Low Fluorine Content Research Articles

Superhydrophobic and oleophobic surfaces containing wrinkles and nanoparticles of PEDOT with two short fluorinated chains

Superhydrophobic and oleophobic surfaces are obtained by electrodeposition of original PEDOT derivatives containing two short fluorinated chains. The liquid-repellent properties are due to the combination of high intrinsic hydrophobicity and oleophobicity of polymers due the presence of two fluorinated chains, and the formation of wrinkles and spherical particles induced by the electrodeposition process. The presence of wrinkles and spherical particles and as a consequence the surface hydrophobicity and oleophobicity is correlated to the fluorinated chain length and electrochemical parameters (the deposition charge for the depositions at constant potential and the scan rate and number of scans for the depositions by cyclic voltammetry). Here, the increase in the number of wrinkles and spherical particles induces an increase in the surface roughness increasing especially the surface hydrophobicity while the surface oleophobicity is not always affected. However, it is also possible to increase the surface oleophobicity by a careful choice in the electrochemical parameters. This work also allows the elaboration of super liquid-repellent surfaces with low fluorine content (materials with low bioaccumulative potential).

Defect complexes in fluorine-implanted germanium

In the present article we employ positron annihilation lifetime spectroscopy and secondary ion mass spectrometry to study the thermal evolution of vacancy related defects in fluorine-implanted germanium. We find that fluorine enriches the germanium matrix with various vacancy-like clusters that show both concentration and annealing temperature-dependent behaviour. We demonstrate that low fluorine concentrations saturate the Ge matrix with large concentrations of divacancy-like complexes that are effectively removed after moderate annealing. High fluorine concentrations, however, appear to stabilize a large component of monovacancy-like complexes in the near-surface region of the Ge substrates. These monovacancy-like complexes also appear to be thermodynamically stable, even after high-temperature annealing. The nucleation and thermal evolution of these vacancy-like defects may have particular importance in the fabrication and control of future germanium electronic devices.

A water-free metal organic deposition method for YBa2Cu3O7−δ thin film fabrication

During the fabrication of YBa2Cu3O7−δ (YBCO) thin films via the metal organic deposition (MOD) method, the water content of the precursor solution should be reduced to prevent precipitation and other detriment. In most of the reported MOD-YBCO studies, water was used as a solvent, and vacuum distillation was utilized to reduce the water content of the precursor solution. In this study, we propose a water-free MOD method using propionic anhydride and methanol as the solvents. The crystal water of raw precursor salts was removed by heating, and the water content in the final precursor solution was as low as 0.2 wt%. Using this solution with low fluorine content and the optimized maximum temperature of pyrolysis, the final YBCO thin films about 250 nm thick had the critical current density (Jc) of 3.8 MA cm−2 (77 K, self-field). The water content of the precursor solution was further reduced to less than 10−2 wt% by vacuum distillation. According to the Jc performance, thermal analysis, x-ray diffraction investigations, and morphology observations, no significant improvement was found for the final YBCO thin films fabricated by the distilled solution, indicating that vacuum distillation is not necessary in the water-free MOD method.

Tribological properties of hard a-C:H:F coatings

Hydrogenated amorphous carbon thin films containing fluorine (a-C:H:F) have been produced by radio-frequency plasma enhanced chemical vapor deposition by using different F/H ratios in the gas phase. The introduction of fluorine from 0 to 19at.% resulted in a decrease of hydrogen content and to the formation of CF and CF2 bonds. For all the films, Raman analysis showed a typical diamond-like carbon response with an evolution of the structure to larger sp2 clusters with less hydrogen while fluorine content increased. The drop in hardness generally observed in the literature with fluorine introduction was less abrupt here: for a fluorine content up to 6.5at.%, the measured hardness was 28GPa, and for 19at.% of fluorine, value was 20GPa. These are quite high values for a-C:H:F thin films. Moreover, fluorine improved tribological behavior in dry conditions with friction coefficient slightly reduced at low fluorine content and wear rate significantly reduced: divided by two to four than the fluorine free reference coating.

LiFSI vs. LiPF6 electrolytes in contact with lithiated graphite: Comparing thermal stabilities and identification of specific SEI-reinforcing additives

Lithium bis(fluorosulfonyl) imide (LiFSI) is regarded as an alternative to the classical LiPF6 salt in today's LiFePO4/graphite-based Li-ion batteries electrolyte owing to its slightly higher conductivity and lower fluorine content. In an attempt to better evaluate the safety issues, here we report the comparative study of the LiFSI and LiPF6 based electrolyte/lithiated graphite interface thermal behavior. DSC measurements with LiFSI-based electrolyte reveal a sharp exotherm with large heat release though at higher onset and peak temperatures compared to LiPF6-based electrolyte. With the help of GC/MS, 19F NMR and ESI-HRMS analyses, we assume that this highly energetic peak around 200°C, which is dependant upon the lithium content, is mainly related to electrochemical reduction of FSI− anion. In a strategy to limit the probability and damage of thermal runaway event, electrolyte additives such as vinylene carbonate (VC), fluoro ethylene carbonate (FEC), di-isocyanato hexane (DIH) and toluene di-isocyanate (TDI) have been investigated and shown to significantly lower the energy associated with the exothermic phenomenon.

Evolution of low fluorine solution in decomposition and crystallization for YBa2Cu3Oy film growth

A new chemical solution deposition process for YBCO films based on a low fluorine content solution has been developed. The total content of fluorine in this solution is about 50% of that in all TFA solution, the amount of corrosive fluorine-containing gas released can be greatly reduced and the acute decomposition in a short time can be suppressed. A smooth and homogeneous surface have been achieved at the heating rate of 5K/min by using this low fluorine solution. During the crystallization process, the composition of intermediated phases (BaYF, CuO) are changed with the annealing temperature. The reaction of nanocrystal Y2O3 and CuO is accompanied with the nucleation of YBCO phase, which indicates that there may be less second phase formation in the crystallization process. The traces of intermediate phase (BaYF–Ba(O,F)2) are observed. It demonstrates that the growth mechanism of the low fluorine solution is still “ex situ BaF2” process. The YBCO films with a fast pyrolysis process has been demonstrated high performance with Jc (77K, self field)=∼3.2MA/cm2.

Thermal stability and mechanical properties of fluorinated diamond-like carbon coatings

Diamond-like carbon (DLC) coatings with variable fluorine content were produced by a plasma assisted chemical vapour deposition (PACVD) technique, based on a remote plasma configuration. The feed gas consisted of mixtures of C2H2 and CF4 and the fluorine percentage in the coatings was in the range of 0–36at.%. Competition between fluorine and hydrogen in defining the coating composition is discussed. Microindentation experiments were performed to evaluate hardness and elastic modulus, which were found to decrease as the fluorine content increases. A similar trend was shown by the internal stress of the coatings. Adhesion to the substrate was assessed by scratch tests and high critical load was achieved with moderate fluorine content (12at.%). The counteracting effects of internal stress and interface toughness may explain this behaviour.The thermal stability of the coatings was investigated by performing annealing treatments in a vacuum furnace at 500°C for variable times. All tested samples maintained their integrity at the end of the heat treatments, but the fluorine content and hardness decreased as the annealing time increased. Coatings with low fluorine content retained good hardness after being annealed for 57.6ks (16h).

Fluorine intercalation in the n = 1 and n = 2 layered manganites Sr2MnO3.5+x and Sr3Mn2O6

Fluorine insertion into the oxygen defect superstructure manganite Sr2MnO3.5+x has been shown by transmission electron microscopy (TEM) to result in two levels of fluorination. In the higher fluorine content sections, the fluorine anions displace oxygen anions from their apical positions into the equatorial vacancies, thus destroying the superstructure and reverting to a K2NiF4-type structure (a=3.8210(1)Å and c=12.686(1)Å). Conversely, lower fluorine content sections retain the Sr2MnO3.5+x defect superstructure, crystallising in the P21/c space group. Fluorine intercalation into the reduced double-layer manganite Sr3Mn2O6 occurs in a step-wise fashion according to the general formula Sr3Mn2O6Fy with y=1, 2, and 3. It is proposed that the y=1 phase (a=3.815(1)Å, c=20.29(2)Å) is produced by the filling of all the equatorial oxygen vacancies by fluorine atoms whilst the y=2 phase (a=3.8222(2)Å, c=21.2435(3)Å) has a random distribution of fluorine anions throughout both interstitial rocksalt and equatorial sites. Neutron powder diffraction data suggest that the fully fluorinated y=3 phase (a=3.8157(6)Å, c=23.666(4)Å) corresponds to the complete occupation of all the equatorial oxygen vacancies and the interstitial sites by intercalated fluorine.

Influence of long alkyl spacers in the elaboration of superoleophobic surfaces with short fluorinated chains

In order to produce extremely high oleophobic properties with a low fluorine content, long dodecyl spacers were introduced between a polymer and fluorinated chains in order to reduce the mobility of the fluorinated chains, especially short perfluorobutyl (F-butyl) chains. We report the synthesis and characterization of electrodeposited polymer surfaces obtained from original fluorinated 3,4-ethylenedioxypyrrole (EDOP) derivatives. Semi-fluorinated chains of three different lengths (F-octyl: PEDOPC12F8, F-hexyl: PEDOPC12F6 and F-butyl: PEDOPC12F4) were grafted to EDOP and separated with a n-dodecyl chain in order to reduce the mobility of F-butyl chains. For the first time, a surprisingly high contact angle of 138° was measured with hexadecane on PEDOPC12F4, although F-octyl tails are necessary to produce robust superoleophobic surfaces. By producing smooth surfaces, we successfully separate the influence of the intrinsic hydro- and oleophobicity and the surface structuration on the static contact angles of water and hexadecane. Here, the surface structuration increases the contact angle of hexadecane by 90° for PEDOPC12F4. The Cassie–Baxter equation predicts a porosity of 84.5% between the surface and a hexadecane droplet.

Fluorinated graphene based electrodes for high performance primary lithium batteries

A single step strategy capable of improving specific capacity, power capability and faradic yield of a Li/CFx battery system is developed. The excellent electrochemical performance achieved here using fluorinated graphene with a very low fluorine content (x = 0.22) could lead to the development of highly efficient primary battery systems with low cost and minimum environmental impact.

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.

From ZnF2 to ZnO thin films using pulsed laser deposition: Optical and electrical properties

The growth of Zn-based thin films, from pure ZnF2 to pure ZnO, has been investigated as a function of the oxygen partial pressure and substrate temperature using pulsed laser deposition. Starting from (1−x) ZnO−x·ZnF2 target compositions, ZOF films containing a low fluorine content (x<0.10) have been successfully deposited. These films exhibit typical ZnO wurtzite structure while maintaining the (002) preferred orientation. The fluorine doping does not modify the film transparency (T≈90%), whereas for a high fluorine content, a large haze effect is observed. Such effects are associated with increased surface roughness. The Hall effect measurements show a beneficial effect with the addition of F corresponding to a decrease in resistivity for ZOF thin films accounting for oxygen to fluorine substitution in the ZnO structure. In contrast, attempts at annealing in air of successfully deposited pure ZnF2 thin films does not lead to increased conductivity in the films; this is associated with a progressive transformation from ZnF2 to ZnO. Finally, improvements in the electrical properties are proposed for F and Si co-doping, and resistivities as low as 7.2×10−4Ωcm for SZOF thin films deposited at RT from a ZnO (87at%)–ZnF2 (10at%)–SiO2 (3at%) target are achieved.

Passivation of Porous Silicon by LaF&lt;SUB&gt;3 &lt;/SUB&gt;Using a Simple Single-Source Chemical Bath Technique

Passivation of porous silicon (PS) by LaF<SUB>3</SUB> by a novel chemical-bath technique has been investigated in this report. The porous silicon surface has been passivated with LaF<SUB>3</SUB> by reacting LaCl<SUB>3</SUB> with HF in the etching chamber at room temperature. Without removing the porous silicon from the anodizing chamber LaF<SUB>3</SUB> as a result of chemical reaction between LaCl<SUB>3</SUB> and HF was allowed to passivate the PS surface. Several cycles of reaction that gives the various thickness of LaF<SUB>3</SUB> layer on PS have been investigated. The Scanning Electron Microscopy (SEM) on the surface of LaF<SUB>3</SUB>/PS/Si structure confirms the LaF<SUB>3</SUB> film deposition on PS layer. The X-ray diffraction (XRD) of the deposited layer revealed a hexagonal nanocrystalline LaF<SUB>3</SUB> deposition. The as-deposited thin (10-cycle) LaF<SUB>3</SUB> layer contained very low concentration of lanthanum (La) and fluorine (F). The concentration of La and F started increasing with the increase in reaction cycle. But the photoluminescence (PL) of as deposited-LaF<SUB>3</SUB> passivated PS was lower than that of fresh PS. Annealing the just passivated PS structure recovered the PL intensity. Experimental results show that the optimized chemical bath passivation process for the LaF<SUB>3</SUB> on porous silicon could enable the porous silicon to be an important material for photonic application.

Hybrid CO2-philic Surfactants with Low Fluorine Content

The relationships between molecular architecture, aggregation, and interfacial activity of a new class of CO(2)-philic hybrid surfactants are investigated. The new hybrid surfactant CF2/AOT4 [sodium (4H,4H,5H,5H,5H-pentafluoropentyl-3,5,5-trimethyl-1-hexyl)-2-sulfosuccinate] was synthesized, having one hydrocarbon chain and one separate fluorocarbon chain. This hybrid H-F chain structure strikes a fine balance of properties, on one hand minimizing the fluorine content, while on the other maintaining a sufficient level of CO(2)-philicity. The surfactant has been investigated by a range of techniques including high-pressure phase behavior, UV-visible spectroscopy, small-angle neutron scattering (SANS), and air-water (a/w) surface tension measurements. The results advance the understanding of structure-function relationships for generating CO(2)-philic surfactants and are therefore beneficial for expanding applications of CO(2) to realize its potential using the most economic and efficient surfactants.

Spin dephasing of fluorine-bound electrons in ZnSe

The spin coherence of an ensemble of electrons bound to fluorine donors in epitaxially grown ZnSe layers is studied by time-resolved pump-probe Kerr rotation. Long-lived spin dephasing with decay times up to ${T}_{2}^{*}=33$ ns is found for a sample with a low fluorine concentration of $1\ifmmode\times\else\texttimes\fi{}{10}^{15}$ cm${}^{\ensuremath{-}3}$ at cryogenic temperatures. The time is close to the limit set by nuclear-spin fluctuations, for which we measure a strength of 1.65 mT. We find ${T}_{2}^{*}$ to be constant up to 40 K, with a strong drop for higher temperatures. The dephasing time also shortens with increasing fluorine concentration, indicating an interaction between the spins at different fluorine centers.

Fluoro‐functionalized PLA polymers as potential water‐repellent coating materials for protection of stone

AbstractA series of sixteen fluoro‐functionalized poly(lactic acid)s were synthesised using two commercial fluorinated alcohols [3,3,4,4,5,5,6,6,7,7,8,8,8‐tridecafluoro‐1‐octanol and 4‐(3,3,4,4,5,5,6,6,7,7,8,8,8‐tridecafluorooctyl)benzyl alcohol] as co‐initiators in the ring‐opening polymerization of L‐lactide and rac‐lactide (the racemic mixture of L‐ and D‐lactide) catalyzed by Tin(II) 2‐ethylhexanoate. The polymers were characterized by NMR, IR, GPC, DSC and tested as potential protective coating for stone. The performances were comparatively evaluated in terms of water protection efficacy and colour changes of the treated stone. Furthermore, the photo‐stability of nine selected polymers under Solar Box condition was also investigated. It has been shown that the presence of fluorine makes the stone more water‐repellent. The polymers showed also interesting photo‐stability and some of them provided a behavior close to PLA‐FLK‐PLA block copolymers recently reported in the literature, in spite of their lower fluorine content © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

In vitro inhibitory effect of drinking water from south Algeria on the dissolution of dental hydroxyapatite

Epidemiological surveys in Algeria conducted in the school health program show that the dental carious prevalence is about 67%. Water is the main source of fluorine, recognized as the essential chemical element to prevent carious dental For this purpose, the objective of this study is to test, in vitro, the inhibitory effect of Saharan fluoridated water for the dissolution of hydroxyapatite Ca5(PO4)3OH, under physiological conditions: acid (HNO3) at pH = 5.1 and T = 37 ° C. Thence, the fluoride content of drinking water of some Saharan region was measured, it varies from 0.48 to 3.87 ± 0.05 mg / L.The Inhibitory effect of waters is between 54.28 and 83.1%, VC &lt;5%. In addition, a low concentration of fluorine [F-] = 0.25 mg / L reduced the solubility (S) of hydroxyapatite by a factor of 2. Thus, the studied Sahara waters inhibit ‘in vitro’ the dissolution of hydroxyapatite Ca5 (PO4)3OH.

Fluorinated sulfonate surfactants

New classes of fluorinated sulfonate surfactants were synthesized in which a perfluoroalkyl chain is interrupted either by an ether oxygen (–O–), or by methylene (–CH 2–) units. Both classes of molecules involve multi-step syntheses. The fluoroether sulfonates (RfOCF 2CF 2CH 2CH 2SO 3H, Rf = C 2F 5, C 3F 7) were achieved in four steps including fluoroiodonation of perfluorovinyl ethers (RfCF = CF 2), ethylation, chlorination and hydrolysis. The methylene interrupted fluorosulfonates (RfCH 2CF 2CH 2CH 2SO 3H, Rf = C 4F 9, C 6F 13) were also prepared in four steps involving vinylidene fluoride insertion of fluoroalkyl iodides, ethylene insertion, chlorination and hydrolysis. All intermediates and final products were well characterized by 1H and 19F NMR. These new fluorinated surfactants were compared to a commercially available fluorosulfonate (C 6F 13CH 2CH 2SO 3H) for surface activity. These materials match the surface tensions of commercial fluorosurfactant yet are more efficient because they have lower fluorine content.

The properties of fluorine-containing diamond-like carbon films prepared by pulsed DC plasma-activated chemical vapour deposition

Diamond-like carbon films containing up to 23.1 at. % of fluorine (F-DLC), were deposited onto silicon substrates by low-frequency, pulsed DC, plasma-activated, chemical vapour deposition (PACVD). The influence of fluorine on plasma current density, deposition rate, composition, bonding structure, surface energy, hardness, stress and biocompatibility was investigated and correlated with the fluorine content. X-ray photoelectron spectroscopy (XPS) analysis revealed the presence C–C, C–CF and C–F for F-DLC films with a low fluorine concentration (1.5–12.1 at. %), however for films with a higher fluorine content (23.0 at. %) an additional peak due to CF 2 bonding was detected. The addition of fluorine into the DLC film resulted in lower stress and hardness values. The reduction in these values was attributed to the substitution of strong C=C by weaker C–F bonds which induces a decrease in hardness. Ion scattering spectrometery (ISS) measurements revealed the presence of fluorine atoms in the outmost layer of the F-DLC films and there was no evidence of surface oxygen contamination. The water contact angle was found to increase with increasing fluorine content and has been attributed to the change of the bonding nature in the films, in particularly increasing CF and CF 2 bonds . Biocompatibility tests performed using MG-63 osteoblast-like cell cultures indicated homogeneous and optimal tissue integration for both the DLC and the F-DLC surfaces. This pulsed-PACVD technique has been shown to produce biocompatible DLC and F-DLC coatings with a potential for large area applications.

The early stages of nucleation and crystallisation of an apatite glass-ceramic: Evidence for nano-scale crystallisation

Crystallisation of a fluorapatite (FAp) (Ca 5(PO 4) 3F) glass-ceramic has been studied by differential scanning calorimetry (DSC), X-ray diffraction (XRD), small angle neutron scattering (SANS), time-of-flight (TOF) neutron diffraction and multinuclear 19F, 31P, 27Al, 29Si magic angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy. During crystallisation of FAp, fluorine is used in forming the FAp phase, since fluorine is known to reduce the glass transition temperature ( T g), the T g of the residual glass increases on FAp crystallisation, which will restrict the growth of the FAp crystals. The XRD patterns of the heat-treated glass show the presence of FAp in addition there is marked line broadening. Debye–Scherrer analysis of the line broadening gives an average crystallite size of approximately 11–21 nm. SANS shows the glass to be single phase with no evidence of amorphous phase separation. SANS analysis of the heat-treated glass shows a single peak at q = 0.036 Å − 1 corresponding to FAp crystallites of about 28 nm. 19F MAS NMR shows a broad resonance identified as F-Ca(n) species in the glass, which narrows down on heat treatment and moves to position close to the F-Ca(3) site in calcium FAp. 31P MAS NMR of the glass showed orthophosphate in structure ( Q 0) with a small amount of pyrophosphate (P-O-P and/or Al-O-P). On heat treatment the resonance narrows and shifts to 2 ppm corresponding to crystalline FAp. MAS NMR data suggests presence of small amount of Mg substituted into the lattice. It is thought that the observation of nano-crystals is aided by the low fluorine content of this glass. We have proposed semi-empirical rules for designing nano-crystalline oxyfluoride phases in glass-ceramic materials.