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Deep eutectic solvents have emerged in green chemistry only seventeen years ago and yet resulted in a plethora of publications covering various research areas and diverse fields of application. Deep eutectic solvents appear as promising alternatives to conventional organic solvents due to their straightforward preparation using highly accessible and natural compounds. They display also high tunability. Here we present the classification and preparation methods of deep eutectic solvents. We detail their physicochemical properties such as phase behavior, density, viscosity, ionic conductivity, surface tension, and polarity. Properties are controlled by the choice of the forming compounds, molar ratio, temperature, and water content.

The L ↔ Al + Al11Ce3 technologically important eutectic transformation in Al–Ce binary alloys, containing from 5 to 20 wt.% Ce and ranging from hypo- to hypereutectic compositions, was examined along with the microstructure and properties of its solidified product. A combination of thermal analysis and metallography determined the coordinates of the eutectic point at 644.5 ± 0.6 °C and 10.6 wt.% Ce, clarifying the existing literature ambiguity. Despite the high entropy of melting of the Al11Ce3 phase, in hypoeutectic alloys the eutectic was dominated by the regular morphology of periodically arranged lamellae, typical for non-faceted systems. In the lamellar eutectic, however, the faceting of Al11Ce3 was identified at the atomic scale. In contrast, for hypereutectic compositions, the Al11Ce3 eutectic phase exhibited complex morphology, influenced by the proeutectic Al11Ce3 phase. The Al11Ce3 eutectic phase lost its coherency with Al; it was deduced that a partial coherency was present only at early stages of lamellae growth. The orientation relationships between the Al11Ce3 and Al in the eutectic structure, leading to partial coherency, were determined to be [0 0 1]Al ║ [1¯ 1 1]Al11Ce3 with (0 4 4¯)Al ║ (2¯ 0 0)Al11Ce3 and [0 1 1]Al ║ [3¯ 0 1]Al11Ce3 with (2¯ 0 0)Al ║ (0 6 0)Al11Ce3. The Al11Ce3 phase with a hardness of 350 HV and Al matrix having 35 HV in their eutectic arrangement formed in situ composite, with the former playing a role of reinforcement. However, the coarse and mostly incoherent Al11Ce3 eutectic phase provided limited strengthening and the Al–Ce alloy consisting of 100% eutectic reached at room temperature a yield stress of just about 70 MPa.

The increasing antibiotic resistance towards a panel of microorganisms is one of the public health concerns. For this reason, the search for alternatives to the widely used antibiotic has been undertaken. In the era of sustainable chemistry, deep eutectic solvents (DESs) have emerged as promising antimicrobial agents. These solvents possess several advantages such as low volatility, low flammability, ease of preparation, and typically low cost of production. These properties make DES suitable for various applications, including extraction of biomolecules and preparation of cosmetics. Natural DESs (NADESs) are special category of DESs prepared from natural sources, which matched the recent trends of leaning back to nature, and decreasing dependence on synthetic precursors. NADES can be prepared by heating and stirring, freeze-drying, evaporation, grinding, and ultrasound-assisted and microwave-assisted synthesis. Utilizing NADESs as an alternative to traditional antibiotics, which become ineffective over time due to bacterial resistance, holds great promise for these reasons. This review aims to discuss the antimicrobial properties of multiple NADESs, including antibacterial and antifungal activities. To the best of our knowledge, this review is the first literature survey of the antimicrobial activities of NADESs. Key points • Natural deep eutectic solvents are promising antimicrobial alternative to antibiotics • NADES holds high potential for their activity against bacterial resistance • NADES have also substantial antifungal activities

Natural gels and biomimetic hydrogel materials have been able to achieve outstanding integrated mechanical properties due to the gain of natural biological structures. However, nearly every natural biological structure relies on water as solvents or carriers, which limits the possibility in extreme conditions, such as sub-zero temperatures and long-term application. Here, peptide-enhanced eutectic gels were synthesized by introducing α-helical “molecular spring” structure into deep eutectic solvent. The gel takes full advantage of the α-helical structure, achieving high tensile/compression, good resilience, superior fracture toughness, excellent fatigue resistance and strong adhesion, while it also inherits the benefits of the deep eutectic solvent and solves the problems of solvent volatilization and freezing. This enables unprecedentedly long and stable sensing of human motion or mechanical movement. The electrical signal shows almost no drift even after 10,000 deformations for 29 hours or in the −20 °C to 80 °C temperature range. Biomimetic hydrogel materials show outstanding mechanical properties but water as solvent or carrier limits the possibility to apply these materials under extreme conditions. Here the authors report a peptide-enhanced eutectogel with excellent mechanical, anti-freezing and anti-drying properties and its application as sensor for monitoring human motion.

A series of CoCrFeNiMox (x = 0.2, 0.4, 0.6, 0.8, 1.0, and 1.2) high-entropy alloys were designed to develop a eutectic high-entropy alloy system and to acquire a superfine eutectic structure. The results show that for the CoCrFeNiMox alloys, with the increase of Mo content from 0.2 to 1.2, the microstructures shift from a typical dendrite structure to a hypoeutectic microstructure (x = 0.6), and then to a fully eutectic microstructure (x = 0.8) with a lamellar spacing only 110 nm, and finally culminate in the hypereutectic structure (x = 1.0, x = 1.2). The XRD results show that CoCrFeNiMox alloys have a single FCC phase when x is 0.2 or 0.4. When Mo content is over 0.6, it begins to separate Cr9Mo21Ni20 intermetallic compounds. The hardness of the CoCrFeNiMox alloys is increasing significantly from 172.8 to 763.7 HV with the increase of Mo content. Meanwhile, the fracture strength increased but the ductility decreases. Among these alloys, the CoCrFeNiMo0.6 alloy shows excellent integrated mechanical properties of compressive fracture strength and strain, which are 2051 Mpa and 23%, respectively.

Conventional material processing approaches often achieve strengthening of materials at the cost of reduced ductility. Here, we show that high-pressure and high-temperature (HPHT) treatment can help overcome the strength-ductility trade-off in structural materials. We report an initially strong-yet-brittle eutectic high entropy alloy simultaneously doubling its strength to 1150 MPa and its tensile ductility to 36% after the HPHT treatment. Such strength-ductility synergy is attributed to the HPHT-induced formation of a hierarchically patterned microstructure with coherent interfaces, which promotes multiple deformation mechanisms, including dislocations, stacking faults, microbands and deformation twins, at multiple length scales. More importantly, the HPHT-induced microstructure helps relieve stress concentration at the interfaces, thereby arresting interfacial cracking commonly observed in traditional eutectic high entropy alloys. These findings suggest a new direction of research in employing HPHT techniques to help develop next generation structural materials. Conventional material processing methods often suffer by strength-ductility trade-off. Here, the authors show high-pressure and high-temperature treatment can transform an eutectic high entropy alloy to having a hierarchical microstructure with simultaneous enhancements of strength and ductility.

Most of the traditional solvents for the preparation of CQDs are single solutions. In this study, four CQDs were prepared by a one-step solvothermal method using alkali lignin as the precursor carbon source, and four CQDs were prepared by a one-step solvothermal method using low-eutectic solvents of ChCl/FA (1:3), ChCl/LA (1:3), ChCl/MA (1:3), and ChCl/pTSA (1:1), and one CQD was prepared by a one-pot hydrothermal method in deionised water. The quantum yield of the CQDs prepared in the low-eutectic solvent system was much higher than that of the CQDs prepared by the conventional hydrothermal method. The carbon quantum dots prepared in a low eutectic solvent system were used for the detection of Fe3+ in the range of 0-250 μM with the detection limits of CQDs-FA (0.4 μM), CQDs-LA (4.34 μM), CQDs-MA (5.23 μM), and CQDs-pTSA (1.72 μM), respectively.

‘Ideal’ solvents in biocatalysis have to fulfill a large number of requirements, such as high substrate solubility, high enzyme activity and stability, and positive effects on reaction equilibrium. In the past decades, many enzymatic synthesis routes in water-based and nonaqueous (organic solvents, ionic or supercritical fluids) reaction media have been developed. However, no solvent meets every demand for different reaction types at the same time, and there is still a need for novel solvents suited for different reaction types and applications. Deep eutectic solvents (DESs) have recently been evaluated as solvents in different biocatalytic reactions. They can improve substrate supply, conversion, and stability. The best results were obtained when the DES is formed by the substrates of an enzymatic reaction. A wide range of inexpensive renewables can be used as components of deep eutectic solvents; therefore, the solvents are often biodegradable, nontoxic, nonvolatile, and nonflammable. A broad range of enzymatic and chemo-enzymatic synthesis reactions can be performed in deep eutectic solvents. Most of the reactions, covering transesterifications, epoxidations, and C–C bond formations, are catalyzed by lipases. Deep eutectic solvents can be used to enable new biocatalytic synthesis routes that cannot be realized in conventional reaction media (i.e., aqueous buffers). Components of deep eutectic solvents can be used as substrate and solvent at the same time; this virtually solvent-free approach enables processes with high substrate conversion and high atom efficiency.

The microstructure of hypereutectic Al-Si alloys is crucial in determining their mechanical properties and overall performance in engineering applications. This paper investigates the effect of a rotating magnetic field (RMF) and eutectic front velocity on the microstructure of hypereutectic Al-18 wt.% Si alloy. The hypereutectic samples were solidified using five different front velocities (0.02, 0.05, 0.09, 0.2, and 0.4 mm/s) with an average temperature gradient (G) of 8 K/mm in a crystallizer equipped with an RMF inductor. The samples were solidified into two sections. The first section solidified without stirring, while the second section solidified with stirring using RMF at an induction (B) of 7.2 mT. The length, angular orientation of eutectic Si lamellas, and interlamellar distances were measured in both the non-stirred and the stirred sections to evaluate the impact of RMF and front velocity on the eutectic structure. The results revealed that the application of RMF and the increase in front velocity during solidification led to the significant refinement of the eutectic structure. These findings highlight the potential of RMF and front velocity manipulation to enhance the microstructure of hypereutectic Al-Si alloys, with practical implications for the development of high-performance materials.

A specific eutectic (Cr,Fe)-(Cr,Fe)23C6 structure had been previously reported in the research studies of Fe-Cr-C hardfacing alloys. In this study, a close observation and discussion of the eutectic (Cr,Fe)-(Cr,Fe)23C6 were conducted. The eutectic solidification occurred when the chromium content of the alloy exceeded 35 wt pct. The eutectic structure showed a triaxial radial fishbone structure which was the so called \"complex regular structure.\" Lamellar costa plates showed local asymmetry at two sides of a spine. Individual costae were able to combine as one, and spines showed extra branches. Costae that were nearly parallel to the heat flow direction were longer than those that were vertical to the heat flow direction. The triaxial spines preferred to intersect at 120 deg, while the costae preferred to intersect the spine at 90 deg and 35.26 deg due to the lattice relationships. The solidified metal near the fusion boundary showed an irregular structure instead of a complex regular structure. The reason for the irregular morphology was the high growth rate near the fusion boundary.