Degree Of Fluorination Research Articles

Fluoro-graphene: nonlinear optical properties

In the present work, we report on the investigation of the third-order nonlinear optical response of graphene fluoride dispersed in DMF and also of fluorosurfactant-stabilized graphene fluoride dispersed in water under visible (532 nm) and infrared (1064 nm), picosecond and nanosecond laser excitation. Both graphene derivatives were found to exhibit large nonlinear optical response, while significant differences on their nonlinear optical response have been observed (e.g. different sign of nonlinear refraction and absorption). These findings highlight the important role of the degree of fluorination of the graphene sheets on their optical and electronic properties. Furthermore, DMF dispersed graphene fluoride was found to exhibit important broadband optical limiting action under nanosecond laser excitation, making it promising candidate for optical limiting applications.

Influence of fluorination on the characterization of fluorotelomer-based acrylate polymers by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry

The relative degree of fluorotelomer-based acrylate polymers (FTACPs) fluorination was demonstrated to influence the sample preparation protocol for matrix-assisted laser desorption/ionization time-of-flight (MALDI-ToF) mass spectrometry. A homologous series of FTACPs were synthesized from fluorotelomer and hydrocarbon acrylates of different chain lengths, which varied the ratio of perfluorinated to hydrogenated carbons (RF/RH). The solubility of FTACPs in tetrahydrofuran (THF) and chloroform was observed to decrease for highly fluorinated FTACPs (RF/RH>0.5) promoting FTACP aggregation. No dependence on the degree of fluorination was observed for the solubility of FTACPs in the fluorinated solvents α,α,α-trifluorotoluene (TFT) or dichloropentafluoropropanes (HCFC-225). For FTACPs with a low degree of fluorination such as poly(8:2 FTAC-co-HDA) (RF/RH=0.375), MALDI-ToF analysis was successful using a conventional sample preparation protocol with THF, and dithranol (Dith) matrix. Conversely, the poor solubility of the highly fluorinated poly(8:2 FTAC-co-BA) (RF/RH=1.5) in THF resulted in mass discrimination. Several fluorinated sample preparation protocols were evaluated for poly(8:2 FTAC-co-BA) using TFT and HCFC-225, and decafluoroazobenzene (DFAB) or 2-[(2E)-3-(4-tert-butylphenyl)-2-methylprop-2-enylidene]malononitrile (DCTB) matrices. The high volatility of HCFC-225 decreased FTACP pooling during solvent evaporation in comparison to the less volatile TFT, and improved the quantity of detectable signals. MALDI-ToF analysis of poly(8:2 FTAC-co-BA) in a 95:5 HCFC-225:methanol with DCTB being the best sample preparation protocol for highly fluorinated FTACPs in this study producing the highest number of observable signals. Employing a fluorinated sample preparation offers the capability of analyzing other highly fluorinated polymers that are not compatible with conventional sample preparations.

Omniphobic “RF Paper” Produced by Silanization of Paper with Fluoroalkyltrichlorosilanes

The fabrication and properties of “fluoroalkylated paper” (“RF paper”) by vapor‐phase silanization of paper with fluoroalkyl trichlorosilanes is reported. RF paper is both hydrophobic and oleophobic: it repels water (θappH2O>140°), organic liquids with surface tensions as low as 28 mN m‐1, aqueous solutions containing ionic and non‐ionic surfactants, and complex liquids such as blood (which contains salts, surfactants, and biological material such as cells, proteins, and lipids). The propensity of the paper to resist wetting by liquids with a wide range of surface tensions correlates with the length and degree of fluorination of the organosilane (with a few exceptions in the case of methyl trichlorosilane‐treated paper), and with the roughness of the paper. RF paper maintains the high permeability to gases and mechanical flexibility of the untreated paper, and can be folded into functional shapes (e.g., microtiter plates and liquid‐filled gas sensors). When impregnated with a perfluorinated oil, RF paper forms a “slippery” surface (paper slippery liquid‐infused porous surface, or “paper SLIPS“) capable of repelling liquids with surface tensions as low as 15 mN m‐1. The foldability of the paper SLIPS allows the fabrication of channels and flow switches to guide the transport of liquid droplets.

Fluorine Patterning in Room-Temperature Fluorinated Graphite Determined by Solid-State NMR and DFT

Fluorination of graphite at room temperature allows producing graphite fluoride compounds with a controlled content of fluorine. Here we combine solid-state NMR spectroscopy and DFT calculations to study the structure and reveal the fluorine patterning in graphite fluorides C2Fx intercalated with acetonitrile. Two major chemical states of carbon, namely the atoms covalently bound to fluorine and the bare atoms, are detected by 13C MAS NMR irrespective of the degree of fluorination. The data indicate that although all graphene sheets were subjected to fluorination, the near-planar configuration is preserved. The interaction between host C2Fx matrix and acetonitrile molecules is of van der Waals character. Decomposition of the 19F MAS NMR spectra reveals occurrence of at least six fluorine environments in each sample. By DFT calculations distinct 19F chemical shifts are attributed to isolated, end chain, “linked” (which include midchain, cyclic, and branched) CF groups and infinite CF arrays. The assignment is confirmed by 19F RFDR, which is sensitive to dipolar coupling. Analyzing the data for C2Fx samples with different degrees of fluorination x, an evolution of the fluorine pattern is proposed. The reported calculated 19F NMR shielding parameters provide classification criteria for assignment of 19F NMR chemical shifts in fluorinated carbon materials.

On the polarity of partially fluorinated methyl groups

A series of indole and 5-methoxyindole derivatives, substituted at C3 with n-propyl or 4-methylcyclohexyl scaffolds bearing varying degrees of fluorination of the terminal methyl group, have been prepared and studied. These compounds exhibit characteristic polarity patterns, measured either by logP or chromatographic capacity factors, which are consistent with the partially known lipophilicity pattern for the corresponding n-propylbenzene series. Based on a simple CF bond vector analysis, the polarity increase upon exchange of a terminal methyl by a trifluoromethyl group in an aliphatic substituent should be comparable to that arising from a single H/F exchange at the terminal methyl group, while the volume increase in the former case is three times larger than that in the latter. This may explain the observation that replacement of a methyl by a fluoromethyl group results in a more pronounced lowering of molecular lipophilicity than its replacement by a trifluoromethyl group. The same analysis predicts a difluoromethyl group to exhibit a lipophilicity reduction similar to that of a fluoromethyl group.

High-performance n-channel thin-film transistors with acene-based semiconductors

Two acene-based semiconductors were investigated with respect to their performance as n-type materials in organic field-effect transistors. The partially fluorinated ditetracenes (Ditetracen is protected by copywrite through the Patent WO/2007/000268. The patent is property of the Dritte Patentportfolio Beteiligungsgesellschaft mbH & Co. KG.) (DT) were synthesized in a high yield with different degrees of fluorination, one with four and another with two fluorine substituents (named as DT-4F and DT-2F, respectively). Both materials exhibit high thermal stability, with decomposition temperatures above 500°C. Since both materials are supposed to have a lowered LUMO level compared to the non-fluorinated parent DT, n-type operation in thin-film transistors (TFTs) with gold source and drain contacts was expected. TFTs based on DT-2F, however, showed weak ambipolar transport only, which demonstrates insufficient fluorination to switch from hole-dominated to electron-dominated transport. On the other hand, high performance n-type TFTs have been achieved from DT-4F, with electron mobilities up to 1.0cm2/Vs. This result indicates that fluorinated DT material can act as excellent n-type semiconductor for applications in complementary circuits. This is demonstrated in a complementary inverter stage using DT-4F-based TFTs as n-type transistor and a non-fluorinated DT derivative-based TFT as p-type transistor.

Influence of the degree of fluorination on the behaviour of silica particles at air–oil surfaces

We study the behaviour of fumed silica particles coated to different extents with a perfluoro-alkoxysilane in mixtures of air and liquid, for liquids ranging from non-polar hydrocarbons and polar oils to glycerol and water. Comparisons are made with equivalent hydrophilic and very hydrophobic (hydrocarbon-coated) particles. The surface energy of the particles, calculated from contact angle data, decreases upon increasing the degree of fluorination. As a result, an oil dispersion of particles forms in liquids of low surface tension, e.g. silicone oil, with particles of low fluorine content (oleophilic). Particle-stabilised air-in-oil foams form both in systems of oils of higher tension (>32 mN m−1, e.g. sunflower oil) and particles of intermediate fluorine content and with oils of lower tension (down to 27 mN m−1, e.g. hexadecane) and particles of high fluorine content. The foamability of the oils increases with particle concentration and the majority of foams are stable to coalescence and disproportionation for at least 6 months. In many of the oil–particle combinations stabilising foams, oil-in-air liquid marbles can also be prepared, with particles of highest fluorine content encapsulating oils of lowest surface tension. Contact angles of the liquid in air on rough surfaces spin coated with the particles vary from ca. 80° to 150° for systems forming oil foams and oil liquid marbles. Omniphobic surfaces can be prepared relatively easily using such particles.

The impact of fluorination on the structure and properties of self-assembled monolayer films

The adsorption of partially fluorinated amphiphiles on metal/metal oxide surfaces allows for the generation of specifically fluorinated thin-film interfaces. Such surfaces are often compared to polytetrafluoroethylene (PTFE), which exhibits a low surface energy, accompanied by biological and chemical inertness, making perfluorinated interfaces applicable to a wide range of technologies. In thin-film research, self-assembled monolayers derived from fluorinated alkanethiols (FSAMs) serve as well-defined systems that can be used to evaluate the physical and chemical properties of interfaces produced with varying degrees of fluorination. The characteristics of these surfaces have been attributed to both the chemical composition of the individual molecular adsorbates and the consequent structural features associated with monolayers formed from these unique partially fluorinated adsorbates. Specifically, this review seeks to correlate the structural and interfacial properties of FSAMs on gold with the structure/composition of the fluorinated moiety present in the adsorbed molecules and to highlight how the degree of fluorination influences the interfacial ordering of the individual alkanethiolate chains and the vacuum energy levels of the modified metal substrate. Additionally, the thermal stability of these organic thin films is analyzed as a function of adsorbate structure. Included are highlights of some of the studies in which FSAMs, formed from a variety of new types of surfactants, were used to modify colloidal systems, to generate anti-adhesive materials, and to enhance the stability of fluorinated thin films toward low-energy electron degradation.

Poly(arylene ether) Ionomers with Pendant Quinuclidium Groups and Varying Molecular Weight for Alkaline Electrodes

The properties of the ionomer used to construct electrodes for direct methanol anionic fuel cells are critically important to the fuel cell performance. In this study, a new polymer backbone with a higher degree of fluorination for increased hydrophobicity has been shown to improve both the alkaline anode and cathode performance. It was also shown that decreasing the molecular weight of the ionomer improves fuel cell performance. Finally, higher fuel cell performance was observed with quinuclidinium head groups on the anionic ionomer, in comparison to the more traditional trimethyl ammonium cation. The improvements in performance appear to be due to improved mass transport of reactants and products through the electrode as a result of increased free volume within the electrode and a more efficient construction of the electrical double layer at the ionomer/catalyst interface.

Tuning the morphology of triblock terpoly(2-oxazoline)s containing a 2-phenyl-2-oxazoline block with varying fluorine content

The formation of nanostructures in triblock terpolymers consisting of poly[2-ethyl-2-oxazoline-block-2-(1-ethylpentyl)-2-oxazoline-block-2-(Xfluorophenyl)-2-oxazoline] (X = di, tri, tetra and penta) was investigated in water. For this purpose a gradually increasing degree of fluorination was introduced in the molecular structures and its influence on the self-assembly was studied. It can be demonstrated that the basic form of aggregation of these systems resembles rod-like micelles, which tend, upon introduction of fluorinated blocks, to aggregate first into 2-dimensional and later into 3-dimensional super-aggregates. In the case of di- and pentafluorinated terpolymers well-defined structures were observed, which represent likely intermediate, stable transient structures formed during an assumed rod-to-vesicle transition. DLS and cryo-TEM were utilized to analyze the structural features of these nanostructures and a model for their further assembly into super-structures was developed.

Superhydrophobic Films Fabricated by Electrospraying Poly(methyl methacrylate)-b-poly(dodecafluoroheptyl methacrylate) Diblock Copolymers

We present the fabrication of superhydrophobic surfaces by electrospraying structure controlled poly(methyl methacrylate-bromine) (PMMA-Br) homopolymer and degree of fluorination controlled poly(methyl methacrylate)-b-poly(dodecafluoroheptyl methacrylate) (PMMA-b-PDFMA) copolymers synthesized via atom transfer radical polymerization (ATRP). The flow rate has great effects on the surface hydrophobicity of PMMA50.6, and superhydrophobic surface was obtained at a higher flow rate of 5 μL/min. For fluorinated diblock copolymers, superhydrophobic surfaces can be obtained by electrospraying PMMA50.6-b-PDFMA0.8 and PMMA147.9-b-PDFMA17.5 at the selected flow rates. X-ray photoelectron spectroscopy (XPS) detections reveal that, during the film formation, more hydrophobic surfaces would be fabricated due to the surface segregations of C–C and C–H groups with THF as solvent instead of C–O–C═O group with DMF as solvent. This investigation may be of great value in fabricating superhydrophobic polymer materials.

Synthesis and IR spectroscopic characterization of fluorinated graphite intercalation compounds with chlorinated derivatives of methane and ethane

We have synthesized (C2FxBr0.01 · yG)n intercalation compounds with (C2FxBr0.01)n as a host and G (dichloromethane, chloroform, carbon tetrachloride, and dichloroethane) as a guest (x and y are stoichiometric coefficients). The behavior of the functional groups in the guest and host subsystems has been studied by IR spectroscopy. We have examined the influence of the degree of fluorination of the polymer host (0.5 < x < 1.0) and the nature of the guest on the vibrational frequencies of the C-F and C-Cl bonds.

π–π Interaction Assisted Hydrodefluorination of Perfluoroarenes by Gold Hydride: A Case of Synergistic Effect on C–F Bond Activation

"Synergistic effect" is prevalent in natural metalloenzymes in activating small molecules, and the success has inspired the development of artificial catalysts capable of unprecedented organic transformations. In this work, we found that the attractive π-π interaction between organic additives (as electron-donors) and the perfluorinated arenes (as electron acceptors) is effective in gold hydride catalyzed activation of C-F bonds, specifically hydrodefluorination (HDF) of perfluoroarenes catalyzed by the Sadighi's gold hydrides [(NHC)AuH] (NHC = N-heterocyclic carbene). Although a weak interaction between [(NHC)AuH] and perfluoroarenes was observed from (1)H NMR and UV-vis spectroscopies, low reactivity of [(NHC)AuH] toward HDF was found. In contrast, in the presence of p-N,N-dimethylaminopyridine (DMAP), the HDF of perfluoroarenes with silanes can be efficiently catalyzed by [(NHC)AuH], resulting in mainly the para-hydrodefluorinated products with up to 90% yield and 9 turnovers. The yield of the reaction increases with the more electron-withdrawing groups and degree of fluorination on the arenes, and the HDF reaction also tolerates different function groups (such as formyl, alkynyl, ketone, ester, and carboxylate groups), without reduction or hydrogenation of these function groups. To reveal the role of DMAP in the reactions, the possible π-π interaction between DMAP and perfluoroarenes was suggested by UV-vis spectral titrations, (1)H NMR spectroscopic studies, and DFT calculations. Moreover, (1)H and (19)F-NMR studies show that this π-π interaction promotes hydrogen transfer from [(NHC)AuH] to pyridyl N atom, resulting in C-F bond cleavage. The interpretation of π-π interaction assisted C-F activation is supported by the reduced activation barriers in the presence of DMAP (31.6 kcal/mol) than that in the absence of DMAP (40.8 kcal/mol) for this reaction. An analysis of the charge distribution and transition state geometries indicate that this HDF process is controlled by the π-π interaction between DMAP and perfluoroarenes, accompanied with the changes of partial atomic charges.

Significantly reduced fluorination time needed for suppression of space charge in polyethylene by increasing the fluorination temperature

Polyethylene samples were surface fluorinated using a F2/N2 mixture under 0.1 MPa at 35, 70 or 95 °C for different times. Space charge accumulation was found to show four basic types for each fluorination temperature with increasing fluorination time. But the fluorination times needed for the formation of the same type of charge accumulation are significantly different between the different temperature treatments. For example, the 60 min fluorination at 95 °C is sufficient to form the fourth type of charge accumulation (almost no space charge in the bulk), while this is not achieved even for the 360 min fluorination at 35 °C. Infrared analyses and scanning electron microscopy cross-section images of the fluorinated samples indicate the increases in the degree of fluorination and thickness of the fluorinated layer with fluorination time. These different types of charge accumulation arise from different blocking abilities between the fluorinated layers to both charge injection and extraction. The fluorinated layers formed at different temperatures with good blocking ability have almost the same high degree of fluorination and large thickness of about 0.70 µm. This indicates that the increase in fluorination temperature has no negative influence on the electrical properties of the formed surface layer.

Electronic and Magnetic Properties of Fluorinated Graphene with Different Coverage of Fluorine

We have studied the electronic and magnetic properties of fluorinated graphene with different coverage of fluorine using first-principles calculations based on the density functional theory. The atomic structures, adsorption energies, and electronic structures of fluorinated graphene are investigated. Our results show that the electronic and magnetic properties of fluorinated graphene sheet exhibit strong dependence on the degree of fluorination. A precise adsorption of fluorine enables a tuning of the band gap from 0 to ∼3.13 eV as well as a transformation from nonmagnetic semimetal to nonmagnetic/magnetic metal, or to magnetic/nonmagnetic semiconductor. Therefore, our study suggests that the property of graphene can be modified by absorbing different amounts of fluorine.

Synthesis of fluorinated graphene with tunable degree of fluorination

An easy, low-cost and effective synthesis of fluorinated graphene with tunable C/F atomic ratio (RC/F) has been realized by the reaction between dispersed graphene oxide and hydrofluoric acid. The results show that fluorine is grafted onto the basal plane of graphene, and the RC/F can be easily adjusted by controlling the reaction conditions. The as-synthesized fluorinated graphene exhibits a sheet-like morphology with 1–2 layered thickness and tunable bandgap energy from 1.82 to 2.99eV, which has potential applications in optoelectronic and photonic devices.

Interconversion of ephedrine and pseudoephedrine during chemical derivatization

Gas chromatography-mass spectrometry (GC-MS) analysis after heptafluorobutyric anhydride (HFBA) derivatization was one of the published methods used for the quantification of ephedrine (EP) and pseudoephedrine (PE) in urine. This method allows the clear separation of the derivatized diastereoisomers on a methyl-silicone-based column. Recently the authors came across a human urine sample with apparently high levels (µg/ml) of EP and PE upon initial screening. However, duplicate analyses of this sample using the HFBA-GC-MS method revealed an unusual discrepancy in the estimated levels of EP and PE, with the area response ratios of EP/PE at around 29% on one occasion and around 57% on another. The same sample was re-analyzed for EP and PE using other techniques, including GC-MS after trimethylsilylation and ultra-high-performance liquid chromatography-tandem mass spectrometry. Surprisingly, the concentration of EP in the sample was determined to be at least two orders of magnitude less than what was observed with the HFBA-GC-MS method. A thorough investigation was then conducted, and the results showed that both substances could interconvert during HFBA derivatization. Similar diastereoisomeric conversion was also observed using other fluorinated acylating agents (e.g. pentafluoropropionic anhydride and trifluoroacetic anhydride). The extent of interconversion was correlated with the degree of fluorination of the acylating agents, with HFBA giving the highest conversion. This conversion has never been reported before. A mechanism for the interconversion was proposed. These findings indicated that fluorinated acylating agents should not be used for the unequivocal identification or quantification of EP and PE as the results obtained can be erroneous.

Phosphate-Based Compounds as Additives for 5-Volt Lithium-Ion Electrolytes

We have shown in previous work that fluorinated phosphate esters make effective additives to the standard carbonate-based electrolyte used in commercial and experimental Li-ion batteries. New results indicate that the degree of fluorination seems to have an effect on the performance of these additives in helping the full cell retain capacity during cycling tests. Experimental evidence gathered from half cell and full cell data lead us to hypothesize that fluorinated phosphate esters are participating in the formation of a tougher, more redox-resistant solid electrolyte interphase layer on both anode and cathode. Therefore, we propose a network-forming mechanism in which fluorinated phosphate esters function to protect the electrolytes from the electrodes in our tested Li-ion battery systems.

UV photodissociation dynamics of iodobenzene: Effects of fluorination

The UV photochemistry of various fluorinated iodobenzenes (4-fluoro-, 2,4-difluoro-, 3,5-difluoro-, and perfluoro-iodobenzene) has been investigated at many wavelengths by velocity map imaging, time-resolved near infrared absorption spectroscopy and (spin-orbit resolved) ab initio calculations of the ground and excited state potentials along the C-I stretch coordinate, R(C-I). The textbook description of the near UV photochemistry of CH(3)I, i.e., σ∗←n excitation to the (3)Q(0+) state, followed by direct dissociation (to yield spin-orbit excited iodine atom (I∗) products) or by non-adiabatic coupling via a conical intersection (CI) with the (1)Q(1) potential (to yield ground state iodine (I) atoms) is shown to provide a good zero-order model for aryl iodide photochemistry also. However, the aryl halides also possess occupied π and low-lying π∗ orbitals, and have lower (C(2v) or C(s)) symmetry than CH(3)I. Both of these factors introduce additional subtleties. For example, excitations to and predissociation of ππ∗ excited states provide additional routes to I products, most obviously at long UV wavelengths. nσ∗∕πσ∗ configuration mixing stabilizes the (analogue of the) (3)Q(0+) potential energy surface (PES), to an extent that scales with the degree of fluorination; the corresponding 4A(1) PES in C(6)F(5)I is actually predicted to exhibit a minimum at extended R(C-I). This has the effect of extending the long wavelength threshold for forming I∗ products. The lowered symmetry enables an additional (sloped) CI with the 5A(2) (9A(") in 2,4-difluorobenzene) PES, which provides an extra non-adiabatic route to (fast) ground state I atoms when populating the 4A(1) PES at shorter UV excitation wavelengths.

Significantly improved piezoelectric thermal stability of cellular polypropylene films by high pressure fluorination and post-treatments

Cellular polypropylene (PP) films were fluorinated under a high pressure of 13 bar of the F2/N2 mixture and were post-treated by nitrous oxide and isothermal crystallization. The fluorinated and post-treated PP films after being expanded and corona charged exhibit a significantly improved piezoelectric thermal stability. After annealing at 70 °C for 151 h or at 90 °C for 224 h, the piezoelectric d33 value of the fluorinated and post-treated piezoelectric sample still retains 58% or 45% of its initial d33 value, while the corresponding value of the virgin piezoelectric sample has decreased to 29% or 15% of the initial value. Chemical composition analysis of the cross section of the fluorinated and post-treated film by energy-dispersive x-ray spectroscopy indicates that the internal layers have been fluorinated, in spite of a lower degree of fluorination compared with the fluorinated surface layer. Short-circuit and open-circuit TSD current measurements reveal that the fluorinated internal layers, like the fluorinated surface layer, also have very deep charge traps, although there probably is a difference in density of the deep traps between them. The deeply trapped charge on the internal layers of the fluorinated and post-treated piezoelectric sample is responsible for its significantly improved piezoelectric thermal stability.