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Methylcellulose solutions are known to form microfibrils at elevated temperatures or in the presence of salt. The fibrils have a significant impact on the solution's rheological properties. Here, the shear and extensional properties of methylcellulose solutions with added salt are measured using hyperbolic microfluidic channels, allowing for new characterization at lower molecular weights and higher shear and strain rates that are difficult to access by macroscale rheology studies. 1 and 2 wt% methylcellulose solutions with molecular weight of 150 kg mol −1 with NaCl content between 0 to 5 wt% have been characterized. All solutions were found to be shear thinning, with power law thinning behavior at shear rates above 100 s −1 . The addition of NaCl up to 5 wt% had only small effects on shear viscosity at the shear rates probed (100 s −1 and 10 000 s −1 ). Extensional viscosities as low as 0.02 Pa s were also measured. Unlike the results for shear viscosity, the addition of 5 wt% NaCl caused significant changes in extensional viscosity, increasing by up to 10 times, depending on extension rate. Additionally, all solutions tested showed apparent extensional thinning in the high strain rate regime (>100 s −1 ), which has not been reported in other studies of methylcellulose solutions. These findings may provide insight for those using methylcellulose solutions in process designs involving extensional flows over a wide range of strain rates.
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Molecular dynamics simulations of the dielectric constants of salt-free and salt-doped polar solvents
We develop a Stockmayer fluid model that accounts for the dielectric responses of polar solvents (water, MeOH, EtOH, acetone, 1-propanol, DMSO, and DMF) and NaCl solutions. These solvent molecules are represented by Lennard-Jones (LJ) spheres with permanent dipole moments and the ions by charged LJ spheres. The simulated dielectric constants of these liquids are comparable to experimental values, including the substantial decrease in the dielectric constant of water upon the addition of NaCl. Moreover, the simulations predict an increase in the dielectric constant when considering the influence of ion translations in addition to the orientation of permanent dipoles.
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- Award ID(s):
- 1944211
- PAR ID:
- 10508057
- Publisher / Repository:
- AIP Publishing
- Date Published:
- Journal Name:
- The Journal of Chemical Physics
- Volume:
- 159
- Issue:
- 13
- ISSN:
- 0021-9606
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1063/5.0165481
