Entropy of cellulose dissolution in water and in the ionic liquid 1-butyl-3-methylimidazolim chloride

Abstract

The entropic driving forces of cellulose dissolution in water and in the ionic liquid 1-butyl-3-methylimidazolium chloride (BmimCl) are investigated via molecular dynamics simulations and the two-phase thermodynamic model. An atomistic model of cellulose was simulated at a dissociated state and a microfibril state to represent dissolution. The calculated values of entropy and internal energy changes between the two states inform the interplay of energetic and entropic driving forces in cellulose dissolution. In both water and BmimCl, we found that the entropy associated with the solvent degrees of freedom (DOF) decreases upon cellulose dissolution. However, solvent entropy reduction in BmimCl is much smaller than that in water and counteracts the entropy gain from the solute DOF to a much lesser extent. Solvent entropy reduction in water also plays a major role in making the free energy change of cellulose dissolution unfavorable at room temperature. In BmimCl, the interaction energies between solvent molecules and glucan chains and the total entropy change both contribute favorably to the dissolution free energy of cellulose. Calculations at different temperatures in the two solvents indicate that changes in total internal energy are a good indicator of the sign of the free energy change of cellulose dissolution.

Dissolving process of a cellulose bunch in ionic liquids: a molecular dynamics study

“…All the simulation indicated that anions form strong H-bonds with hydroxyl groups in cellulose while imidazolium rings have close contact with the polysaccharide. [48][49][50][51] Jarin et al 48 used a PTMetaD-WTE approach to study the equilibrium glucose ring structure in BmimCl and BmimBF 4 , providing new insights into the potential energy surface towards the dissolution mechanism. [45][46][47] Zhao et al 45 explained why a certain amount of aprotic solvents can improve the solubility of cellulose.…”

“…Other research paid attention to the effect of additive solvents. Gross et al 49,50 studied two extreme states of cellulose in both BmimCl and water. Huo et al 46 proposed an indicator named ''Pair Energy Distribution'' to determine which kind of solvent could dissolve cellulose better.…”

Using Molecular Simulation to Study Biocatalysis in Ionic Liquids

“…Similar to the analysis methods for studying enzymes in ILs, many studies of substrates in ILs have focused on determining the solvent's structural and spatial distribution around the substrate to, for example, glean mechanistic aspects of cellulose solvation and dissolution in ILs (Cho, Gross, & Chu, 2011;Gross, Bell, & Chu, 2011;Gupta, Hu, & Jiang, 2011;Mostofian, Smith, & Cheng, 2011;Youngs, Hardacre, & Holbrey, 2007;Youngs et al, 2011). Thermodynamic analysis of the cellulose solvation process in ILs has revealed an entropic and energetic driving force for cellulose dissolution in ILs Gross, Bell, & Chu, 2012), and more recently published papers have identified key structural and thermodynamic differences of bundles of cellulose vs individual chains in ILs (Li et al, 2015;Rabideau, Agarwal, & Ismail, 2013;Rabideau & Ismail, 2015;Zhao, Liu, Wang, & Zhang, 2013). New and interesting methods of analysis include analyzing the induced changes in the conformational free energy landscapes of sugar rings by ILs (Jarin & Pfaendtner, 2014), and performing dynamical calculations of mean lifetimes of different binding states of IL anions with hydroxyl groups on cellulose (Rabideau & Ismail, 2015).…”

Cellulose dissolution: insights on the contributions of solvent-induced decrystallization and chain disentanglement

“…However, molecular dynamics simulations can predict the entropy change of cellulose dissolution in [bmim]Cl, i.e., the difference between the entropy in the microfibril state and the entropy when the chains are totally dissociated, which is around 8.37 J/K/molglucan and is not sensitive to temperature (cellulose was considered as a microfibril with 36 glucan chains and degree of polymerization 16) (Gross et al 2012). In our study the entropy change of decrystallization, i.e., the difference between the entropies of crystalline and amorphous state in which the chains are still entangled, is 2.47 J/K/mol-glucan.…”