Recent Advances in the Synthesis of N-fluoroalkyl Amides/Sulfonamides and Their Carbonyl/Sulfonyl Derivatives.

Organofluorine compounds have consistently demonstrated practical applications in the life sciences due to the fascinating properties imparted by the fluorine substituents. In recent years, significant advancements have been made in the synthesis of N-fluoroalkyl carbonyl and sulfonyl compounds. This review offers a current overview of the various synthetic routes for N-fluoroalkyl amides/sulfonamides and their transformation to new unexplored N-fluoroalkyl carbonyl/sulfonyl derivatives, categorized into three parts based on the different fluoroalkyl groups.

Synthesis of Unsymmetrical Trisulfides from S-Substituted Sulphenylthiosulphates.

Trisulfide unit is widely found in natural products and has garnered attention due to the unique pharmacological and physiochemical properties. However, despite limited progress, widely applicable approaches for constructing unsymmetrical trisulfides have so far remain scarce. In this work, an easy-to-prepare, solid-state and scalable reagent, S-substituted sulphenylthiosulphate, has been developed for the divergent synthesis of unsymmetrical trisulfides. Alkyl electrophile substrates, including bromides, chlorides, iodides and tosylates, with diverse substituents are smoothly converted to the corresponding trisulfides with S-substituted sulphenylthiosulphates and thiourea as another sulfur source. Furthermore, the late-stage modification of drug molecules was successfully achieved through this method.

A Facile Single-Phase-Fluid-Driven Bubble Microfluidic Generator for Potential Detection of Viruses Suspended in Air.

Microfluidics devices have widely been employed to prepare monodispersed microbubbles/droplets, which have promising applications in biomedical engineering, biosensor detection, drug delivery, etc. However, the current reported microfluidic devices need to control at least two-phase fluids to make microbubbles/droplets. Additionally, it seems to be difficult to make monodispersed microbubbles from the ambient air using currently reported microfluidic structures. Here, we present a facile approach to making monodispersed microbubbles directly from the ambient air by driving single-phase fluid. The reported single-phase-fluid microfluidic (SPFM) device has a typical co-flow structure, while the adjacent space between the injection tube and the collection tube is open to the air. The flow condition inside the SPFM device was systematically studied. By adjusting the flow rate of the single-phase fluid, bubbles were generated, the sizes of which could be tuned precisely. This facile bubble generator may have significant potential as a detection sensor in detecting viruses in spread droplets or haze particles in ambient air.

Microfluidic Assembly of Microblocks into Interlocked Structures for Enhanced Strength and Toughness.

Compared with monolithic materials, topologically interlocked materials (TIMs) exhibit higher toughness based on their enhanced crack deflection and deformation tolerance. Importantly, by reducing the block size of TIMs, their structural strength can also be improved due to the reduced flexural span. However, the assembly of microscale blocks remains a huge challenge due to the inadequacy of nanoscale self-assembly or macroscale pick-and-place operations. In this work, octahedral microblocks are fabricated and constructed into interlocked structures with different patterns through microfluidic channels with variable cross sections. The pattern of the interlocked panel is demonstrated to affect its strength and toughness. The failure strength and energy absorption of assembled panels significantly exceed that of their monolithic counterpart by ∼33% and ∼19.1 folds, respectively. Generally, the presented microfluidic method provides a unique technique for the assembly of interlocked architecture, which facilitates the design and fabrication of TIMs with highly improved strength and toughness.

A Model of Stress-Damage-Permeability Relationship of Weakly Cemented Rocks under Triaxial Compressive Conditions.

To unravel the permeability variation mechanism of weakly cemented rocks (WCR), the paper conducted triaxial permeability tests on weakly cemented sandstones (WCS) collected from the Jurassic formation in northwest China. The paper identified the correlation of WCS permeability versus porosity, cementation structure, and mineral composition, further developing a model to characterize the WCS stress-damage-permeability relationship. The research indicated that the WCS permeability was initially high due to the naturally high porosity, large pore diameter, and loose particle cementation, thus favoring a significant decline as pore convergence in the compaction stage. In the residual stage, kaolinite and montmorillonite minerals disintegrated into water and narrowed fractures, causing a slight permeability increase from the initial to the maximum and residual stages. The WCS matrix fracturing was phenomenologically accompanied by clay mineral disintegration. By assuming that the matrix can be compressed, jointed, and fractured, the paper defined a damage variable D and accordingly developed a stress-damage-permeability relationship model that incorporated matrix compression, jointing, and fracturing. The model can describe the WCS permeability regime regarding the high initial permeability and slight difference of the maximum and residual permeabilities versus the initial.

Fabrication of sharp-edged 3D microparticles via folded PDMS microfluidic channels.

3D microparticles have promising applications in self-assembly, biomedical engineering, mechanical engineering, etc. The shape of microparticles plays a significant role in their functionalities. Although numerous investigations have been conducted to tailor the shape of microparticles, the diversity is still limited, and it remains a challenge to fabricate 3D microparticles with sharp edges. Here, we present a facile approach that combines a folded PDMS channel and orthogonal projection lithography for shaping sharp-edged 3D microparticles. By adjusting the number and the length of channel sides, both regular and irregular polyhedral cross-sections of the folded channel can be obtained. UV light with diverse patterns is applied vertically as the second shape controlling factor. A variety of 3D microparticles are obtained with sharp edges, which are potential templates for micromachining tools and abrasives. Some sharp-edged microparticles are assembled into 2D and 3D mesoscale structures, which demonstrates their prospective applications in self-assembly, tissue engineering, etc.

Determining the scale of coal mining in an ecologically fragile mining area under the constraint of water resources carrying capacity.

A reasonable mining scale is very important for the development of mining areas. In view of the lack of water resources in arid and semi-arid areas, this paper studies the scale of coal mining in arid and semi-arid areas under the constraint of the water resources carrying capacity (WRCC) with the aim of realizing the conservation mining of ecological environment. From the perspectives of market demand side, production side and the constraint side, a "trinity" decision model was constructed to investigate the main factors influencing the scale of coal mining. By introducing the optimal control theory with profit taken as objective function, the coal price and coal reserves were regarded as boundary conditions, and WRCC was set as constraint condition. Based on H-J-B equation algorithm, the decision-making equation for mining scale under the constraints of market demand and WRCC was obtained. Through comparing the mining scales under the two constraints, the mode of "water-based mining scale" was formulated, which is conductive for realizing the balance between coal mining and ecological environment development.

Dielectric tetrahedrons as terahertz resonators switched from perfect absorber to reflector.

Tetrahedrons are basic building blocks in natural and artificial materials, while the terahertz response of micro tetrahedrons has been little explored. Here we fabricate subwavelength ceramic tetrahedrons for use in the terahertz frequency range, and find that the three-dimensional geometry significantly affects their terahertz properties. The transmission spectra are independent of the orientation of the tetrahedrons, while the first magnetic resonance disappears in the reflection spectra when an upright tetrahedron is flipped upside down on the metallic substrate, which changes it from a perfect absorber to a perfect reflector. This is attributed to the destructive interference between two magnetic dipoles induced respectively by the incident and the reflected wave. The study brings new insights in the materials design with 3D building blocks to realize more interesting and exotic terahertz properties.

Synthesis of Thiocarbamoyl Fluorides and Isothiocyanates Using Amines with CF3SO2Cl.

A practical and efficient method to synthesize thiocarbamyl fluorides and isothiocyanates from amines with trifluoromethanesulfonyl chloride was developed. In the presence of the reducing agent triphenylphosphine and sodium iodide, thiocarbamyl fluorides and isothiocyanates were synthesized from secondary/primary amine in moderate to excellent yields, respectively. A broad scope of substrates and good functional group compatibility were observed.

Regioselective Chlorothiolation of Alkenes with Sulfonyl Chlorides.

Newly developed sulfonyl chloride-based regioselective chlorothiolation of alkenes has been disclosed; the reaction is compatible with a variety of functional groups and can be scaled up to the gram scale with no loss in yield. The employment of readily available reactants, mild reaction conditions, and high regioselectivity makes this process very practical. Mechanistic studies revealed a possible free radical reaction pathway.

One-pot synthesis of trifluoromethyl amines and perfluoroalkyl amines with CF3SO2Na and RfSO2Na.

A newly developed CF3SO2Na-based trifluoromethylation of secondary amines has been disclosed, and the method has been successfully extended to the configuration of perfluoroalkyl amines using RfSO2Na, complementing the established synthesis strategy of trifluoromethyl amines. Advantages of the method include good functional group tolerance, mild conditions, and inexpensive or easy-to-handle materials. Mechanistic probes indicate that the thiocarbonyl fluoride formed in situ is the key intermediate in the reaction.

Copper-Catalyzed Vicinal Chloro-thiolation of Alkynes with Sulfonyl Chlorides.

A copper-catalyzed vicinal chloro-thiolation of alkynes with inexpensive and diversified sulfonyl chlorides RSO2Cl (R = aryl, alkyl) has been developed. This practical and scalable reaction could be used for the construction of a number of unexplored bioactive chlorothiolated alkenes. Internal alkynes could also undergo the chloro-thiolation to provide tetrasubstituted alkynes. Preliminary mechanistic investigations revealed a plausible radical process involving a sulfur-centered radical intermediate via copper-mediated homolysis of the S-Cl bond.

Cleaning of Fluid-Infused Surfaces in Microchannels.

When an immiscible fluid is flowing over a fluid-infused surface with transverse grooves in a microchannel, the infused fluid is either left in or cleaned away from the grooves by the flowing fluid. The cleaning status depends on the geometric parameters of the groove and the contact angle of the flowing fluids. The critical width of the grooves for the infused fluid enclosed in or driven out of the grooves is derived. This study helps to understand the stability of the Cassie status in a low-shear flow where the surface tension plays the key role.

Hydrodynamically Formed Uniform Thick Coatings on Microspheres.

Forming uniform thick coatings on microspheres remains a significant challenge in various surface modification and drug delivery applications. In this work, a hydrodynamic method is demonstrated for centering microspheres in droplets with sizes ranging from tens to hundreds of micrometers. The core microspheres stay at the center of the droplets due to the hydrodynamic pressure generated in the surrounding liquid shells, despite the significant density difference between the core microsphere and the liquid shell. Therefore, by using polymerizable liquids that can be solidified thermally or by illumination as the shell layer, core-shell particles with gas, liquid, or solid cores can be surrounded with uniform coatings using the present method.

Size-Dependent Phase Separation in Emulsion Droplets.

Phase separation occurs in emulsion droplets containing poly (ethylene glycol) diacrylate (PEGDA), glycerol, and ethanol to form a glycerol-in-PEGDA structure, and the phase separation process is found to depend on the droplet size. The mechanism of this size-dependent phase separation is dependent on the droplet sizes changing the phase separation time by changing the evaporation speed of mutual solvent ethanol, and the relationship between the separation time T and the droplet diameter D is derived as T≈D2 , which has been validated by experiment results. According to this finding, the structures of the droplets can be designed by applying UV curing at different stages of the phase separation, and the monodispersity of droplets is necessary to achieve polymerized particles with the same structure.

Direct exfoliation of graphite in water with addition of ammonia solution.

To bring graphene closer to its real-world applications, finding a green, low-cost, environment-friendly and less toxic solvent for production of high-quality graphene is highly demanded. However, water, the most widely used green solvent, is generally considered to be a poor solvent for hydrophobic graphene. In this study, we exfoliate graphene nanosheets directly in basic water without surfactants, polymers or organic solvents. The addition of a small amount of ammonia solution achieves the exfoliation of few-layer graphene nanosheets from pristine graphite. Diverse characterization methods are employed to investigate the morphology and quality of as-prepared graphene sheets. The release of gaseous ammonia plays the key role in exfoliation of graphene. The concentration of stable graphene dispersions can reach 0.058mg/mL.

Stable Aqueous Dispersion of Exfoliated Graphene for Tribological Applications.

In this study, the directly exfoliated graphene prepared by a jet cavitation method was tested as additive in pure water toward tribological applications. Reductions of friction coefficient and wear volume up to 22.8% and 44.4% respectively were achieved by addition of the graphene flakes. The as-prepared aqueous graphene dispersions exhibited high stability against sedimentation, and concurrently maintained their tribological properties after deposited for 15 days. The improvement in lubricating and anti-wear performances can be attributed to the graphene network formed on the sliding surfaces during the test.

Mass-Transfer-Induced Multistep Phase Separation in Emulsion Droplets: Toward Self-Assembly Multilayered Emulsions and Onionlike Microspheres.

Mass-transfer-induced multistep phase separation was found in emulsion droplets. The agent system consists of a monomer (ethoxylated trimethylolpropane triacrylate, ETPTA), an oligomer (polyethylene glycol diacrylate, PEGDA 700), and water. The PEGDA in the separated layers offered partial miscibility of all the components throughout the multistep phase-separation procedure, which was terminated by the depletion of PEGDA in the outermost layer. The number of separated portions was determined by the initial PEGDA content, and the initial droplet size influenced the mass-transfer process and consequently determined the sizes of the separated layers. The resultant multilayered emulsions were demonstrated to offer an orderly temperature-responsive release of the inner cores. Moreover, the emulsion droplets can be readily solidified into onionlike microspheres by ultraviolet light curing, providing a new strategy in designing particle structures.

Effects of Processing Parameters on Massive Production of Graphene by Jet Cavitation.

The massive production of graphene by jet cavitation method with high productivity is demonstrated. Effects of the critical processing parameters on the product dispersions are studied systematically. Experimental results show that high yield of graphene flakes relies on appropriate initial concentration of graphite, high jet pressure, and long treating time. By processing a large batch (10 L) of graphite dispersion for 8 h under 20 MPa in the jet cavitation device, an exfoliation fraction of up to ~12 wt% was achieved. Based on statistical analysis of atomic force microscopy, the as-produced graphene flakes were proved to be highly exfoliated, while the distributions of flake thickness and area became narrower with the increase of treating time. Raman spectra confirm that few defects on the graphene basal planes were induced. In general, the presented approach shows advantages in comparison with peer liquid phase exfoliation methods and thus provides a new route in efficiently producing high-quality graphene in large scale.

Investigating the nature of graphene-based films prepared by vacuum filtration of graphene dispersions.

Though the graphene-based films prepared by vacuum filtration of graphene dispersions can be well and easily prepared so far and show great prospects in conductive, transparent, and flexible devices and coatings, the nature of these films has been rarely investigated. In order to reveal how graphene flakes constitute these films, herein we prepared a thin graphene-based film by vacuum filtering graphene dispersions and characterized the film by diverse techniques. Microscopic analyses evidenced the layer structure nature of the film. Raman spectra, transmission electron microscopy, and X-ray diffraction results indicate that the film is neither graphene nor graphite, but intrinsically a graphene block constituted by numerous graphene flakes which are randomly stacked. Though aggregation of graphene flakes happens in the filtration process, the aggregation is not a process to drive graphene flakes stacked in Bernal AB style to form bulk graphite. The adjoining graphene flakes are poorly coupled, likely due to the interlayer adventitious impurities introduced from liquid-phase processing.