Abstract
As a water-soluble cellulose ether, methylcellulose (MC) is used in a variety of applications that take advantage of its thermoreversible gelation. Recent work has shown that MC gelation is due to the formation of nanofibrils with a relatively uniform diameter (ca. 15 nm) and that gelation and fibril formation can be suppressed through the addition of low-molecular-weight poly(ethylene glycol) as grafts along the backbone. In this work, we modify MC similarly with thiol-terminated poly(N-isopropylacrylamide) (PNIPAm, Mw ≈ 3 kg/mol) using thiol-ene click chemistry and investigate the resulting influence on aqueous MC solution properties. From static and dynamic light scattering, it is apparent that the coil dimensions increase with grafting density (up to 0.11 grafts/anhydroglucose repeat unit), which leads to an increase in the persistence length inferred from the Kratky-Porod wormlike chain model. The data are consistent with a model based on the incorporation of graft-graft and graft-backbone excluded volume interactions. Interestingly, grafting PNIPAm leads to an increase in the theta temperature, even though PNIPAm typically has a lower critical solution temperature (LCST) that is lower than bare MC. Small-angle X-ray scattering and cryogenic transmission electron microscopy reveal that fibril formation still occurs at high temperature for the grafted chains.
| Original language | English (US) |
|---|---|
| Pages (from-to) | 550-558 |
| Number of pages | 9 |
| Journal | Macromolecules |
| Volume | 55 |
| Issue number | 2 |
| DOIs | |
| State | Published - Jan 25 2022 |
| Externally published | Yes |
Bibliographical note
Funding Information:This work was supported by the National Science Foundation through the University of Minnesota MRSEC under Award Numbers DMR-1420013 and DMR-02011401, as well as by the National Science Foundation Graduate Research Fellowship Program (M.L.C.) under Grant Numbers 00039202 and 00074041. The authors 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 was 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 No. DE-AC02-06CH11357. Data were collected using an instrument funded by the National Science Foundation under Award Number 0960140. The cryo-TEM images were collected at the Characterization Facility, University of Minnesota, which receives partial support from NSF through the MRSEC program. The authors thank Dr. Svetlana Morozova and Dr. S. Piril Ertem for helpful discussions regarding synthesis and light scattering experiments, as well as Dr. Peter W. Schmidt for insightful discussions regarding X-ray characterization and cryo-TEM experiments.
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