Solvent Exchange Process Research Articles

Microfluidic formation of surface nanodroplets using green deep eutectic solvents for liquid–liquid nanoextraction and controlled precipitation

HypothesisSurface nanodroplets have recently been employed for in situ chemical analysis leveraging their low volume, e.g. O(10−15 L), that enables rapid analyte extraction and pre-concentration. So far, most surface nanodroplets have been formed using single organic solvents such as 1-octanol, toluene, among others. Designing multicomponent surface nanodroplet with controllable composition is highly desirable for extending their application as extractant. ExperimentHere, we formed surface nanodroplets using green deep eutectic solvent (gDES) composed of thymol and decanoic acid, both of which are naturally occurring chemicals. The influence of parameters such as flowrate and the composition of deep eutectic solvent on the surface nanodroplet formation were studied. As proof-of-concept, the gDES surface nanodroplets were further used to extract and detect trace amounts of fluorescent rhodamine 6G dye and copper ions from water. FindingsThe formation of gDES surface nanodroplets follows the theoretical model which states that the final droplet volume (Vf) scales with the Peclét number (Pe) of the flow during formation by the solvent exchange process, that is Vf ∼ Pe3/4, and the nanodroplets demonstrate excellent ability as extractant for rhodamine 6G and copper ions from water. Surprisingly, the confined volume of gDES surface nanodroplets enables fast and controlled formation of Cu (II)-decanoate crystal.

Enhanced photocatalytic degradation of organic contaminants in water by highly tunable surface microlenses

Photocatalysis is one of the dominant technologies used to enhance the efficiency of water decontamination with light-based treatments. However, the effectiveness of photocatalysts is usually limited by the irradiation conditions and the properties of the water matrix. In this work, we have demonstrated the capability of surface microlenses (MLs) as a clean technology for more efficient photocatalytic water decontamination. Random or ordered surface MLs were fabricated from simple polymerization of nanodroplets produced in a solvent exchange process. Both random microlenses (MLR) and microlenses array (MLA) could enhance the photocatalytic degradation efficiency (η) of four representative organic pollutants, including methyl orange (MO), norfloxacin (NFX), sulfadiazine (SFD), sulfamethoxazole (SMX), spiked in ultra-pure water, synthetic natural water, or real river water. By controlling the conditions of light treatment, η could be enhanced by up to 402%. The effectiveness of surface MLs was validated under both visible LED light and simulated solar light and for two photocatalysts zinc oxide (ZnO) and titanium dioxide (TiO2). By reducing the concentration of the photocatalysts from 100 to 5 mg/L and the intensity of irradiation intensity from 1 Sun to 0.3 Sun, our findings suggest that the enhancement factor by MLs was higher at lower catalyst concentration, or at lower light intensity. Based on optical simulations and experimental results, we demonstrated that surface MLs optimize the light distribution and promote the formation of active species, which results in the enhancement of η. The use of MLs may serve as a novel strategy to improve the photocatalytic degradation of micropollutants, especially in places where the available light source is weak, such as indoors or in cloudy regions.Synopsis: MLs-enhanced photocatalysis degradation of organic contaminants in different water matrices.

Synthesis of Low Density and High Purity Silica Xerogels from South African Sugarcane Leaves without the Usage of a Surfactant

Sugarcane leaves were used to produce high-purity and low-density silica xerogels through a sol–gel method. The biogenic silica produced through a thermochemical method was reacted with sodium hydroxide (NaOH) to form sodium silicate and the produced sodium silicate was titrated with 1 M citric acid to form silica gel. The formed silica gel was washed, subjected to a solvent exchange process and later dried at 80 °C to produce low-density and high-purity silica xerogels. The produced xerogels were characterized with energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), nitrogen physisorption, elemental analysis (CHNS), X-ray fluorescence (XRF), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The produced silica xerogels had an amorphous structure and purity of 99.9 wt%. In addition, the textural properties analysis showed that the xerogel has a BET surface area of 668 m2·g−1, an average pore diameter of 7.5 nm, a pore volume of 1.26 cm3·g−1 and a density of 0.23 g·cm−3.

Graphene Oxide Based Transparent Resins For Accurate 3D Printing of Conductive Materials

AbstractDigital Light Processing (DLP) allows the fast realization of 3D objects with high spatial resolution. However, DLP is limited to transparent resins, and therefore not well suited for printing electrically conductive materials. Manufacturing conductive materials will significantly broaden the spectrum of applications of the DLP technology. But conductive metals or carbon‐based fillers absorb and scatter light; inhibiting thereby photopolymerization, and lowering resolution. In this study, UV transparent liquid crystal graphene oxide (GO) is used as precursor for generating in situ conductive particles. The GO materials are added to a photopolymerizable resin via an original solvent exchange process. By contrast to earlier contributions, the absence of drying during the all process allows the GO material to be transferred as monolayers to limit UV scattering. The absence of UV scattering and absorption allows for fast and high‐resolution 3D printing. The chosen resin sustain high temperature to enable an in situ efficient thermal reduction of GO into reduced graphene oxide (rGO) that is electrically conductive. The rGO particles form percolated networks with conductivities up to 1.2 × 10−2 S m−1. The present method appears therefore as a way to reconcile the DLP technology with the manufacturing of 3D electrically conductive objects.

Membrane-Based Solvent Exchange Process for Purification of API Crystal Suspensions.

Bottom-up approaches to producing aqueous crystal suspensions of active pharmaceutical ingredients (APIs), such as anti-solvent crystallisation, are gaining interest as they offer better control over surface properties compared to top-down approaches. However, one of the major challenges that needs to be addressed is the removal of organic solvents after the crystallisation step due to strict limitations regarding human exposure. Within this work, we investigated a process concept for the removal of solvent (i.e., ethanol) from the API crystal suspension using membrane-based diafiltration. A four-stage diafiltration process successfully reduced the ethanol concentration in the API (here, naproxen) crystal suspension below 0.5 wt% (the residual solvent limit as per ICH guidelines) with a water consumption of 1.5 g of added water per g of feed. The solvent exchange process had no negative influence on the stability of the crystals in suspension, as their size and polymorphic form remained unchanged. This work is a step towards the bottom-up production of API crystal suspension by applying solvent/anti-solvent crystallisation. It provides the proof of concept for establishing a process of organic solvent removal and offers an experimental framework to serve as the foundation for the design of experiments implementing a solvent exchange in API production processes.

Redox and guest tunable spin-crossover properties in a polymeric polyoxometalate.

A bifunctionalized polyoxometalate (POM), [V6O19(C16H15N6O)2]2-, which contains a redox active hexavanadate moiety covalently linked to two tridentate 2,6-bis(pyrazol-1-yl)pyridine (1-bpp) ligands, has been prepared and characterized. Reaction of this hybrid molecule with Fe(ii) or Zn(ii) ions produces crystalline neutral 1D networks of formula Fe[V6O19(C16H15N6O)2]·solv (2) and Zn[V6O19(C16H15N6O)2]·solv (3) (solv = solvent molecules). Magnetic properties of 2 show an abrupt spin-crossover (SCO) with the temperature, which can be induced by light irradiation at 10 K (Light-Induced Excited Spin-State Trapping, LIESST effect). Interestingly, this porous and flexible structure enables reversible exchange of solvents in 2, which allows tuning the temperature of the thermal SCO. In 2 and 3, the hexavanadate unit can be reduced by electrochemical or chemical means in a reversible way. Chemical reduction and reoxidation by a postsynthetic method is accompanied by the insertion in the structure of the reductant and oxidant molecules (cobaltocene and tribromide, respectively), which provokes drastic changes in the spin state of Fe(ii). This leads to an elegant switching multifunctional material in which SCO properties of the Fe(ii) complexes coexist with the redox properties of the POM and can be tuned by a variety of stimuli such as temperature, light, solvent exchange or electron transfer. During the reduction process, 3 undergoes a single-crystal-to-single-crystal one-electron reduction, which confirms the presence of cobaltocenium cations by single crystal X-ray diffraction.

Interfacial Instability-Induced (3I) Adhesives through "Mediator" Solvent Diffusion for Robust Underoil Adhesion.

Underoil adhesives are intensively needed in case of oil spill caused by pipeline rupture, but remain a challenge owing to the obstruction of oil layer or their swelling in oil. Herein, a general solvent diffusion principle is demonstrated by introducing dual-soluble "mediator" solvents to develop a new type of interfacial instability-induced (3I) adhesives, achieving effective underoil adhesion on various substrates and blocking the oil leakage within seconds. Microscopic characterization reveals a fast and dynamic solvent exchange process that destroys the oil layer by liquid-liquid interfacial diffusion between the "mediator" solvent and oil, enabling 3I adhesives to contact the solid surfaces directly. The principle of interfacial instability-induced liquid replacement is quite different from typical immiscible liquid replacement and is not restricted by the surface tension of solvents, surface energy, and roughness of solid surfaces, successfully directing the construction of a series of effective 3I adhesives with commercially available feedstocks. This study provides a unique clue for the design of next-generation adhesives in complex environments.

Phase Separation–Controlled Assembly of Hierarchically Porous Aramid Nanofiber Films for High‐speed Lithium‐Metal Batteries (Small 52/2022)

Porous Aramid Nanofiber Films In article number 2205355, Jeong Gon Son, Bongjun Yeom, and co-workers report highly porous aramid nanofiber separators with dual porosity (>97%), prepared by a two-step solvent exchange process, for Lithium-metal batteries. The hierarchical porous structure with maximized porosity and selective affinity of the aramid nanofibers to anions shows effectively reduced Li dendrite formation and stable cycling performance under high-speed charge/discharge conditions.

Phase Separation-Controlled Assembly of Hierarchically Porous Aramid Nanofiber Films for High-speed Lithium-Metal Batteries.

The growth of lithium (Li) dendrites reduces the lifespan of Li-metal batteries and causes safety issues. Herein, hierarchically porous aramid nanofiber separators capable of effectively suppressing the Li dendrite growth while maintaining highly stable cycle performances at high charge/discharge rates are reported. A two-step solvent exchange process combined with reprotonation-mediated self-assembly is utilized to control the bimodal porous structure of the separators. In particular, when ethanol and water are used sequentially, aramid nanofibers form hierarchical porous structures containing nanopores in macroporous polymer frameworks to yield a mechanically robust membrane with high porosity of 97% or more. The optimized samples exhibit high ionic conductivities of 1.87-4.04 mS cm-1 and high Li-ion transference numbers of 0.77-0.84 because of the ultrahigh porosity and selective affinity to anions. Li-metal symmetric cells do not show any noticeable presence of dendrites after 100 cycles, and they operate stably for more than 1500 cycles even under extreme conditions with a high current density of >20 mA cm-2 . In addition, the LiFePO4 /Li full cell retains 86.3% of its capacity after 1000 cycles at a charge rate of 30 C.

Time-Dependent Development of Mesoporosity in Ionic Liquid Treated Cellulosic Materials

Natural Fiber Welding (NFW) is process that leverages the unique solvating power of ionic liquids (IL) to mobilize a natural fiber’s outermost polymer strands and enable these mobile polymers to reconfigure and interact with mobilized polymers of adjacent fibers. Upon removal of the ionic liquid via a solvent exchange and drying process, the biopolymer material is welded into a new matrix while still maintaining the vast majority of its native structural hierarchy. Recent work in our laboratory has shown relatively simple modifications to the NFW process can drastically impact the modified matrix morphology, particularly regarding surface structure. Changes in polarity during the solvent exchange process, for instance, can be used to very the surface area over a 1000-fold and produce high surface are materials with tunable mesoporosity. In the present work we investigate the impact of variable ionic liquid treatment time on the development of mesoporosity in fiber welded cotton substrates. Nitrogen gas adsorption/desorption measurements were employed to evaluate changes in surface area and pore size with ionic liquid treatment time. Raman spectroscopy was carried out on epoxy potted material cross sections to assess the impact of treatment time on cellulose decrystallization, and epoxy penetration measured by Raman spectroscopy was used to evaluate the continuity of the mesoporous regions and further asses material porosity.

Asphaltene precipitation under controlled mixing conditions in a microchamber

Solvent exchange is a controlled process for dilution-induced phase separation. This work utilizes the solvent exchange method to reveal the effect of the mixing dynamics on the asphaltene precipitation process under 20 different mixing conditions using a model system of n-heptane and asphaltene in toluene. The external mixing between the asphaltene solution and the paraffinic solvent is strictly controlled. We employed high-spatial resolution total internal reflection fluorescence microscope to detect asphaltene precipitates with a resolution up to ∼ 200 nm. A multiphysics model is used to simulate the evolution of oversaturation pulse in the solvent exchange process. Based on the simulation results, we predicted the effect of the flow rate, dimension, orientation of the microfluidic chamber, and temperature on the surface coverage and size distribution of asphaltene precipitates. The model predictions of all factors corroborate with the experimental observations. Local concentration of the solvent and shear forces are found to be the two main reasons for the change of asphaltene precipitation caused by mixing dynamics. However, the influence of thermodynamics is more critical than the mixing dynamics as temperature changes. Through a combination of experimental and simulation studies, this work illuminates the significance of the transportation process for the final morphology of asphaltene precipitates and provides a in-depth insight into the mechanism of mixing dynamics on the asphaltene precipitation. A smart mixing may be to boost new phase formation without excessive solvent consumption.

Nanobowls from Amphiphilic Core–Shell Cyclic Bottlebrush Polymers

Cyclic bottlebrush polymers are macrocycles that contain pendent side-chain polymers on nearly every repeat unit. We leveraged a method to generate cyclic bottlebrush polymers utilizing ring-expansion polymerization (REP) followed by subsequent grafting-from via atom-transfer radical polymerization (ATRP) to produce core–shell cyclic bottlebrush polymers and investigated their self-assembly behavior in water. The bottlebrush polymers were comprised of a cyclic backbone with side chains composed of a hydrophobic polystyrene block and a hydrophilic poly(acrylic acid) block. A two-step morphological transformation from spheres to porous spheres to nanobowls (spheres with a single large pore) was observed with solvent exchange from tetrahydrofuran to water. In contrast, under identical experimental conditions, an analogous linear bottlebrush polymer with a similar backbone and side chain degrees of polymerizations did not aggregate into nanobowls but rather exhibited a porous sphere morphology. These unusual morphologies and their propensities to transform can be attributed to changes in the internal viscosity of the aggregates during the solvent exchange process. Additionally, the rate of solvent exchange was found to influence the propensity for shape transformation to occur.

Micro-droplet nucleation through solvent exchange in a turbulent buoyant jet

Solvent exchange is a process involving mixing between a good solvent with dissolved solute and a poor solvent. The process creates local oversaturation which causes the nucleation of minute solute droplets. Such ternary systems on a macro-scale have remained unexplored in the turbulent regime. We experimentally study the solvent exchange process by injecting mixtures of ethanol and trans-anethole into water, forming a turbulent buoyant jet in the upward direction. Locally, turbulent mixing causes oversaturation of the trans-anethole following turbulent entrainment. We optically measure the concentration of the nucleated droplets using a light attenuation technique and find that the radial concentration profile has a sub-Gaussian kurtosis. In contrast to the entrainment-based models, the spatial evolution of the oversaturation reveals continuous droplet nucleation downstream and radially across the jet, which we attribute to the limited mixing capacity of the jet. Although we are far from a full quantitative understanding, this work extends the knowledge on solvent exchange into the turbulent regime, and brings in a novel type of flow, broadening the scope of multicomponent, multiphase turbulent jets with phase transition.

Ultrafast, highly sensitive, flexible textile-based humidity sensors made of nanocomposite filaments

Wearable electronics are promising next-generation smart textiles for human-computer interaction, health monitoring, and other applications. However, integrating electronic functions into strong, highly deformable electronic textiles and maintaining their functionalities during wear is a great challenge. Herein, we report ultrafast, highly sensitive, textile-based humidity sensors made of single-walled carbon nanotube (SWNT)/polyvinyl alcohol (PVA)/lithium chloride (LiCl) nanocomposite filaments fabricated via a wet-spinning and a solvent exchange process. The SWNT/PVA/LiCl textile-based humidity sensors exhibited excellent stabilities during deformation and high sensitivities with 6-fold resistance variations over a wide range of relative humidity (RH) conditions. The ultrafast responses of the sensors were attributed to the quick deliquescence of LiCl during contact with water molecules and the simultaneous conductivity change caused by the generated ions. The as-prepared sensors responded well to human breathing and real-time humidity changing, which could distinguish different breaths and microclimate changes. Such outstanding sensing performances of our textile-based sensors, in combination with their mechanical flexibilities, enable the facile integration of high-performance humidity sensors onto textile substrates for real-time microclimate monitoring.

Turning the morphology and wetting ability of self-assembled hierarchical structures from lignin stearoyl esters

Well-organized and self-assembled structures with hierarchical surface architectures have recently attracted considerable attention due to their potentially wide application range. Herein, remarkable lignin-based petaloid nanoflakes (LPNFs) were formed via the crystallization of polymeric lignin stearoyl esters (LSEs). A solvent exchange self-assembly technique using Tetrahydrofuran (THF) as a solvent in addition to ethanol, acetone, and water as nonsolvents was used to form LPNFs by the crystallization of the stearyl groups in LSEs during evaporation. The grafting level of the stearoyl groups in the LSEs, the difference of the nonsolvent, and the volume ratios of the solvent/nonsolvent during the solvent exchange process predominantly determined the formation of LPNFs via this process. The self-assembled structures could be constructed as spherical particles and as constituted LPNFs structures with well-organized petaloid nanoflakes. By introducing sufficient amounts of LPNFs patterns on the substrates (e.g., glass slide, paper, and wood), the hydrophilic substrates were successfully transformed into superhydrophobic surfaces. Thus, the synthesis of LSEs and the formation of LPNFs with tunable structures offer a new strategy for the derivation and value-added utilization of lignin.

Solvent exchange-induced facile recrystallisation and particle size control of sulphide solid electrolytes for all-solid-state Li-ion batteries

A size-controlled high-quality sulphide solid electrolyte for all-solid-state Li batteries was prepared by a novel polar-to-nonpolar solvent exchange process.

Hollow Graphene Fibers with Archimedean-Type Spirals for Flexible and Wearable Electronics

Graphene fiber (GF) processes attract prospects for flexible and wearable electronic applications by virtue of their excellent electrical conductivity, flexibility, strength, and being lightweight. Herein, we reported a facile method of fabricating hollow GFs with Archimedean-type spirals via a self-curing process induced from the counter-acting force of evaporation along a parabolic cross section. This strategy can boost the production rate up to 771.4 m h–1 by printing the graphene oxide (GO) dispersion onto a rotating roller and then immersing in ethanol with the roller instead of injecting that into the coagulation bath directly, breaking through the rate limitation of the solidification in the conventional wet-spinning method. The 3D printing process on the rotating roller can not only transfer the ejecting dispersion continuously to form gel fiber but also provide a unilateral support to compress the fiber in the radial direction to a compacted layer structure during the solvent exchange process. Meanwhile, a series of such kinds of fibers with various diameters can be efficiently obtained by adjusting critical fabricating parameters of the injecting rate and the rotating rate. The as-fabricated pristine hollow GFs showed a reasonable tensile strength of 190.5 MPa with 6.1% elongation strain and good durability for bending over 5000 cycles. The demonstrative supercapacitor with the GF exhibited a high specific capacitance of 170.6 F g–1. With the specific structure and reasonable performances, the hollow GFs hold great potential application to flexible and wearable electronics like stretchable circuitries, sensors, flexible batteries, and wearable supercapacitors.

Partial Order–Disorder Transformation of Interpenetrated Porous Coordination Polymers

Controlling interpenetration and flexibility behaviors is intriguing and fundamental for porous coordination polymers. We report exceptional interpenetration behaviors involving controllable partia...

Novel Flyweight Three-Dimensional Self-Assembled Graphene Oxide/Octa(Aminophenyl) Polyhedral Oligomeric Silsesquioxane Hybrid Aerogels

Herein, flyweight organic-inorganic hybrid scaffolds were fabricated by self-assembly and reduction of graphene oxide via covalent reaction of octa(aminophenyl) polyhedral oligomeric silsesquioxane with graphene oxide. Octa(aminophenyl) polyhedral oligomeric silsesquioxane created a decorative coating on the graphene oxide surface. It acts as a nano-crosslinker, especially on the overlapped-zone of graphene oxide platelets to bind them close-fitting. The resulting hybrid hydrogel was transformed into aerogel by the solvent exchange process with liquid carbon dioxide, followed by liquid carbon dioxide supercritical drying. Different concentrations of graphene oxide and octa(aminophenyl) polyhedral oligomeric silsesquioxane were prepared and the structure-property relationship of obtained aerogels is elucidated. The bulk density and porosity of the aerogels are located between the super-low values of 2.7 to 5.9 mg cm-3 and beyond 99.5 %, respectively. According to the adsorption-desorption isotherms of BET-technique, the surface area of obtained aerogels was between 250 to 713 m2/g. The findings remark the potential application of obtained aerogels in the production of supercapacitors, lithium-ion batteries, solar cells, etc. in energy storage and conversion devices, electrode materials, sensors, gas/oil/dye adsorbents, and high-temperature insulators in the aerospace industry.

Performance regulation of silica aerogel powder synthesized by a two-step Sol-gel process with a fast ambient pressure drying route

This paper proposed a timesaving route for preparing silica aerogel powder with TEOS as a precursor. Thermal insulating super hydrophobic silica aerogel powder was synthesized by combining two-step Sol-gel reaction with a fast ambient pressure drying process. Silica Sol-gel was formed after catalytic reaction by oxalic acid and NH4OH, and then turned to be hydrophobic aerogel through further surface modification (only three hours with no solvent exchange process) and drying process. By optimizing every tiny trace of synthetic component, the obtained silica aerogel powder exhibits excellent properties, such as low apparent density (0.212 g/cm3) and thermal conductivity (0.053 W/mK), as well as high BET surface area (769.86 m2/g) and water contact angle (149.0 °). This work presents a timesaving method for synthesizing thermal insulating hydrophobic silica aerogel powder.