Modeling of Solid−Liquid Equilibria in Deep Eutectic Solvents: A Parameter Study

Deep eutectic solvents (DESs) are potential alternatives to many conventional solvents in process applications. Knowledge and understanding of solid–liquid equilibria (SLE) are essential to characterize, design, and select a DES for a specific application. The present study highlights the main aspects that should be taken into account to yield better modeling, prediction, and understanding of SLE in DESs. The work is a comprehensive study of the parameters required for thermodynamic modeling of SLE—i.e., the melting properties of pure DES constituents and their activity coefficients in the liquid phase. The study is carried out for a hypothetical binary mixture as well as for selected real DESs. It was found that the deepest eutectic temperature is possible for components with low melting enthalpies and strong negative deviations from ideality in the liquid phase. In fact, changing the melting enthalpy value of a component means a change in the difference between solid and liquid reference state chemical potentials which results in different values of activity coefficients, leading to different interpretations and even misinterpretations of interactions in the liquid phase. Therefore, along with reliable modeling of liquid phase non-ideality in DESs, accurate estimation of the melting properties of their pure constituents is of clear significance in understanding their SLE behavior and for designing new DES systems

Influence of the Molecular Structure of Constituents and Liquid Phase Non-Ideality on the Viscosity of Deep Eutectic Solvents

Hydrophobic deep eutectic solvents (DES) have recently been used as green alternatives to conventional solvents in several applications. In addition to their tunable melting temperature, the viscosity of DES can be optimized by selecting the constituents and molar ratio. This study examined the viscosity of 14 eutectic systems formed by natural substances over a wide range of temperatures and compositions. The eutectic systems in this study were classified as ideal or non-ideal based on their solid–liquid equilibria (SLE) data found in the literature. The eutectic systems containing constituents with cyclohexyl rings were considerably more viscous than those containing linear or phenyl constituents. Moreover, the viscosity of non-ideal eutectic systems was higher than that of ideal eutectic systems because of the strong intermolecular interactions in the liquid solution. At temperatures considerably lower than the melting temperature of the pure constituents, non-ideal and ideal eutectic systems with cyclohexyl constituents exhibited considerably high viscosity, justifying the kinetic limitations in crystallization observed in these systems. Overall, understanding the correlation between the molecular structure of constituents, SLE, and the viscosity of the eutectic systems will help in designing new, low-viscosity DES

Design of Deep Eutectic Systems: A Simple Approach for Preselecting Eutectic Mixture Constituents

Eutectic systems offer a wide range of new (green) designer solvents for diverse applications. However, due to the large pool of possible compounds, selecting compounds that form eutectic systems is not straightforward. In this study, a simple approach for preselecting possible candidates from a pool of substances sharing the same chemical functionality was presented. First, the melting entropy of single compounds was correlated with their molecular structure to calculate their melting enthalpy. Subsequently, the eutectic temperature of the screened binary systems was qualitatively predicted, and the systems were ordered according to the depth of the eutectic temperature. The approach was demonstrated for six hydrophobic eutectic systems composed of L-menthol and monocarboxylic acids with linear and cyclic structures. It was found that the melting entropy of compounds sharing the same functionality could be well correlated with their molecular structures. As a result, when the two acids had a similar melting temperature, the melting enthalpy of a rigid acid was found to be lower than that of a flexible acid. It was demonstrated that compounds with more rigid molecular structures could form deeper eutectics. The proposed approach could decrease the experimental efforts required to design deep eutectic solvents, particularly when the melting enthalpy of pure components is not available

Impact of the manufacturing technique on the dissolution-enhancement functionality of PEG4000 in Cilostazol tablets

Cilostazol was selected as poorly-soluble model drug to investigate the impact of the manufacturing method on the excipient functionality of PEG4000 at various levels. Powder blends were prepared by direct compression (DC), wet granulation (WG) and hot-melt extrusion (HME). Characteristics of these blends and their compressed tablets were investigated by standard techniques. Solid-state characterization was carried out using differential scanning calorimetry (DSC). While DC trials were found with no significant differences, WG and HME showed contrasting enhancement and retardation effects regarding the dissolution profile of Cilostazol tablets depending on the level of PEG4000 incorporated. The optimal enhancement of dissolution was obtained at 10% w/w PEG4000 for tablets prepared by HME. DSC analysis indicated that no solid solutions were formed at such low levels of PEG4000during processing by either manufacturing techniques. Consequently, the wetting functionality and dissolution enhancement of PEG4000 was revealed to be level- and manufacturing method dependent

Separation of Benzene and Cyclohexane Using Eutectic Solvents with Aromatic Structure

The separation of benzene and cyclohexane is a challenging process in the petrochemical industry, mainly because of their close boiling points. Extractive separation of the benzene-cyclohexane mixture has been shown to be feasible, but it is important to find solvents with good extractive performance. In this work, 23 eutectic solvents (ESs) containing aromatic components were screened using the predictive COSMO-RS and their respective performance was compared with other solvents. The screening results were validated with experimental work in which the liquid–liquid equilibria of the three preselected ESs were studied with benzene and cyclohexane at 298.5 K and 101.325 kPa, with benzene concentrations in the feed ranging from 10 to 60 wt%. The performance of the ESs studied was compared with organic solvents, ionic liquids, and other ESs reported in the literature. This work demonstrates the potential for improved extractive separation of the benzene-cyclohexane mixture by using ESs with aromatic moieties

Li(C2N3) as eutectic forming modifier in the melting process of the molecular perovskite [(C3H7)3N(C4H9)]Mn(C2N3)3±

Coordination polymer (CP) glasses have recently emerged as a new glass state. Given the young state of the field, the discovery of concepts that guide the synthesis of CP glasses with targeted thermal and macroscopic properties is at the center of ongoing research. In our work, we draw inspiration from research on inorganic glasses, investigating the impact of Li(C2N3) as a modifier on the thermal properties of the new molecular perovskite [(C3H7)3N(C4H9)]Mn(C2N3)3 (with [C2N3]− = dicyanamide, DCA). We derive the phase diagram and show that Li(C2N3) and [(C3H7)3N(C4H9)]Mn(C2N3)3 form a eutectic mixture, in which the melting temperature is decreased by 30 K. Additionally, for the eutectic mixture at xLiDCA ≈ 0.4, a CP glass forms under slow cooling, opening interesting pathways for scalable synthesis routes of CP glasses. Given the virtually unlimited parameter space of hybrid modifiers, they will play a major role in the future to alter the glass’ properties where the availability of rigorously derived phase diagrams will be important to identify material class overarching trends