Paper Number
VP28 

Session
Pre-recorded Flash Presentations (virtual)

Title
Charge screening effects on the rheology of polymerized ionic liquid solutions in the semidilute unentangled regime

Presentation Date and Time
All Week (Asynchronous) Any Time

Track / Room
Pre-recorded Presentation / Virtual

Authors (Click on name to view author profile)

1. Matsumoto, Atsushi (University of Fukui, Applied Chemistry and Biotechnology)
2. Yoshizawa, Ryota (Osaka University, Macromolecular Science)
3. Urakawa, Osamu (Osaka University, Macromolecular Science)
4. Inoue, Tadashi (Osaka University, Macromolecular Science)
5. Shen, Amy Q. (Okinawa Institute of Science and Technology, MicroBioNanofluidics Unit)

Author and Affiliation Lines (in printed abstract book)
Atsushi Matsumoto¹, Ryota Yoshizawa², Osamu Urakawa², Tadashi Inoue² and Amy Q. Shen^3
1Applied Chemistry and Biotechnology, University of Fukui, Fukui-shi, Fukui 9108507, Japan; ²Macromolecular Science, Osaka University, Toyonaka-shi, Osaka 5600043, Japan; ³MicroBioNanofluidics Unit, Okinawa Institute of Science and Technology, Onna-son, Okinawa 9040495, Japan

Speaker / Presenter 
Matsumoto, Atsushi

Keywords
polymer solutions

Text of Abstract
Polymerized ionic liquids (PILs) are a new class of polyelectrolytes with ionic liquid (IL) structures on their repeating units. The viscoelastic properties of PILs in IL solutions can be affected by the charge screening of PIL chains by IL ions. However, the effect of IL charge screening on the viscoelasticity of PIL solutions has not been well understood yet, especially at high IL concentrations where the classical Debye-Hückel (DH) theory becomes inapplicable. In this work, we aim to understand the effect of the ionic correlation on the rheology of PIL in IL solutions in the semidilute unentangled (SU) polymer regime. We conduct detailed rheological characterization of an imidazolium-based PIL (PC4-TFSI) in a mixture of salt-free solvent (DMF) and an IL (Bmim-TFSI) possessing a similar ionic structure to that of the PIL repeating unit. The specific viscosity (η_sp) of PC4–TFSI solutions is measured at varying IL concentrations (c_IL) while keeping the polymer concentration fixed. We find that: i) η_sp remains as a constant at low c_IL; (ii) η_sp decreases with increasing c_IL at an intermediate c_IL, in good agreement with the behavior of ordinary polyelectrolytes attributed to the DH screening at low salt concentrations; (iii) η_sp increases at c_IL>1 M. We have captured the observed trend of η_sp versus c_IL by proposing and validating a new charge screening model which accounts for the modified screening length and complete charge screening at high IL concentrations. Our model suggests that extended PIL chains initially shrink due to the conventional charge screening effect at low IL concentrations, but revert to expanded configuration at higher IL concentrations due to strong ionic correlations.