Viscous flow properties and hydrodynamic diameter of phenothiazine-based redox-active molecules in different supporting salt environments
| Autor: | Lei Cheng, N. Harsha Attanayake, Aman Preet Kaur, Zhou Yu, Thilini M. Suduwella, Susan A. Odom, Randy H. Ewoldt, Yilin Wang |
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| Jazyk: | angličtina |
| Rok vydání: | 2020 |
| Předmět: |
Fluid Flow and Transfer Processes
Physics Mechanical Engineering Intrinsic viscosity Diffusion Computational Mechanics FOS: Physical sciences Viscometer Thermodynamics Condensed Matter - Soft Condensed Matter Condensed Matter Physics 01 natural sciences 010305 fluids & plasmas Shear rate Solvent Viscosity chemistry.chemical_compound chemistry Mechanics of Materials 0103 physical sciences Soft Condensed Matter (cond-mat.soft) Density functional theory 010306 general physics Acetonitrile |
| Popis: | We report viscous flow properties of a redox-active organic molecule, N-(2-(2-methoxyethoxy)ethyl)phenothiazine (MEEPT), a candidate for non-aqueous redox flow batteries, and two of its radical cation salts. A microfluidic viscometer enabled the use of small sample volumes in determining viscosity as a function of shear rate and concentration in the non-aqueous solvent, acetonitrile, both with and without supporting salts. All solutions tested show Newtonian behavior over shear rates of up to 30,000 1/s, which is rationalized by scaling arguments for the diffusion-based relaxation time of a single MEEPT molecule without aggregation. Neat MEEPT is flowable but with a large viscosity (412 mPa s) at room temperature), which is approximately 1,000 times larger than acetonitrile. When dissolved in acetonitrile, MEEPT solutions have low viscosities; at concentrations up to 0.5 M, the viscosity increases by less than a factor of two. From concentration-dependent viscosity measurements, molecular information is inferred from intrinsic viscosity (hydrodynamic diameter) and the Huggins coefficient (interactions). Model fit credibility is assessed using the Bayesian Information Criterion (BIC). It is found that the MEEPT and its charged cation are "flowable" and do not flocculate at concentrations up to 0.5 M. MEEPT has a hydrodynamic diameter of around 0.85 nm, which is largely insensitive to supporting salt and state of charge. This size is comparable to molecular dimensions of single molecules obtained from optimized structures using density function theory calculations. The results suggest that MEEPT is a promising candidate for redox flow batteries in terms of its viscous flow properties. 22 pages, 11 figures in manuscript; 8 pages, 5 figures in supporting information |
| Databáze: | OpenAIRE |
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