Browsing by Author "Roksana Markiewicz"

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Cation-Cation, Cation-Anion, and Anion-Anion Translation Diffusion in Ionic Liquids─Insight from NMR Relaxometry
(American Chemical Society, 2025) Elzbieta Masiewicz; Roksana Markiewicz; Rajendra K. Singh; Sujeet Kumar Chaurasia; Danuta Kruk
1H and 19F spin-lattice relaxation experiments have been performed for a series of ionic liquids: [HMIM][TFSI], [OMIM][TFSI], and [DMIM][TFSI] including the same anion and cations with progressively longer alkyl chains. The experiments were performed in a wide frequency range from 10 kHz to 10 MHz (referring to the 1H resonance frequency) versus temperature. This extensive data set has been analyzed in terms of a theoretical model including all relevant homonuclear (1H-1H and 19F-19F) and heteronuclear (1H-19F) relaxation pathways and linking the relaxation features to the relative translational diffusion between the ion pairs (cation-cation, cation-anion, and anion-anion). In addition to the comprehensive theoretical approach, closed-form expressions have been provided and applied to determine the diffusion coefficients from the slopes of the linear dependences of the relaxation rates on the square root of the resonance frequency. The combined experimental and theoretical studies have led to the determination of the complete set of diffusion coefficients, forming a consistent picture of the dynamical scenario. In addition to revealing the dynamical properties of the liquids and the influence of the subtle changes in the cation structure on the movement of both cations and anions, the theoretical means for exploiting Nuclear Magnetic Resonance relaxometry for ionic liquids have been provided. © 2024 American Chemical Society.
Dynamics of ionic liquids by means of nuclear magnetic resonance relaxation - overview of theoretical approaches
(Royal Society of Chemistry, 2024) Danuta Kruk; Elzbieta Masiewicz; Roksana Markiewicz; Rajendra Kumar Singh
This paper presents a comprehensive overview of the spin relaxation theory needed for exploring nuclear magnetic resonance (NMR) relaxometry to study the dynamical properties of ionic liquids. The term NMR relaxometry refers to relaxation experiments performed over a wide range of magnetic fields (resonance frequencies). In this way, dynamical processes occurring on timescales from milliseconds to nanoseconds can be studied, including translational and rotational dynamics of both types of ions (cations and anions). In order to take advantage of the remarkable experimental possibilities, appropriate theoretical models linking relaxation properties with ionic motion are needed. With the aim of providing such theoretical tools, 1H and 19F relaxation models for ionic liquids have been reviewed and their applications have been illustrated by several examples. The presented models are valid for an arbitrary magnetic field, include all relevant relaxation pathways and allow to extract detailed information about the translational and rotational dynamics of the ions. On the basis of the theoretical models, formulas allowing a straightforward determination of the translational diffusion coefficients of cations and anions from combined 1H and 19F relaxation studies have been derived and discussed in detail. © 2024 The Royal Society of Chemistry.