An insight into the dissolution of cellulose in 1-butyl-3-methylimidazolium chloride-DMSO binary Mixture: Exploring the dynamics of rhodamine 6G and fluorescein

The change in the interaction of solute and the ionic liquid-DMSO mixture with the extent of dissolution of cellulose is investigated through fluorescence spectroscopic studies. This study aims to provide an insight into the dissolution of cellulose in ionic liquid-DMSO mixtures in terms of photophysical aspects. Although the rheology and viscoelastic properties of ionic liquid-DMSO-cellulose mixtures are well studied in the early literature, there is a lack of photophysical investigation. For this reason, we have taken two oppositely charged but structurally similar solutes, fluorescein sodium salt (Fl-Na) and rhodamine 6G (R6G), to investigate their rotational and translational dynamics in the mixture. Analysis of the time-resolved fluorescence anisotropy data using the Stokes-Einstein-Debye (SED) theory suggests that the rotational relaxation times of the solutes follow near stick hydrodynamics in absence of cellulose. The solutes experienced a strong interaction in pure DMSO and with the increasing concentration of BmimCl, the specific interaction between the solvent and the solute decreases as indicated in decreasing Cobs values. While in presence of cellulose, the solutes follow near slip hydrodynamics in low BmimCl concentration but at higher concentration, the specific interaction increases. From the temperaturedependent anisotropy, we have observed that both R6G and Fl-Na follows the super-stick trend, and with increasing temperature specific interaction between the solute and solvent increases. On the other hand, in presence of cellulose, their rotational reorientation times appear close to the slip boundary condition at low temperature, and with increasing temperature, it approaches close to the stick boundary. Fluorescence Correlation Spectroscopy (FCS) indicates the presence of structural heterogeneity in the BmimCl-DMSO mixture formed due to the segregation of the hydrophobic chain of the ionic liquid. Therefore, the experimental results of this work suggest that the dissolution of cellulose modulates the dynamics of the solutes in ionic liquid-DMSO mixtures. (C) 2021 Elsevier B.V. All rights reserved.

Automated summary

This study investigates the interaction between solutes and an ionic liquid-DMSO mixture with varying levels of cellulose dissolution through fluorescence spectroscopic studies. The results indicate that the presence of cellulose modulates the dynamics of solutes in the mixture, leading to specific interaction patterns and temperature-dependent changes in rotational reorientation times. Overall, this work highlights the importance of understanding the photophysical aspects of cellulose dissolution in ionic liquid-DMSO mixtures.