Heterogeneity in Ionic Liquids and Deep Eutectic Solvents: A Molecular Dynamics Simulation Approach

Banerjee, Swarup (2022) Heterogeneity in Ionic Liquids and Deep Eutectic Solvents: A Molecular Dynamics Simulation Approach. PhD thesis, Indian Institute of Science Education and Research Kolkata.

Text (PhD thesis of Swarup Banerjee (14IP012)) 14IP012.pdf - Submitted Version Restricted to Repository staff only Download (13MB)

Abstract

The presence of long-range interactions in a given reaction medium often predicts the consequence of a chemical reaction, as such interactions can introduce heterogeneities, which incorporate various spatial and dynamical features in the medium. Ionic liquids (ILs) and Deep eutectic solvents (DESs), which resemble each other via ion-ion, ion-dipole, and dipole-dipole interactions, have tremendous application potential in technologies and industries as a reaction media owing to their minimal hazardous nature. They also offer an excellent avenue to explore some of the critical heterogeneity features at or around room temperature, even though their glass transition temperature is much lower than the room temperature. DESs (can be both ionic and non-ionic) are multicomponent mixtures that can attain a liquid state near room temperature on mixing at a particular mole fraction, although individual melting temperatures of the constituents have a much higher value than the room temperature. The charge delocalization through the extensive interspecies hydrogen bonding and the entropic gain in the liquid state induces a deep depression of the freezing point, attributing to the lower melting point of the mixture. In contrast, ILs consist exclusively of ions, and most of the ILs remain in a liquid state below 373 K. ILs are also termed "designer solvents" because the constituents (cations and anions) of the mixtures are extensively available, and each has its specific application. The high viscosity of neat ILs is detrimental to their use as solvents in many industrial purposes. However, the presence of polar solvents such as water and alcohols can dramatically alter their physicochemical properties, such as viscosity, surface tension, polarity, etc. Nonetheless, more competent and practical applications of these intriguing solvents demand a thorough investigation of structure and dynamics as a profound knowledge of medium heterogeneity is a prerequisite to liquid solvent engineering for tailoring a reaction. This thesis primarily focuses on studying the impact of heterogeneity on the essential molecular level interaction and dynamics of ILs and DESs. We have performed all-atom and united-atom molecular dynamic (MD) simulations to explore the structure and dynamics, emphasizing the signatures of pronounced spatial and temporal heterogeneities in these systems.

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