases monotonically by a factor of 5 for weight-average molecular weights (Mw) between 22 and 550 kg/mol. Small-angle X-ray scattering data, fit to a semiflexible cylinder model, demonstrate that the fibril radius, Kuhn length, and volume fraction are approximately constant throughout this molecular weight range. Small-angle light scattering shows that the fibrillar-rich and fibrillar-depleted domains within the gel are associated with an essentially invariant heterogeneity correlation length. Direct visualization by cryo-TEM reveals that lower molecular weight MC forms fibrils of lower average length. The distribution of fibril lengths measured by cryo-TEM and the distribution of the polymer chain contour lengths are similar, especially for shorter chains, and these features are correlated to network connectivity. We propose that the underlying fibril structure consists of bundles of polymer chains with a preferred orientation coincident with the fibril axis, while the fibril diameter is controlled by a circumferential helical pitch associated with the single chain Kuhn length and interactions between chains.

Original languageEnglish (US)
Pages (from-to)7767-7775
Number of pages9
JournalMacromolecules
Volume51
Issue number19
DOIs
StatePublished - Oct 9 2018

Bibliographical note

Funding Information:
This work was supported primarily by the National Science Foundation through the University of Minnesota MRSEC under Award DMR-1420013. 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 The 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 DE-AC02 06CH11357.

Funding Information:
This work was supported primarily by the National Science Foundation through the University of Minnesota MRSEC under Award DMR-1420013. 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 The 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 DE-AC02-06CH11357. The SAXS fitting in this work benefited from the use of the SasView application, originally developed under NSF Award DMR-0520547. SasView contains code developed with funding from the European Union’s Horizon 2020 research and innovation programme under the SINE2020 project, Grant Agreement No. 654000. The cryo-TEM images were collected at the Characterization Facility, University of Minnesota, which receives partial support from NSF through the MRSEC program.

Publisher Copyright:
© 2018 American Chemical Society.

How much support was provided by MRSEC?

  • Primary

Reporting period for MRSEC

  • Period 5

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