Surfactant behavior of "ellipsoidal" dicarbollide anions: a molecular dynamics study

We report a molecular dynamics study of cobalt bis(dicarbollide) anions [(B(9)C(2)H(8)X(3))(2)Co](-) (XCD(-)) commonly used in liquid-liquid extraction (X = H, Me, Cl, or Br), showing that these anions, although lacking the amphiphilic topology, behave as anionic surfactants. In pure water, they display "hydrophobic attractions", leading to the formation of aggregates of different sizes and shapes depending on the counterions. When simulated at a water/"oil" interface, the different anions (HCD(-), MeCD(-), CCD(-), and BrCD(-)) are found to be surface active. As a result, the simulated M(n+) counterions (M(n+) = Na(+), K(+), Cs(+), H(3)O(+), UO(2)(2+), Eu(3+)) concentrate on the aqueous side of the interface, forming a "double layer" whose characteristics are modulated by the hydrophobic character of the anion and by M(n+). The highly hydrophilic Eu(3+) or UO(2)(2+) cations that are generally "repelled" by aqueous interfaces are attracted by dicarbollides near the interface, which is crucial as far as the mechanism of assisted cation extraction to the oil phase is concerned. These cations interact with interfacial XCD(-) in their fully hydrated Eu(H(2)O)(9)(3+) and UO(2)(H(2)O)(5)(2+) forms, whereas the less hydrophilic monocharged cations display intimate contacts via their X substituents. The results obtained with the TIP3P and OPLS models for the solvents are confirmed with other water models (TIP5P or a polarizable 4P-Pol water) and with more polar "oil" models. The importance of interfacial phenomena is further demonstrated by simulations with a high oil-water ratio, leading to the formation of a micelle covered with CCD's. We suggest that the interfacial activity of dicarbollides and related hydrophobic anions is an important feature of synergism in liquid-liquid extraction of hard cations (e.g., for nuclear waste partitioning).     

Acrylic,Elastomeric, Particle‐Dispersed Epoxy‐Clay Hybrid Nanocomposites: Mechanical Properties

Summary: Nanocomposites were formulated by curing a sonicated mixture of epoxy resin, C18 clay, and acrylic rubber dispersants. At 5.5 phr (parts per hundred) organoclay loading and a rubber concentration of 15 phr, the tensile‐failure strain of the nanocomposite was found to be higher than that of epoxy nanocomposite, rubber‐dispersed epoxy, and pristine epoxy. A plausible mechanism for improvement of the failure strain of nanocomposites is proposed.

Stress strain curves of filled and unfilled epoxy specimen.     

Graphene–Epoxy Flexible Transparent Capacitor Obtained By Graphene–Polymer Transfer and UV‐Induced Bonding

A new approach is reported for the preparation of a graphene–epoxy flexible transparent capacitor obtained by graphene–polymer transfer and UV‐induced bonding. SU8 resin is employed for realizing a well‐adherent, transparent, and flexible supporting layer. The achieved transparent graphene/SU8 membrane presents two distinct surfaces: one homogeneous conductive surface containing a graphene layer and one dielectric surface typical of the epoxy polymer. Two graphene/SU8 layers are bonded together by using an epoxy photocurable formulation based on epoxy resin. The obtained material showed a stable and clear capacitive behavior.

     

Structure of decaazonium Tricyclo[28.2.2.213.16]tetratriacontane Decatetrafluoroborate Decahydrate

A new inclusion complex, decaazonium tricyclo[28.2.2.2^13.16]tetratriacontane (L) decatetrafluoroborate decahydrate [(H₁₀L)(BF₄)₁₀10H₂O] (I), has been prepared and characterized by X-ray crystallography. Crystal data: a = 8.156(2), b = 29.125(6), c = 12.981(3) , = 96.76(3)°, space group P2₁/c, Z = 2, the final R = 0.0662 for 5376 reflections with I> 2 (I) (MoK radiation). The azamacrocycle of the complex is a 10-charged cation. The components of the supramolecular system in crystal are stabilized by the hydrogen bonds between the macrocycle cations, the water molecules, and the tetrafluoroborate anions. The water molecules make a solvation shell of the macrocycle forming an octahydrate. The tetrafluoroborate anions alternate with the water molecules stitched to the macrocycle, forming polymer chains in the directions parallel to the z axis of the crystal, and serve as bridges between the macrocycle cations related by the c plane. The set of hydrogen bonds including weak ones unite the components of the complex into a three-dimensional framework. All tetrafluoroborate anions in the structure are disordered.     

Preparation of highly exfoliated epoxy/clay nanocomposites by "slurry compounding": process and mechanisms

Epoxy/clay nanocomposites with a high degree of exfoliation were achieved using a so-called "slurry-compounding" process with which the dispersed state of clay in water can be successfully transferred to an epoxy matrix. In this process sodium montmorillonite was first exfoliated and suspended in water. This suspension was further treated with acetone to form a clay-acetone slurry followed by chemical modification using silane. The modified slurry was then mixed extensively with epoxy to form epoxy/nanoclay composites. It has been shown that the morphologies of clay before and after curing are quite similar and the exfoliation process is termed "slurry compounding". Furthermore, the amount of organic modifier used is only 5 wt % of clay, in contrast to conventional organoclays which normally contain at least 25-45 wt % of organic surfactant. The resulting epoxy/nanoclay composites exhibit a high degree of clay exfoliation and a better thermal mechanical property.     

Trace of the interesting "V"-shaped dynamic mechanism of interactions between water and ionic liquids

The mixture of ionic liquid (1-butyl-3-methylimidazolium tetrafluoroborate, bmimBF4) and water (2.5%, molar fraction) under isothermal conditions at 80 degrees C was investigated by FTIR spectroscopy and two-dimensional correlation infrared spectroscopy (2D-IR) methods. Three regions were focused: the OH stretching band of water (3755-3300 cm (-1)), the stretching band of CH on the imidazole ring (3300-3020 cm (-1)), and the BF stretching band of anions (1310-1260 cm (-1)). During this process, water was gradually evaporated as time passed, which produced influences on the interactions among cations, anions, and water molecules. In the FTIR analysis, we found an interesting "V"-shaped changing trend in peak areas of the C-H on the imidazole ring and the B-F stretching band; the inflection of the system was 913 s, gained through the "moving window" method. A two-step variation was accordingly found during this process. Hydrogen bonds formed by water molecules with cations or water molecules with anions were destroyed by the reduction of water, making a fall in the former period of "V" process, while electrostatic interactions newly formed between anions and cations leading to a rise during the latter period of this course. In this paper, various conformations formed among cations, anions, and water molecules were clearly assigned, and we managed to trace the whole dynamic mechanism of this isothermal process by 2D-IR techniques.     

Hydrodynamic Effect on Secondary Phase Separation in an Epoxy Resin Modified with Polyethersulfone

Summary: The evolution of the morphologies in blends of epoxy/4,4′‐methylenebis(2,6‐dimethylaniline)/polyethersulfone was followed by time‐resolved light scattering, optical microscopy and scanning electron microscopy. The results suggest that, once the diffusion of epoxy molecules cannot follow the geometrical growth, a secondary phase separation occurs, even in the droplet morphology, in which the size of the epoxy‐rich domain grows as usual. The viscoelastic effect of polyethersulfone is also discussed.

Development of morphologies followed by OM: bicontinuous phase separation in the PES‐15.9 blend cured at 140 °C after 80 s.     

Structural distortions and dynamic behavior of the elusive "L"-shaped cis-bicyclo[3.3.0]octenyllithium: X-ray crystallographic and NMR studies

Substituted cis-bicyclo[3.3.0]octenyllithium prepared by addition of t-BuLi to 3-methylene-1,4-cyclooctadiene in the presence of TMEDA crystallizes as a dimer with one unsolvated Li(+) sandwiched between the external faces of two allyl anions in a triple ion, and external to it the second Li(+) is bidentately complexed to TMEDA, 8. Within each allyl unit, the allyl bonds have different lengths, and all four rings deviate from coplanarity which relieves strain in the rings despite introducing partial localization of the allyl anions. A similar structure prevails in solution as shown by (7)Li NMR and the results of (7)Li{(1)H} HOESY and (1)H, (1)H NOESY experiments. Carbon-13 NMR line shape changes indicate that the system undergoes a fast allyl bond shift concerted with conformation shifts of the out of plane carbons, ca. DeltaG = 9 kcal x mol(-1). Cyclopentyllithium prepared by CH(3)Li cleavage of the trimethylstannyl derivative slowly undergoes an allowed ring opening to pentadienyllithium as well as deprotonating the solvent. The different behavior of dienylic lithium species is attributed to the relative separation of their termini.     

Asymmetric allylation of aldehydes and alkylation using "carbon-centered" chiral organosilicon compounds

The effects of the chiral substituents attached to silicon on the stereoselectivity of the reactions of C-centered chiral silicon compounds was examined. The investigation was focused on the asymmetric C-C bond formation reaction of chiral allylsilanes and α-silylallyl anions with aldehydes. The functionalities of the substituents on silicon can be manipulated to improve the stereoselectivities of the reactions remote from silicon atom.     

Electron impact studies. CI—negative ion mass spectra of the carbonyl group. The Aryl?CH2?CO- and Aryl?(CH2)2?CO- systems

Fragmentations of the molecular anions of m- and p-nitrophenyl-CH₂? CO? R yield nitrobenzyl anions in the ion source when R = Ph, but the corresponding ion from the system where R = Me is only formed after collision activation. o- and p-Nitrophenyl parent anions undergo β-cleavage to the carbonyl centre to produce nitrobenzyl anions. Pronounced rearrangement peaks are noted in the spectra of o-nitrophenyl- compounds. Labelling studies indicate the identity of the eliminated species, but the mechanisms of the rearrangements are complex.     

HPLC analysis of carbohydrates on POLYSPHER®CH OH columns using pulsed amperometric detection (PAD) with sodium hydroxide as post column detection reagent

Carbohydrates have been separated on POLYSPHER®CH OH columns using pulsed amperometric detection (PAD) and UV detection ( =196nm) in series and pure water as mobile phase. Nearly baseline separations have been obtained for the glycoprotein carbohydrates of sialic acid (N-acetylneuraminic acid, NANA), N-acetylglucosamine (GlcNAc) and N-acetylgalactosamine (GalNAc). As carbohydrates dissolved and eluted with pure water are present in the neutral form they are not detectable with PAD in contrast to carbohydrate anions formed at high pH values. Therefore an additional NaOH post column reagent has been continuously pumped through a mixing chamber into the mobile phase to form carbohydrate anions resulting in improved detection limits. Monosaccharides as well as glycoprotein carbohydrates could be detected in the g/ml-range. This method has been applied successfully to the analysis of sugars in fruit juice. With only 2 l of juice per 50 ml water, the determination of the main constituents, sucrose, glucose and fructose, was possible in a few minutes without sample preparation.     

Kinetic Study and New Applications of UV Radiation Curing

Highly crosslinked polymers can be readily synthesized by photoinitiated polymerization of multifunctional monomers or functionalized polymers. The reaction can be followed in situ by real‐time infrared (RT‐IR) spectroscopy, a technique that records conversion versus time curves in photosensitive resins undergoing ultrafast polymerization upon UV exposure. For acrylate‐based resins, UV‐curing proceeds with long kinetic chains (7700 mol/radical) in spite of the high initiation rate. RT‐IR spectroscopy proved very valuable in assessing the influence of various parameters, such as initiation efficiency, chemical structure of the telechelic oligomer, light intensity, inhibitory effect of oxygen, on polymerization kinetics. Interpenetrating polymer networks can be rapidly synthesized by means of UV irradiation of a mixture of difunctional acrylate and epoxy monomers in the presence of both radical and cationic‐type photoinitiators. The same UV technology can be applied to crosslink solid polymers at ambient temperature, which bear different types of reactive groups (acrylate and vinyl double bonds, epoxy ring). UV radiation curing has been successfully used to produce within seconds weathering resistant protective coatings, high‐resolution relief images, glass laminates and nanocomposites materials.

Photoinitiated crosslinking polymerization.     

Novel indole based colorimetric and "turn on" fluorescent sensors for biologically important fluoride anion sensing

A novel indole Hydrazone receptor 1 has been synthesized by one step of condensation, which can act as an efficient colorimetric and "turn on" fluorescent sensor for fluoride anions; Benesi-Hildebrand equation indicates that 1 associates with F(-) in a 1:1 stoichiometry; [TBA]OH and (1)H NMR titration experiments indicate that the deprotonation process involved upon addition of fluoride anions.     

Micropatterning of organic semiconductor microcrystalline materials and OFET fabrication by "hot lift off"

Considerable progress toward the development of electronic devices that rely on organic semiconductors as the active material component has been made in recent years. The key step for realization of the advanced organic electronic, or optical, device is the ability to micropattern different kinds of electronic materials, such as organic semiconductor/conducting materials, over large areas with micrometer-sized resolution. Here we demonstrate a simple and direct method for micropatterning small-molecule microcrystalline films using an epoxy stamp. The "hot lift off" method is highly selective, creating patterns with high resolution and relies on straightforwardly tailoring the adhesive properties between the epoxy and the film. This process is well suited for patterning many types of materials.     

Differential Photoluminescent and Electrochemiluminescent Detection of Anions with a Modified Ruthenium(II)–Bipyridyl Complex

Different lights, different selectivies : Luminescence of a new guanidinium 3,3′‐functionalized bipyridyl–Ru^II complex has been studied for sensing of several anions. L ‐Glutamate and dihydrogenphosphate are both detected by photoluminescence and electrochemiluminescence. However, the complex displays differential selectivities for these anions depending on the sensing channels (see scheme).

     

Switching the Solubility of PMMA Bearing Attached Cyclodextrin‐Moieties by Supramolecular Interactions with Ionic Liquids

Methacrylate‐modified β‐cyclodextrin (β‐CD) and methyl methacrylate (MMA) have been radically copolymerized to obtain hydrophobic CD copolymers. The water‐insoluble copolymers are able to form highly stable inclusion complexes with anions of ionic liquids. Surprisingly, the inclusion of the anions in the CD cavity results in a significant change of thermal and solution properties. Furthermore, it can be shown that the structure of the ionic liquid anions influences the coil structure of the copolymers. The obtained results could be proven by means of microcalorimetry, differential scanning calorimetry, and dynamic light scattering.

     

"Naked-eye" screening of metal-based chemosensors for biologically important anions

A two-step "naked-eye" screening of selective metal-based chemosensors for biologically important anions such as cyanide, phosphate, and oxalate from commercially available metal indicators and metal ions has been developed. Applications in food safety control have been demonstrated.     

Unraveling the molecular recognition of "three methylene spacer" bis(benzimidazolium) moiety by dibenzo-24-crown-8: pseudorotaxanes under study

"Three methylene spacer" bis(benzimidazolium) derivatives act as a new template for threading dibenzo-24-crown-8 into [2]pseudorotaxanes. In this Article we sought to unveil the difference in the extent of threading of various "three methylene spacer" bis-benzimidazolium moieties based on differences in aromatic methyl substituent positions and anions through the macrocycle dibenzo-24-crown-8. The temperature of the systems were also varied (low temperatures of 240 K and 253 K), when such interwinding of the thread and crown were not detected at room temperature of 308 K. The presence of such threaded complexes was determined based on (1)H-NMR initially and finally corroborated by high resolution mass spectrometry and DFT calculations. 2D-NMR experiments ((1)H-(1)H-NOESY) proved to be a very important tool in elucidating the interaction present between the components of the pseudorotaxanes. The dethreading/rethreading process was studied. DFT optimized structures suggest lower energy H-bonding orientations and compare the effect of methyl substituents on the axle.     

羟甲基环氧树脂的“邻位效应”的探讨

邻位羟甲基环氧树脂由于在其缩水甘油醚基的邻位引入了羟甲基而使环氧基反应活性提高。本文合成了邻位和对位羟甲基苯基缩水甘油醚作为模型化合物,通过差热分析和红外光谱研究了它们与4,4′-二氨基二苯甲烷的反应,并对Schwarzer提出的“邻位效应”进行了探讨。     

Comparison of Covalently and Noncovalently Functionalized Carbon Nanotubes in Epoxy

Carbon nanotubes typically require the use of a dispersing or stabilizing agent to prevent significant aggregation during incorporation into a polymer matrix. These additives must be strongly associated, either covalently or physically, to achieve their purpose. In this study, multi‐walled carbon nanotubes (MWNTs) were dispersed into an epoxy matrix using polyethylenimine (PEI) as a dispersant that was either covalently attached to the nanotubes or physically mixed to result in only noncovalent interaction. Epoxy composites containing covalently modified MWNTs exhibited greater storage modulus and reduced electrical conductivity.