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This review covers the recently discovered methylcellulose (MC) fibrils and their impact on MC thermogelation and overall gel strength. The thermogelation of MC aqueous solutions has been studied for nearly 100 years, but it has only recently been attributed to fibril formation at elevated temperatures. The assembly of a fibrillar network explains the general features of MC gels: the unusually high modulus, the turbidity, and the nonlinear rheological behavior at high strains. Recent scattering, atomic force microscopy (AFM) and cryogenic transmission electron microscopy (cryo-TEM) experimental efforts have led to critical discoveries about the fibril structure. MC fibrils are 60% water by volume when in solution. The length of the fibrils, especially for shorter chains, is closely correlated with the MC chain contour length. On the other hand, the fibril radius does not depend on the temperature, molecular weight or concentration of MC chains but does seem to be correlated with chain stiffness. The discovery of MC fibrils represents a significant departure from the entanglement of polymer chains and localized phase separation based physical model of MC gelation, opens new questions about the mechanism of fibril formation and presents new pathways for stimulus responsive material design.
Bibliographical noteFunding Information:
A portion of this work has been supported by the National Science Foundation through the University of Minnesota MRSEC under Award Number DMR‐1420013. We thank the 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 the Dow Chemical Company. This research used resources of the Advanced Photon Source, a US 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 SANS experiments were conducted at Oak Ridge National Laboratory and NIST (Gaithersburg, MD, USA). The research conducted at ORNL's High Flux Isotope Reactor was sponsored in part by the Scientific User Facilities Division, Office of Basic Energy Sciences, US Department of Energy. I would like to acknowledge Dr Timothy P. Lodge, Dr Peter W. Schmidt, McKenzie L. Coughlin, Dr S. Piril Ertem and Dr Frank S. Bates for their discussions. Without them this research would not be possible.
© 2019 Society of Chemical Industry
- fibril assembly
- thermoreversible gelation
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