Electronegative Fluorine Research Articles

Tuning the properties of graphene quantum dots by passivation.

The electronic and optical properties of graphene quantum dots (GQDs) of size less than 10 nm are different from those of graphene sheets due to quantum confinement effects. For analyzing their use in optoelectronic applications, it is very crucial to optimally tune the bandgap and engineer the controlling parameters. In the present work, a systematic investigation of the band gap of hexagonal GQDs has been carried out by examining their HOMO and LUMO energies. Passivation of dangling bonds of these GQDs has been carried out with the help of electron-withdrawing substituents in order to tune the band gap and engineer their optical properties such as absorption and emission spectra by carrying out the simulation with Density Functional Theory formalism using Gaussian 09 software. Carrying out passivation with electronegative element fluorine (F) effectively decreases the band gap of these QDs resulting in a redshift in the absorption spectra. The HOMO and LUMO topographical surfaces have been used to understand the absorption spectra. These surfaces show some σ-bond characteristics along with π-bond properties on passivating GQDs with the F-atom which further results in alteration of their energies and a corresponding decrease in their band gap. Here, the absorption is found to be dependent on the size of GQDs and the type of passivating atoms (H or F). The results thus obtained are found to be in good consonance with those reported in the literature engaging different methods. The present analysis may prove to be useful in improving the working of solar cells and other optoelectronic devices.

Visible light degradation of tetracycline by hierarchical nanoflower structured fluorine-doped Bi2WO6

Fluorine-doped Bi2WO6 samples were synthesized by a simple one-step hydrothermal method. The structure and the photocatalytic performance of the as-prepared catalysts were systematically investigated using a variety of characterization methods. Meanwhile, the possible mechanism of photodegradation was discussed. Combined with the analysis of X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and energy dispersive spectrometry (EDS), it was proved that fluorine has been successfully doped into the Bi2WO6 (BWO) crystal lattice, and its crystal structure remains orthorhombic. With the doping of fluorine, the morphology of Bi2WO6 changed from a two-dimensional ultrathin nanosheet to a hierarchical nanoflower microstructure. This hierarchical nanoflower structure as well as the strong electronegativity of fluorine are the reasons for the enhanced degradation of pollutants (tetracycline, TC for short). For the optimum composition labeled as F-BWO4, the apparent rate constant (k) of degrading TC is about 4.5 times that of Bi2WO6, and the degradation rate decreased by only 10% over four cycle degradation experiments.

Improve the Photo-Activity of TiO2 from a Dual Modification via Tungsten-Doping and Fluorination

Transition metal doping is a proven feasible and practical modification technique to extend the absorption range of TiO2 from ultraviolet to visible light while retard the recombination of photogenerated electron and hole and facilitate rapid interfacial charge transfer. Surface modification also greatly influence the adsorption and reaction rate. Fluorination has become one of the most effective methods for surface acidification due to the strong electronegativity of fluorine. The ≡Ti-F group transfers electrons to the O atoms on the surface of fluorinated TiO2 to capture photoelectrons. The general modification approaches utilizing insoluble tungstic acid or highly toxic hydrofluoric acid to improve charge separation and transfer in TiO2 result in considerable issues such as uneven doping, significant impact on morphology and size, as well as serious environmental hazards. In this work, we have developed an environmental benign simple one-pot dual-modification approach that using sodium tungstate of high solubility and trace-level sodium fluoride as replacements. The combined characteristic analyses and density functional calculation (DFT) suggest that the remarkable improvement of the photo-activity of TiO2 can be attributed to the rapid charge separation and transfer due to the bandgap narrowing from tungsten doping and localized spatial charge separation from fluorination.

First-principle investigations of negative differential resistance in zigzag boron nitride nanoribbons

This work investigates the structural stability, electronic and transport properties of zigzag boron nitride nanoribbons (ZBNNRs) with hydrogenation/fluorination by using density functional theory (DFT) along with non-equilibrium Green’s function (NEGF) approach. The study reveals that ZBNNRs exhibit metallic to semiconducting transition via selected edge fluorination. Interestingly, edge fluorinated ZBNNRs demonstrate high structural stability due to the higher electronegativity of fluorine. It is also revealed that negative differential resistance (NDR) has also been observed for edge fluorinated two terminal devices with enormously high peak to valley current ratio (PVCR) of the order of 1 0 11 . We have also investigated the gate controllable current–voltage (I–V) characteristics of three terminal ZBNNRs field effect transistor (FET). The selective structures exhibit excellent gate controllability which can tune the observed PVCR. Our findings indicate the potential of fluorinated ZBNNRs towards upcoming ultra fast switches, rectifiers and oscillators etc. • This work investigates the structural stability, electronic and transport properties of zigzag boron nitride nanoribbons (ZBNNRs) with hydrogenation/ fluorination by using density functional theory (DFT) along with non-equilibrium Greens function (NEGF) approach. • It is revealed that negative differential resistance (NDR) has also been observed for edge fluorinated two terminal devices with enormously high peak to valley current ratio (PVCR) of the order of 10 11 . We have also investigated the gate controllable current–voltage (I–V) characteristics of three terminal ZBNNRs field effect transistor (FET). • The selective structures exhibit excellent gate controllability which can tune the observed PVCR. • Our findings indicate the potential of fluorinated ZBNNRs towards upcoming ultra fast switches, rectifiers and oscillators etc.

Structural proof of a [C\u2013F\u2013C]+ fluoronium cation

Organic fluoronium ions can be described as positively charged molecules in which the most electronegative and least polarizable element fluorine engages in two partially covalent bonding interactions to two carbon centers. While recent solvolysis experiments and NMR spectroscopic studies on a metastable [C–F–C]+ fluoronium ion strongly support the divalent fluoronium structure over the alternative rapidly equilibrating classical carbocation, the model system has, to date, eluded crystallographic analysis to confirm this phenomenon in the solid state. Herein, we report the single crystal structure of a symmetrical [C–F–C]+ fluoronium cation. Besides its synthesis and crystallographic characterization as the [Sb2F11]− salt, vibrational spectra are discussed and a detailed analysis concerning the nature of the bonding situation in this fluoronium ion and its heavier halonium homologues is performed, which provides detailed insights on this molecular structure.

Improving stability and reversibility via fluorine doping in aqueous zinc–manganese batteries

Constructing stable and reversible manganese-based cathode is one of the key technologies of aqueous Zn/MnO2 batteries (AZMBs). Herein, a rational strategy of fluorine doping is proposed to improve the reversibility and activity of MnO2. According to the strong bonding induced by high electronegativity of fluorine, the integrity of frameworks can stabilize, and the ion diffusion kinetics is promoted. Meanwhile, the strong ‘pinning effect’ of fluorine effectively retains the electrochemical activity and guides the reversible electrochemical behavior, which plays a critical role in improving both the cycle life and energy efficiency. As expected, a significant specific capacity of 300 mAh/g at 0.6 C and impressive stability over 1,200 cycles at 5 C are achieved without obvious decay. Such high stable Zn/F–MnO2 system may provide novel perspectives for designing high-performance AZMBs.

Probing the effect of chiral dopant fluorination on dielectric and electro-optical properties of the ferroelectric liquid crystalline mixture

In this article, fluorinated chiral dopant-assisted tuning of dielectric and electro-optical properties of a ferroelectric liquid crystal (FLC) material is presented. Five new FLC mixtures with room temperature ferroelectric phase were formulated by fluorinating the phenyl core of chiral dopant at different positions and with a different number of fluorine atoms. The dielectric and electro-optical properties of all the FLC mixtures were systematically studied. It is found that the permittivity value of ferroelectric mesogens can be tuned between 5 and 36 (at 100 Hz) with fluorination. Also, the dielectric loss factor decreases owing to fluorination of chiral dopant with a shift in phason mode relaxation towards the low-frequency side. In addition, there is a significant change in material parameters of FLC, such as phase transition temperature, response time, spontaneous polarization, and rotational viscosity due to fluorination in chiral dopant. The presence of highly electronegative fluorine acts as a source of potentially repulsive force. It partially screens the molecular chirality of the dopant, which resulted in a change in the material parameters of FLCs. Interestingly, there is no considerable change in the mesogenic structure and orientation with the addition of fluorine, which is confirmed through wide-angle X-ray scattering. These studies open up a new avenue for tailoring the dielectric and electro-optical properties of mesogens for advanced device applications based on FLCs.

Effect of fluorination on the adsorption properties of aromatic heterocycles toward methyl halides: A quantum chemical study

Despite the numerous publications describing the synthesis and electronic properties of fluorinated furan, thiophene and pyrrole, the systematic overview of their adsorption applications is still lacking. In this study, the effect of fluorination on the adsorption properties of furan (C4H4O), thiophene (C4H4S), pyrrole (C4H4NH) and benzene (C6H6) are investigated with the help of density functional theory (DFT) calculations. Herein, the adsorption energies of CH3X (X = F, Cl & Br) on C4H4O, C4H4S, C4H4NH and C6H6 and their fluorinated analogues are calculated using ωB97XD/6-31+G(d, p) level of theory. The results of the adsorption energies and symmetry adapted perturbation theory (SAPT0) reveal that the adsorption affinity of adsorbent is enhanced upon fluorination due to the increasing dispersion forces. To comprehensively investigate the variation in the electronic properties of nonfluorinated and fluorinated systems, the HOMO, LUMO orbitals and NBO charges are analyzed. The isosurfaces of orbitals show that the electron density is more localized onto the fluorinated adsorbents which are probably due to the presence of multiple electronegative fluorine atoms. Owing to the electron-withdrawing nature of fluorine, the electronic charges are transferred from CH3X to fluorinated adsorbents while the charges are shifted from nonfluorinated adsorbents to CH3X. Furthermore, the TD-DFT calculations reveal that the electronic transition energies are significantly decreased in most of the fluorinated complexes especially, CH3X@C4F4S and CH3X@C4F4NH. With these findings, it can be postulated that fluorine substitution can significantly surge the electronic and adsorption properties of sensor materials.

Design and Synthesis of Fluoro Analogues of Vitamin D.

The discovery of a large variety of functions of vitamin D3 and its metabolites has led to the design and synthesis of a vast amount of vitamin D3 analogues in order to increase the potency and reduce toxicity. The introduction of highly electronegative fluorine atom(s) into vitamin D3 skeletons alters their physical and chemical properties. To date, many fluorinated vitamin D3 analogues have been designed and synthesized. This review summarizes the molecular structures of fluoro-containing vitamin D3 analogues and their synthetic methodologies.

Emergent Fluorous Molecules and Their Uses in Molecular Imaging.

This Account summarizes recent advances in the chemistry of fluorocarbon nanoemulsion (FC NE) functionalization. We describe new families of fluorous molecules, such as chelators, fluorophores, and peptides, that are soluble in FC oils. These materials have helped transform the field of in vivo molecular imaging by enabling sensitive and cell-specific imaging using magnetic resonance imaging (MRI), positron emission tomography (PET), and fluorescence detection. FC emulsions, historically considered for artificial blood substitutes, are routinely used for ultrasound imaging in clinic and have a proven safety profile and a well-characterized biodistribution and pharmacokinetics. The inertness of fluorocarbons contributes to their low toxicity but makes functionalization difficult. The high electronegativity of fluorine imparts very low cohesive energy density and Lewis basicity to heavily fluorinated compounds, making dissolution of metal ions and organic molecules challenging. Functionalization is further complicated by colloidal instability toward heat and pH, as well as limited availability of biocompatible surfactants.We have devised new fluorous chelators that overcome solubility barriers and are able to bind a range of metal ions with high thermodynamic stability and biocompatibility. NE harboring chelators in the fluorous phase are a powerful platform for the development of multimodal imaging agents. These compositions rapidly capture metal ions added to the aqueous phase, thereby functionalizing NEs in useful ways. For example, Fe3+ encapsulation imparts a strong paramagnetic relaxation effect on 19F T1 that dramatically accelerates 19F MRI data acquisition times and hence sensitivity in cell tracking applications. Alternatively, 89Zr encapsulation creates a sensitive and versatile PET probe for inflammatory macrophage detection. Adding lanthanides, such as Eu3+, renders NE luminescent. Beyond chelators, this Account further covers our progress in formulating NEs with fluorophores, such as cyanine or BODIPY dyes, with their utility demonstrated in fluorescence imaging, biosensing, flow cytometry and histology. Fluorous dyes soluble in FC oils are also key enablers for nascent whole-body imaging technologies such as cryo-fluorescence tomography (CFT). Additionally, fluorous cell-penetrating peptides inserted on the NE surface increase the uptake of NE by ∼8-fold in weakly phagocytic stem cells and lymphocytes used in immunotherapy, resulting in significant leaps in detection sensitivity in vivo.

Enhanced DC Surface Insulation of Al2O3/ER Brought by the Permeability of Fluorine-Containing Release Agent

The objective of this paper is to propose an equivalent fluorination method to improve the DC surface insulation strength of Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> /ER composites using fluorine-containing release agent (F-RA). By replacing the conventional silicon series release agent with a fluorine-containing one, the DC flashover voltage is, at best, raised to 1.2 times of the original value, and the surface charge characteristics are modified for better suppressing the distortion of surface electric field. The trap depth of the material is shallow, and the surface conductivity is reduced. The modification mechanism is explained from the perspectives of surface conductivity and fluorine electronegativity.

Local Solvation Modulates Activity of Covalent C−F Bonds in Fluorinated Electrolyte Additives

Fluorinated reactants that enable fluoride bond cleavage, either in electrolytes or cathodes, are receiving increased research attention because of the formation of highly stable decomposition products (e.g. LiF), which also allows large Gibbs free energy change. Electrolytes using fluorinated solvents or additives (e.g. fluoroethylene carbonate (FEC), methyl 2,2,2-trifluoroethyl carbonate (FEMC), and liquefied CH3F) were shown to be able to effectively increase Li cyclability by forming LiF rich solid electrolyte interphase (SEI) on Li. In addition, conversion type Li battery cathodes, such as transition-metal fluorides (MFy, M=Fe, Co, Ni, Cu, y=2, 3) and CFx, can deliver high energy densities through fluoride bond reduction reactions. However, the strong electronegativity of fluorine making most of the fluoride bonds highly stable (i.e. hard to break), which limits their applications in electrochemical systems. Therefore, fundamental understanding of how to modulate fluoride bond strength to unlock activity is of vital importance. Herein, we use perfluoroalkyl group (RF)-containing liquid reactants as model systems to demonstrate that the covalent C−F bonds in RF, which were generally believed to be extremely difficult to reduce, can be unlocked through combined reactant-electrolyte design, with the electrolyte playing a central role in governing activity. The interaction between solvent and fluorinated reactants, such as solvation effects and formation of hydrogen bonds, can alter the electron density distribution along the carbon-fluorine skeleton and weaken fluoride bond strengths as indicated by nuclear magnetic resonance (NMR) spectroscopy and density functional theory (DFT) calculations. As a result, the reduction potential (from galvanostatic measurements for Li cells) can be dramatically increased from < 2.0 V to > 2.9 V vs. Li/Li+ through modulation of the solvent. In addition to activating electrochemically-active pathways, solvent molecules also need to exhibit proper polarities to allow both high miscibility (requiring low polarity), and Li salt solubility (requiring high polarity). Other electrolyte design aspects that can direct the reduction activity of highly fluorinated reactants will also be discussed, including fluoridation of solvent molecules, Li salt dissociation energy, and reactant/salt ratio. These understandings on tuning fluoride bond strength via electrolyte−reactant interactions will open up new design opportunities for fluorinated electrolyte components, either solvents or additives, for Li cells with high cycle stabilities, as well as high-energy Li primary battery with liquid cathodes.

Adsorption of Rare Earth Ce3+ and Pr3+ Ions by Hydrophobic Ionic Liquid.

This study reports the use of hydrophobic ionic liquid (IL) based on D-galactose for the recovery of Ce (III) and Pr (III) ions from solutions. The equilibrium data were obtained by optimization of batch parameters, and various isotherms and kinetic models were utilised to predict the mechanistic process of sequestration of ions. The Arrhenius activation energies are found to be between 5–40 kJ, suggesting the physisorption process of ions onto IL. The present process is understood to be rapid and exothermic in nature according to thermodynamic experiments. The loading capacity was found to be 179.3 g L−1 and 141.5 g L−1, respectively, for Ce (III) and Pr (III) ions at pH 5 with a contact time of 30 min and dose being 0.1 g L−1. The higher uptake capacity is attributed to the presence of a highly electronegative fluorine atom in the IL. These results highlight the potential application of IL in the sequestration of Ce (III) and Pr (III) ions from any water sources.

Fluorinated pillared-layer metal-organic framework microrods for improved electrochemical cycling stability

Developing metal-organic framework (MOF)-based materials with good cyclic stability is the key to their practical application. Fluorinated organic compounds are usually highly chemically stability due to the high electronegativity of fluorine. Also, the pillared-layer structures based on coordination bonds have better structure and thermal stability than those based on hydrogen bonds. Herein, the fluorinated pillared-layer [Ni(2,3,4,5-tetrafluorobenzoic acid)(4,4′-bipyridine)]n MOF ([Ni(TFBA)(Bpy)]n) materials were constructed through a facile room-temperature solution reaction and used as electrode materials for supercapacitors. Surprisingly, the size/morphology of Ni(TFBA)(Bpy)]n MOFs could be adjusted by varying the synthesis time. Benefting from the short ion diffusion length, unique pillar-layer structure, and strong intercomponent synergy of organic ligands, the Ni(TFBA)(Bpy)]n MOF microrods showed a higher electrochemical energy storage capability than bulk MOFs. At the same time, compared to the non-fluorinated [Ni(benzoic acid)(Bpy)]n MOFs (31.5% capacitance decay), the fluorinated Ni(TFBA)(Bpy)]n MOFs have a higher cycle stability with only 2.6% capacitance loss after 5000 cycles at 3 mA/cm2.

Well-Defined Fluorinated Copolymers: Current Status and Future Perspectives

Well-defined fluoropolymers exhibit unique properties such as excellent oil and water repellency, satisfactory thermal stability, a low refractive index, and low surface energy. The origin of these properties is attributed to the presence of a strong electronegative and low polarizable fluorine atom in the backbone of such polymers, which leads to a strong C–F bond (with a high bond dissociation energy of 485 kJ mol–1). Because of these features, these polymers have found applications as functional coatings, thermoplastics, biomedical items, separators, and binders for Li ion batteries, fuel cell membranes, piezoelectric devices, high-quality wires and cables, and so forth. Usually, fluoropolymers are synthesized by the conventional radical (co)polymerization of fluoroalkenes, which leads to the production of (co)polymers with an ill-defined end group, uncontrolled molar mass, and high dispersity values. In the last two decades, significant developments of various reversible deactivation radical polymerization (RDRP) techniques have helped the design of macromolecular architectures (including block, graft, star, and dendrimers) on demand. However, for relevant new applications, well-defined fluoropolymers with controlled macromolecular architectures (e.g., block copolymers as thermoplastic elastomers and electroactive polymers or graft copolymers for fuel cell membranes) are required. Several RDRP methods, developed in the last two decades, have paved the way for the synthesis of (co)polymers with well-defined molar mass, dispersity, chain end-functionality, and macromolecular architectures. Some of these RDRP techniques have been successfully employed for the synthesis of well-defined fluorinated copolymers. These techniques include iodine-transfer polymerization (ITP), reversible addition–fragmentation chain-transfer (RAFT) polymerization, organometallic-mediated radical polymerization (OMRP), and, to a lesser extent, nitroxide-mediated polymerization (NMP). Impressive control of the molar mass parameters of the fluoropolymers synthesized via these techniques also encouraged the researchers to combine these techniques with other postpolymerization strategies, leading to innovative novel polymeric materials. Thus, synthesized well-defined fluoropolymers exhibited a unique combination of properties (such as excellent weather resistance, high thermal/chemical/aging resistance, morphological versatility, and a low dielectric constant/flammability/refractive index). These led to the application of such developed materials in various high-technology applications such as high-performance elastomers, coatings for marine antifouling applications, fluorinated surfactants, fuel cell membranes, and gel polymer electrolytes for Li ion batteries. Newer advances in the field of polymer synthesis techniques are the need of the hour in order to synthesize more advanced fluorinated materials which may change the use of such polymers in engineering and biomedical fields in the current century. However, it should be kept in mind that success in this regard shall heavily depend on a deeper understanding of the polymerization process and structure–activity relationships.

Synthesizing novel NH4CoxNi1-xF3 as electroactive material for supercapacitors using 2-methylimidazole: Study of reaction durations

Zeolite imidazolate framework-67 (ZIF67) with high surface area is one of promising metal–organic frameworks as electroactive material for supercapacitors (SC). Energy storage ability of electroactive material is primarily influenced by morphology, which is confined via structure-directing agent (SDA). It is the first time to use NH4F as SDA to develop novel bimetallic ZIF67 derivative, NH4CoxNi1-xF3 (NCNF), as electroactive material for SC. The polyhedron structure of ZIF67 is greatly evolved to particle-aggregated sphere (PAS) when NH4F is incorporated. Different reaction times are used for synthesizing NCNF to understand PAS formation mechanism. The NCNF electrode prepared using 24 h shows the highest specific capacitance (CF) of 490.4 F/g at 20 mV/s, due to less grain boundaries between smooth particles for assembling huge sphere, while bimetallic ZIF67 synthesized without NH4F merely shows CF value of 2.7 F/g. The largely enhanced CF value for NCNF electrode with NH4F incorporation is benefitted from novel PAS formation and high electronegativity of fluorine. The SC composed of optimized NCNF electrodes shows CF value of 150 F/g at 1 A/g, maximum energy density of 19.7 Wh/kg at 500 W/kg, and excellent cycling stability with CF retention of 100% and Coulombic efficiency of 76% after 5000 times charge/discharge process.

Properties of triacetatecellulose composite materials with additives tris[three (butoxy)(polyfluoroalkoxy)titaniumoxy] boranes

Studies have been performed on the modification of triacetatecellulose soluble compositions tris[three(butoxy)(polyfluoroalkoxy)titaniumoxy]boranes by the laboratories in which the length of the polyfluoroalkoxyl radical changed. At the initial stage, experiments were conducted to study the effect on the viscous characteristics of the initial solutions of TAC compositions of different temperature ranges, the values of the velocities of the concussion as for the initial base composition and with the introduction into the composition of the solution of different number of initial components, on the basis of which the target additives are synthesized, namely, polyfluoropic alcohol or tris[three(butoxy)titanoxy]borane. When introduced into the basic soluble composition of small amounts of polyfluorine alcohol FFА-3 (up to 0,1 % of the mass. from the mass of TAC) and a shear rate of 0,99c-1 there is a sharp increase in viscosity to 1,56 P·s, that is connected, apparently, with the implementation of a new type of hydrogen bonds between electronegative fluorine atoms and positively charged carbon atoms in the structure of solvents and TAC links (in complexes, simple ethers, glycosidic bonds and methylene groups at free hydroxylates). The implementation of such connections is accompanied by an increase in the volume of assocites, which are formed, ie indicates an increase in the viscosity of the solution of the sample TAC - composition. This interaction, with the formation of associations, takes place, first of all, on the surface of small supramolecular formations of TAC, obtained in the previous initial crushing of large supramolecular groups in solution. In this case, in the basic solution of the TAC-composition, there is a process of reversal of the TAC, namely, consolidation of the sizes of supramolecular formations. It is shown that the studied series of bor-, titanium-, (butoxy(polyfluoroalkoxy)-containing products, are effective modifiers of triacetate-cellulose soluble composite materials, allowing at the outflow stage, such as film materials or artificial silk threads, to adjust in a wide range, in the direction of increase, viscosity of the solution and at the same time increase the strength of finished products to break. The achievement of the obtained positive effect is due to the implementation in the polymer matrix of a new type of physical interactions between the electronegative fluorine atoms in the additive and the electropositive carbon atoms of the TAC molecule, as well as the coordination bonds between B and Ti additives and oxygen links TAC polymer. At the same time, internal stresses in the polymer matrix are reduced or virtually disappeared. Thus, studies have shown that polyfluoropic alcohols, tris- [three (butoxy)titanoxy]borane and products of its transesterification by polyfluoropic alcohols of different molecular weight are effective modifiers of soluble TAC compositions (as regulators of viscosity of solutions at the stage of outflow of films), and additives that increase the relative strength of their films by 2–3 times the strength of the films to break; their relative hardness), it is most advisable to use such a number of compounds in quantities of up to 1,0 % of the mass. from the mass of TAC. The obtained results can be used to significantly improve the quality of products from triacetatecellulose or in the recycling of products and waste on its basis.

The Shock Induced Mechanical Response of the Fluorinated Tri-polymer, Viton B

The response of Viton B, a fluorinated tripolymer, to one dimensional shock loading has been investigated using manganin stress gauges as the diagnostic. These have been mounted such that they are sensitive to both the longitudinal and lateral components of stress. In the case of the longitudinal gauges, mounting at multiple locations within the target assembly also allows measurement of shock and release velocities as well. Results show that in terms of shock velocity and stress and shear strength, results from Viton B lie a little higher than the corresponding results for polytetrafluoroethylene (PTFE), but more similar to those of polyvinylidene difluoride (PVDF). However, in terms of the release velocity, the behaviour of Viton B is more akin to PTFE. We believe that there are two competing mechanisms at play; an electrostatic repulsion between chains due to the presence of electronegative fluorine atoms that acts against interchain interactions (hence the low shock and high release velocities) and interchain entanglement (tacticity) due to the presence of trifluoromethyl side groups on one of the monomer sub units. This will result in a greater shock velocity and increase in shear strength behind the shock front (when compared to PTFE) as adjacent polymer chains physically interact via entanglement. This should reduce the release velocity for similar reasons; however the release behaviour of Viton B and PTFE is similar. We thus suggest that the electrostatic repulsion between chains may be acting over a longer length scale than interchain entanglement.

Role of fluorine on the structure and second-harmonic-generation property of inorganic selenites and tellurites

Inclusion of the most electronegative fluorine can regulate the distortion direction and magnitude of the structure, bandgap, and second-harmonic-generation (SHG) efficiency of materials effectively.

Formation of atomic fluorine anions in 12CaO·7Al2O3

The storage of atomic fluorine anions (F−) is an important issue in the development of emission materials that have numerous technological applications including catalysis. Using density functional theory simulations, we examine the formation of F− ions from gaseous F2 in the nanoporous complex oxide 12CaO·7Al2O3 (C12A7). Both stoichiometric and electride forms of C12A7 strongly encapsulate fluorine atoms, and the formation of F− ions is confirmed from the charge analysis. There is a significant enhancement in the encapsulation in the electride form of C12A7 due to the presence of electrons in its nanocages. Successive encapsulation of multiple F atoms is also energetically favorable in both forms of C12A7. The formation of molecular fluorine (F2) in the nanocages of both forms is unfavorable due to the strong electronegativity of fluorine.