Formation of glassy phases and polymorphism in deep eutectic solvents

Recently, there has been an increasing interest in the electrodeposition of various metals from deep eutectic solvents (DESs) as an alternative to other non-aqueous electrolytes. Beneficial characteristics include low viscosity compared to ionic liquids, a broad electrochemical stability window, and the individual components can be purified separately.[1] DESs consist of two components, an organic (type III) or inorganic (type IV) salt and a hydrogen bond donor (HBD).[2,3] If mixed in their eutectic ratio, a liquid is typically formed at room temperature and the freezing-point depression is believed to result from strong interactions between salt and HBD. However, the effect of the different components on this phenomenon has not been studied in detail, yet.In this study, the impact of various HBDs on the thermal properties is investigated as a function of their molar ratio in relation to the salt. Phase diagrams of DESs types III and IV are generated by differential scanning calorimetry (DSC), and subsequently, the eutectic composition and temperature of the respective mixtures are determined. As copper electrodeposition onto Au(111) single crystal electrodes has already been subject of numerous studies,[4,5] in this work it has been chosen as reference system to investigate the electrochemical characteristics of DESs by cyclic voltammetry, chronoamperometry, and electrochemical quartz crystal microbalance (EQCM). The impact of the salt, the HBD, and their molar ratio on Cu underpotential and bulk deposition and dissolution behavior are studied. We find that these reactions cannot be associated with the freezing-point depression of the DESs, but are instead strongly dependent on the electrolyte composition.The mechanism of Cu electrodeposition from chloride- and nitrate-containing DESs type III in combination with Cu+ and Cu2+ salts is affected by the high concentration of ions. Regardless of whether ethylene glycol or trifluoroacetamide is used as HBD, both Cu+ and Cu2+ species are easily reduced and deposited. The two-electron reduction prevails with presence of ethylene glycol and higher salt content. In all media studied, deposition follows a nucleation and three-dimensional growth mechanism controlled by diffusion. The diffusion rate of the Cu species is strongly related to the molar ratio of salt and HBD.DESs type IV exhibit a different behavior during electrodeposition and dissolution that is attributed to the HBD containing various functional groups. The HBD also influences the morphology of Cu deposits, as studied by atomic force microscopy (AFM). The crucial role of the anion is demonstrated in the examples of triflate and nitrate.

Transformation kinetics of the metastable bcc phase during rapid solidification of undercooled Fe-Co alloy melts

Knowledge of solid–liquid equilibria (SLE) and vapor–liquid equilibria (VLE) for mixtures containing deep eutectic solvents (DESs) is of paramount importance. We have conducted experiments to obtain additional data for SLE systems and then used the e-NRTL model to predict the VLE behavior in mixtures of DESs comprised of choline chloride (ChCl), sorbitol (S), and water (W). The systems under investigation include three 2-component systems (S/W, ChCl/W, ChCl/S), and one 3-component system (DES/W) where the DES is obtained by mixing ChCl and S at a molar ratio of 1. Using the e-NRTL activity coefficient model, the adjusted binary interaction parameters of the proposed model are determined solely from the experimental SLE data obtained from this work and also those in the literature. There is an excellent agreement between the SLE solubility data and the e-NRTL results. The tuned model is then used to predict the bubble pressure in three aqueous systems (S/W, ChCl/W, and DES/W) with an overall AARD value of 2.21%. The excellent agreement between the experimental and predicted VLE data demonstrates the viability of the proposed thermodynamic modelling framework to represent the equilibrium systems containing DESs. The outcome from our study can be used to relate the SLE and VLE data without the need to perform experiments for both cases for the given system of interest. Compared to the VLE experiments, the SLE tests are much simpler and safer because there is little compressibility and the effect of pressure on solubility is minimal which makes it possible to conduct SLE tests at room conditions (at least for liquids with negligible non-ideality). Therefore, conducting the high-pressure VLE calculations without the need to perform VLE experiments and through SLE experimental data alone will be of practical significance.

The article investigates the influence of high cooling rates during quenching from the melt on the formation of metastable phases and the appearance of metastable equilibrium diagrams. It is shown that with increasing cooling rate, both an increase in the existence region of strongly supersaturated solid solutions and the formation of new metastable phases in binary Fe-P and Sb-Zn alloys are observed. Mechanisms of non-equilibrium crystallization during quenching from the melt are proposed, the influence of large supercooling under high cooling rate conditions on changes in the kinetics of occurring crystallization and the emerging competition during non-equilibrium crystallization of congruent and incongruent phases are demonstrated. The validity of the newly formed metastable phase in the Sb-Zn alloy is confirmed by the correctness of the dependencies of specific atomic volumes of equilibrium phases calculated using Vegard's approximation. The lattice parameters of the emerging stable and metastable phases in the alloys are calculated.

Metastable phase formation in undercooled eutectic Ni78.6Si21.4 melts

The ability to model salt-containing deep eutectic solvents (DES) is essential for their rational design and application. Most existing thermodynamic models treat salts as neutral species, neglecting ionic interactions. This work investigates the explicit inclusion of ionic effects in modeling the liquid-phase nonideality of the binary choline chloride (ChCl)/water system. Experimental vapor–liquid equilibrium, solid–liquid equilibrium, water activity, and ChCl activity coefficients obtained from isopiestic measurements were used. Short-range molecular interactions were described with the nonrandom two-liquid (NRTL) model, while long-range ionic interactions were incorporated through the Pitzer–Debye–Hückel (PDH) term. Treating ChCl as a fully dissociated electrolyte and including the PDH contribution significantly improved the representation of nonideality across low and high salt concentrations. These results demonstrate the importance of electrolyte-based modeling frameworks for the development, optimization, and recycling of water-containing DES Types II–IV.

The present study reports the result of the measurement and analysis of the solubility curve and tie-line data of four ternary systems containing heptane–isopropyl alcohol azeotrope mixtures and deep eutectic solvents (DESs) at T = 298.2 K and p = 0.1 MPa. This investigation is aimed to evaluate the efficiency of the prepared DESs as extractants in the separation of the heptane–alcohol azeotropic mixtures through liquid–liquid extraction (LLE) processes. In this study, four choline chloride-based DESs were prepared by a heating process. Two hydrogen bond donor (HBD) compounds (i.e., ethylene glycol and propylene glycol) were chosen in the preparation of the DESs. The solubility curves show that the effect of DESs on the immiscibility region is small. The studied systems display the type-1 LLE behavior. The measured tie-line values were adequately fitted through the nonrandom two-liquid (NRTL) thermodynamic model, and the interaction parameter values were determined. The correlation data appeared to be in good agreement with the measured tie-lie data. The extraction capacity (distribution constants and selectivities) of the studied DESs was determined. The DESs had high and similar selectivity values for the studied systems. Moreover, the distribution constants were larger than unity, indicating a favorable solvent-to-feed ratio.

Separation of aromatics from aliphatics is challenging because of the close range of their boiling points and the formation of several combinations of azeotropes. Until now, no feasible separation process is available for aromatic concentrations below 20 wt%. In this work, we have investigated the possibility of using selected Deep Eutectic Solvents (DESs) for the liquid-liquid extraction of aromatics. DESs have emerged as green solvents that may offer several industrial alternatives. The DESs used in this work were synthesized from ammonium salt with ethylene glycol, lactic acid and sulfolane as Hydrogen Bond Donor (HBD). Equilibrium data for the ternary system consisting of ethylbenzene and n-octane with all DESs were measured at 25°C and atmospheric pressure. The results showed comparable distribution ratio and selectivity with commercial solvents. The absence of the HBD in the hydrocarbon layer, means the reduction of the number of separation stages. In addition, the Non-Random Two Liquid (NRTL) model was successfully used to correlate the experimental tie-lines and to calculate the phase compositions of the ternary systems.

Extractive desulfurization of fuels using diglycol based deep eutectic solvents

Phase selection during crystallization of undercooled liquid eutectic lead-tin alloys

Phase selection during solidification of undercooled Ni 70.2Si 29.8 eutectic alloy

Insights into phase evolution, foaming behavior and heavy metal immobilization in the oil-based cutting pyrolysis residues based lightweight building ceramsite production: The role of SiC

The thermal behavior of the hydrophobic eutectic mixtures formed by l-menthol (MEN) with 4-methoxyphenol (4-Met), 2-tert-butyl-4-methoxyphenol (BHA), 2-tert-butyl-4-ethylphenol (TBEP), and tert-butylhydroquinone (TBHQ) has been investigated to elucidate the different factors governing the solid–liquid equilibrium (SLE) at the molecular level. Our comparative study highlights the contribution of hydrogen-bonding (H-bonding) asymmetry of deep eutectic solvent (DES) precursors, i.e., their ability to act as strong H-bond donors and weak H-bond acceptors or vice versa. When deriving from resonance effects, this concept was previously presented as “polarity asymmetry” and introduced to explain the thermal behavior of type V DES. Here, we expand this concept to demonstrate that steric factors led by the insertion of ad hoc functional groups in the precursor molecules also have a dominant role in the deviation from thermodynamic ideality. In this way, an increasing temperature depression is observed starting from the 4-Met/MEN mixtures up to the BHA/MEN, TBHQ/MEN, and TBEP/MEN ones. The SLE prediction has been carried out through an innovative approach combining the COSMO-RS solvation model and density functional tight-binding molecular dynamics simulations, benchmarked against experimental data, and presented here for the first time. The impact of this work is that of providing new tools for a more conscious understanding and design of hydrophobic type V DES as new sustainable media for applicative purposes.

Deep eutectic solvent (DES) has demonstrated its ability to improve the yield and selectivity in the 5-hydroxymethylfurfural (HMF) production process. Liquid–liquid extraction is a beneficial process in HMF production to recover HMF from the reaction medium. In the present study, the effect of DES (choline chloride urea) on the liquid–liquid equilibria (LLE) of HMF–water–organic solvent (methyl isobutyl ketone (MIBK) or 2-pentanol) systems in the absence and presence of sodium chloride (NaCl) was investigated at 313.15 K and atmospheric pressure (0.1 MPa). The tie-lines of the multicomponent systems were measured using several analytical methods. According to the experimental results, the extraction performance decreased with an increase in DES concentration. However, the addition of 10 wt % NaCl into the HMF aqueous DES solution can induce stronger liquid–liquid phase splitting, enhancing the separation factors and distribution coefficients of HMF by around 2.7 and 1.6 times, respectively. Additionally, MIBK showed better extraction performance in the presence of DES and NaCl with the separation factors 2.6 times higher than those of 2-pentanol and the HMF distribution coefficients above 1.8. The LLE of the multicomponent systems were correlated well with the nonrandom two-liquid (NRTL) model.

Given the recent boom of applications for deep eutectic solvents (DES), there is a need for robust and accurate thermodynamic models that are able to describe them. Recent works have used molecular-based equations of state, derived from the Statistical Associating Fluid Theory (SAFT), to model DES due to their ability to explicitly account for hydrogen bonding, which is thought to govern the formation of a DES. However, the application of these association models to DES is a non-trivial task, because pure fluid data for several DES precursors are not available to be used in the model parameterization. The alternative parameterization procedures currently employed have evident flaws including the use of oversimplified association schemes, lack of transferability, inability to provide fundamental solid-liquid equilibrium data, and an overall poor accuracy. This work highlights the disadvantages of the current approaches while providing a novel methodology for the development of coarse-grained models applicable to DES. By proposing a more realistic association scheme and regressing the model parameters from experimental data that can be easily measured for a representative DES, a new coarse-grained model for [Ch]Cl, the most used DES precursor, was developed for soft-SAFT. The good performance and versatility of the new model were then successfully demonstrated through the modelling of a wide variety of [Ch]Cl-based DES, providing accurate descriptions of densities, vapor-liquid equilibria and solid-liquid equilibria data, for both binary and ternary systems. Furthermore, the novel approach can easily be applied to other SAFT-type models and extended to other solid DES precursors such as urea.