Gelation, Phase Separation, and Fibril Formation in Aqueous Hydroxypropylmethylcellulose Solutions
| Autor: | Robert L. Sammler, Svetlana Morozova, Frank S. Bates, John W. McAllister, Peter W. Schmidt, Timothy P. Lodge, Joseph Lott, Yongfu Li, Amanda Maxwell |
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| Rok vydání: | 2018 |
| Předmět: |
Materials science
Polymers and Plastics Nanofibers Bioengineering 02 engineering and technology Methylcellulose Neutron scattering 010402 general chemistry 01 natural sciences Light scattering Biomaterials X-Ray Diffraction Rheology Materials Chemistry Aqueous solution Small-angle X-ray scattering Scattering Drop (liquid) Cryoelectron Microscopy 021001 nanoscience & nanotechnology 0104 chemical sciences Condensed Matter::Soft Condensed Matter Neutron Diffraction Chemical engineering Turbidimetry 0210 nano-technology |
| Zdroj: | Biomacromolecules. 19:816-824 |
| ISSN: | 1526-4602 1525-7797 |
| DOI: | 10.1021/acs.biomac.7b01611 |
| Popis: | The thermoresponsive behavior of a hydroxypropylmethylcellulose (HPMC) sample in aqueous solutions has been studied by a powerful combination of characterization tools, including rheology, turbidimetry, cryogenic transmission electron microscopy (cryoTEM), light scattering, small-angle neutron scattering (SANS), and small-angle X-ray scattering (SAXS). Consistent with prior literature, solutions with concentrations ranging from 0.3 to 3 wt % exhibit a sharp drop in the dynamic viscoelastic moduli G' and G″ upon heating near 57 °C. The drop in moduli is accompanied by an abrupt increase in turbidity. All the evidence is consistent with this corresponding to liquid-liquid phase separation, leading to polymer-rich droplets in a polymer-depleted matrix. Upon further heating, the moduli increase, and G' exceeds G″, corresponding to gelation. CryoTEM in dilute solutions reveals that HPMC forms fibrils at the same temperature range where the moduli increase. SANS and SAXS confirm the appearance of fibrils over a range of concentration, and that their average diameter is ca. 18 nm; thus gelation is attributable to formation of a sample-spanning network of fibrils. These results are compared in detail with the closely related and well-studied methylcellulose (MC). The HPMC fibrils are generally shorter, more flexible, and contain more water than with MC, and the resulting gel at high temperatures has a much lower modulus. In addition to the differences in fibril structure, the key distinction between HPMC and MC is that the former undergoes liquid-liquid phase separation prior to forming fibrils and associated gelation, whereas the latter forms fibrils first. These results and their interpretation are compared with the prior literature, in light of the relatively recent discovery of the propensity of MC and HPMC to self-assemble into fibrils on heating. |
| Databáze: | OpenAIRE |
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