Projects per year
Abstract
The weight-average molecular weight Mw, z-average radius of gyration Rg, and second virial coefficient A2 have been determined between 15 and 52°C for dilute aqueous solutions of methylcellulose (MC) with three different molecular weights and constant degree of substitution (DS) of 1.8 using static light scattering. These measurements, conducted within 1 h of heating the homogeneous solutions from 5°C, reveal that the theta temperature for MC in water is Tθ = 48 ± 2°C, with A2 < 0 for T > Tθ, indicative of lower critical solution temperature (LCST) behavior. However, after annealing a solution for 2 days at 40°C evidence of high molecular weight aggregates appears through massive increases in the apparent Mw and Rg, a process that continues to evolve for at least 12 days. Cryogenic transmission electron microscopy images obtained from a solution aged for 3 weeks at 40°C reveal the presence of micron size fibrils with a diameter of 16 ± 4 nm, structurally analogous to the fibrils that form upon gelation of aqueous MC solutions at higher concentrations and elevated temperatures. Growth of fibrils from a solution characterized by a positive A2 indicates that semiflexible MC dissolved in water is metastable at T < Tθ, even though the solvent quality is apparently good. The minimum temperature required for MC solutions to aggregate is estimated to be 30°C, based on the rate-independent gel-to-solution transition determined by small-amplitude oscillatory shear measurements conducted while cooling 0.5 and 5.0 wt % solutions. These results cannot be explained based solely on separation into two isotropic phases upon heating using classical Flory-Huggins solution theory. We speculate that the underlying equilibrium phase behavior of aqueous MC solutions involves a nematic order parameter.
Original language | English (US) |
---|---|
Pages (from-to) | 7205-7215 |
Number of pages | 11 |
Journal | Macromolecules |
Volume | 48 |
Issue number | 19 |
DOIs | |
State | Published - Sep 24 2015 |
Bibliographical note
Publisher Copyright:© 2015 American Chemical Society.
How much support was provided by MRSEC?
- Partial
Reporting period for MRSEC
- Period 2
Fingerprint
Dive into the research topics of 'Thermodynamics of Aqueous Methylcellulose Solutions'. Together they form a unique fingerprint.-
MRSEC IRG-3: Hierarchical Multifunctional Macromolecular Materials
Reineke, T. M., Bates, F. S., Dorfman, K., Dutcher, C. S., Hillmyer, M. A., Lodge, T., Morse, D. C., Siepmann, I., Barreda, L. & Ganewatta, M. S.
1/1/98 → …
Project: Research project
-