Freon Research Articles

Effects of Nanotextured PDMS on Cell Culture and Growth

Cell adhesion, morphology and growth are known to be influenced by microscale topography of the surfaces. Taking this a step further, nanotextured polydimethylsiloxane (PDMS) substrates were fabricated by micro reactive ion etching (Micro-RIE). This simple process gave good control on surface texture to improve the affinity of PDMS to enhance cell growth. The effects of various nanoscale roughnesses on cell growth were also quantified. Three different recipes were used to prepare nanotextured PDMS by micro-RIE using oxygen (O2) and carbon tetrafluoride (CF4). First of all etching was performed for 12 min and flow rate of O2 and CF4 was kept at a ratio of 1:1 to fabricate surface 1. Surface 2 was fabricated just by changing the ratio of O2 and CF4 to 1:2. Then the flow rates of gases were kept same as recipe 1 but the etching time was increased to 25 min to prepare surface 3. Next, surface topography of these PDMS substrates was evaluated quantitatively by measuring root mean square surface roughness using an atomic force microscope (AFM). The measured average roughness of three nanotextured PDMS surfaces were found 242.92±87.709 nm, 515±102.28 nm and 629.17±109.67 nm for surface 1, surface 2 and surface 3 respectively. The roughnesses of three types of nanotextured surfaces showed a correlation on cell growth. The cell growth rate on flat PDMS surfaces is known to be very low but nanotextured PDMS surfaces allowed exciting cell growth for three different types of cells (human glioblastoma (hGBM), astrocytesand fibroblast cells).The cells were seeded on various surfaces coated with laminin and incubated for 3 days at 37oC. The cell densities of experimental surfaces were calculated from their images using ImageJ software. For all types of cells, growth was higher on nantoextured PDMS surfaces compare to flat PDMS surface and surface 3 exhibited highest cell density among three nanotextured surfaces. However density of astrocytes cells was 114 ± 16.15 cells per mm2 in surface 3 where as flat PDMS had only 28 ± 3.58 cells per mm2. But standard well plate had higher cell density compare to surface 3 and it was 140 ± 18.07 cells per mm2. Again density of fibroblasts cells in surface 3 was 272.80 ± 13.68 cells per mm2 which was higher compare to flat PDMS but lower than standard well plate. On the other hand surface 3 exhibited very similar cell density as standard well plate for hGBM cells and cell densities were 346 ± 70.64 cells per mm2 and 334.67 ± 63.23 cells per mm2 respectively. Consequently it can be deduced that cell growth strongly depends on surface nanotexturing. By comparing three nanotextured surfaces it was found that surface 1 exhibited lowest roughness compare to surface 2 and surface 3. Therefore available surface area for laminin attachment was lowest in this surface. But surface 2 and surface 3 had higher roughness and therefore provided larger surface area to attach more laminin. As cell growth is a direct function to available laminin attached in the surface therefore cell density was more in later surfaces. In addition to that circulating tumor cells (CTCs) are known to have very high affinity towards nanotextured surfaces. Therefore density of only hGBM cells in nanotextured surface was very similar to cell density in standard well plate. As a result nanotextured PDMS may be thus useful for cancer cytology devices, especially to culture isolated CTCs for further investigation in microfluidic platforms.

Velocity slice imaging study on dissociative electron attachment to CF4

A Velocity Slice Imaging (VSI) study on Dissociative Electron Attachment (DEA) to carbon tetrafluoride, CF4, is presented. Two fragments are observed; F− produced from two, partly overlapping, resonances and CF3 − deriving from a single resonance. The angular distributions of these anionic fragments and their kinetic energy distributions are reported and are then discussed in context of the influence of the Jahn-Teller effect on the symmetry of the resonant states involved.

Catalytic decomposition of CF4 over iron promoted mesoporous catalysts.

A series of mesoporous catalysts (MCM-41) promoted by iron nanoparticles were prepared by the co-precipitation method and tested for the decomposition of carbon tetrafluoride (CF4). The addition of iron oxide nanoparticles to MCM-41 led to an improvement in the catalytic activity for CF4 decomposition. The catalyst was the most active around 5 wt% iron added to MCM-41. Methods of X-ray Powder Diffractometer, Scanning Electron Microscope-Energy Dispersive Spectrometer, BET, and high resolution transmission electron microscopy were used to characterize the MCM-41 catalysts. The analytical results indicated that the addition of over 2 wt% iron nanoparticles increased the surface area of MCM-41, which was the rate-determining factor of CF4 decomposition over MCM-41 catalyst. In conclusion, the addition of iron was responsible for the enhancement of catalytic activity of MCM-41.

Hydrophobic modification of polyethylene terephthalate using nanosecond-pulse dielectric barrier discharge

Compared to the traditional method for surface treatment, non-thermal plasmas have advantages such as low pollution, simple process and low cost. In the paper, non-thermal plasmas are generated by dielectric barrier discharge (DBD) excited by China-made nanosecond-pulse generator with a rise time of ~70 ns and a full width at half maximum of ~100 ns. Such plasmas are used to modify the hydrophobic of the surface of polyethylene terephthalate (PET) in atmospheric carbon tetrafluoride (CF4). The static water contact angle of the PET surface is measured before and after treatment. The effects of CF4 flow, applied voltage, treatment time and CF4 ratio on modification performance are presented. The results show that the hydrophobic of the PET surface can be achieved using DBD plasmas. The static water contact angle of the PET surface can be up to 100 from 66.

Wettability of Plasma-Treated Fibers of Anahaw (<i>Livistona rotundifolia</i>), Buri (<i>Corypha elata</i>) and Pandan (<i>Pandanus amaryllifolius</i>)

Anahaw (Livistona rotundifolia), Buri (Corypha elata) and Pandan (Pandanus amaryllifolius) leaves were plasma-treated using argon, oxygen and carbon tetrafluoride (CF4) gas under varying discharge currents (5 mA, 10 mA, 20 mA and 30 mA) for 15 minutes. The wettability properties of the plasma-treated samples were investigated using the sessile drop method to determine static contact angles on the surfaces. Based on the results, it was observed that increasing the discharge current in argon and oxygen plasma treatment was found to increase the wettability of the three samples while it decreased the wettability of Pandan and Buri samples for carbon tetrafluoride plasma.

Polyurethane microfibrous mat templated polypyrrole: Preparation and biomimetic reactive sensing capabilities

The reactivity of conducting polymers can be exploited to generate new sensors of their working conditions. Here, we verified that the reactive (redox) nature of a chemically generated polypyrrole (PPy) on a polyurethane (PU) microfibrous mat senses the surrounding (physical and chemical) conditions. The (PU/PPy) microfibrous mat was obtained by in situ chemical polymerization of pyrrole from aqueous medium using tetra fluoromethane sulfonate as dopant and a polyurethane microfibrous mat, produced by electrospinning of a PU solution, as template. SEM images showed the homogenous growth of nanostructured PPy on each fiber of the PU microfibrous mat. The cyclic voltammogram (CV) revealed an oxidation peak at 0.22V and a reduction peak at −0.08V vs Ag/AgCl, indicating that the electrochemical activity of the material is imparted by PPy component. Sensing abilities with regard to the surrounding conditions were monitored through chronopotentiometric (CP) responses between two defined oxidation states. The consumed electrical energy during the electrochemical reactions was a linear function of the applied currents or of the working temperature (the reaction material is a current sensor and a temperature sensor) and a semi-logarithmic dependence of the electrolyte concentration (concentration sensor). These sensing abilities are explained on the basis of recently developed theories on the reactivity of conducting polymers.

Spectrometric monitoring of atmospheric carbon tetrafluoride (CF<sub>4</sub>) above the Jungfraujoch station since 1989: evidence of continued increase but at a slowing rate

Abstract. The long-term evolution of the vertical column abundance of carbon tetrafluoride (CF4) above the high-altitude Jungfraujoch station (Swiss Alps, 46.5° N, 8.0° E, 3580 m a.s.l.) has been derived from the spectrometric analysis of Fourier transform infrared solar spectra recorded at that site between 1989 and 2012. The investigation is based on a multi-microwindow approach, two encompassing pairs of absorption lines belonging to the R-branch of the strong ν3 band of CF4 centered at 1283 cm−1, and two additional ones to optimally account for weak but overlapping HNO3 interferences. The analysis reveals a steady accumulation of the very long-lived CF4 above the Jungfraujoch at mean rates of (1.38 ± 0.11) × 1013 molec cm−2 yr−1 from 1989 to 1997, and (0.98 ± 0.02) × 1013 molec cm−2 yr−1 from 1998 to 2012, which correspond to linear growth rates of 1.71 ± 0.14 and 1.04 ± 0.02% yr−1 respectively referenced to 1989 and 1998. Related global CF4 anthropogenic emissions required to sustain these mean increases correspond to 15.8 ± 1.3 and 11.1 ± 0.2 Gg yr−1 over the above specified time intervals. Findings reported here are compared and discussed with respect to relevant northern mid-latitude results obtained remotely from space and balloons as well as in situ at the ground, including new gas chromatography mass spectrometry measurements performed at the Jungfraujoch since 2010.

Fabrication of Carbon Nanodot Arrays with a Pitch of 20 nm for Pattern-Transfer of PDMS Self-Assembled Nanodots

We investigated the fabrication of self-assembled nanodot array using poly (styrene)-poly (dimethyl-siloxane) (PS-PDMS) block copolymer and its transfer technique as a promising method to fabricate magnetic nanodot arrays for ultrahigh density recording. A carbon (C) layer with a high etch-resistance was especially adopted for magnetic nanodot fabrication. We fabricated PDMS nanodot using PS-PDMS block copolymer with a molecular mass of 11,700-2,900 g/mol. The nanodots were first transferred into silicon (Si) layer and then into C layer on Si substrate by carbon tetrafluoride (CF4) and oxygen (O2) reactive ion etching (RIE), respectively. We succeeded in fabricating C nanodots with a diameter of 10 nm and an average pitch of 20 nm.

A new purge and trap headspace technique to analyze low volatile compounds from fluid inclusions of rocks and minerals

A new method for the analysis of trace gases from fluid inclusions of minerals has been developed. The purge and trap GC–MS system is based on the system described by Nolting et al. (1988) and was optimized for the analyses of halogenated volatile organic compounds (VOCs) having boiling points as low as −128°C (carbon tetrafluoride).The sample preconcentration cold trap consists of a U-shaped glass lined steel tube (GLT™), that is immersed into a small liquid nitrogen Dewar vessel for cooling. A rapid desorption step heats up the preconcentration tube in <30s from −196°C to 200°C. The process is carried out by using a pressurized air stream to dissipate the liquid nitrogen followed by resistive heating of the trap. The design of the cold trap and the direct transfer of desorbed analytes onto the GC column via a deactivated capillary column retention gap made sample refocusing within the GC oven unnecessary. Furthermore, a special air-tight grinding device was developed in which samples ranging from soft halite (hardness 2, Mohs scale) to hard quartz (hardness 7) are effectively ground to average diameters of 1000nm or below, thereby releasing gases from fluid inclusions of minerals. The gases are then purged from the grinding chamber with a He carrier gas flow. The detection and quantitative determination of gases, such as SF6 and CF4 released from fluorites and CH3Cl from halite samples is demonstrated.

Investigation on critical breakdown electric field of hot sulfur hexafluoride/carbon tetrafluoride mixtures for high voltage circuit breaker applications

Sulfur hexafluoride (SF6) gas, widely used in high-voltage circuit breakers, has a high global warming potential and hence substitutes are being sought. The use of a mixture of carbon tetrafluoride (CF4) and SF6 is examined here. It is known that this reduces the breakdown voltage at room temperature. However, the electrical breakdown in a circuit breaker after arc interruption occurs in a hot gas environment, with a complicated species composition because of the occurrence of dissociation and other reactions. The likelihood of breakdown depends on the electron interactions with all these species. The critical reduced electric field strength (the field at which breakdown can occur, relative to the number density) of hot SF6/CF4 mixtures corresponding to the dielectric recovery phase of a high voltage circuit breaker is calculated in the temperature range from 300 K to 3500 K. The equilibrium compositions of hot SF6/CF4 mixtures under different mixing fractions were determined based on Gibbs free energy minimization. Full sets of improved cross sections for interactions between electrons and the species present are presented. The critical reduced electric field strength of these mixtures was obtained by balancing electron generation and loss mechanisms. These were evaluated using the electron energy distribution function derived from the Boltzmann transport equation under the two-term approximation. The result indicates that critical electric field strength decreases with increasing heavy-particle temperature from 1500 to 3500 K. Good agreement was found between calculations for pure hot SF6 and pure hot CF4 and experimental results and previous calculations. The addition of CF4 to SF6 was found to increase the critical reduced electric field strength for temperatures above 1500 K, indicating the potential of replacing SF6 by SF6/CF4 mixtures in high-voltage circuit breakers.

High Polarization and Low-Repulsion ${\rm HfO}_{2}$ Thin Film for Alkali Metal Ion Detections by Plasma System With a Complementary Filter

A new plasma system with a complementary filter for low-damage carbon tetrafluoride $({\rm CF}_{4})$ plasma treatment is proposed to incorporate fluorine (F) atoms into a hafnium dioxide $({\rm HfO}_{2})$ thin-film sensing membrane in an electrolyte-insulator-semiconductor structure for alkali metal ion ( ${\rm Na}^{+}$ and ${\rm K}^{+}$ ) detection. Hf 4f and F 1s X-ray photoelectron spectra confirmed the incorporation of fluorine (F) atoms into the ${\rm HfO}_{2}$ sensing membrane after low-damage ${\rm CF}_{4}$ plasma treatment. As the duration of the plasma treatment is increased, the F 1s intensity and the amount of Hf–F bonds increased, and the corresponding ${\rm Na}^{+}$ and ${\rm K}^{+}$ sensitivities drastically increased (pNa: 121.6 mV/pNa; pK: 98.1 mV/pK). The super-Nernst phenomenon is attributed not only to the formation of higher dipole property between Hf and F than that between Hf and O but also to the reduction of plasma bombardment and UV irradiation, which damage the ${\rm HfO}_{2}$ sensing membrane. A positive charge model is proposed to explain the improvements by fluorine incorporation with complementary filter.

Development of textured ZnO-coated low-cost glass substrate with very high haze ratio for silicon-based thin film solar cells

Zinc oxide (ZnO) films with a very high haze ratio and low resistivity were developed on soda–lime glass substrate by using reactive ion etching (RIE) treatment with carbon tetrafluoride (CF4) to modify the substrate surface morphology before the deposition of ZnO films. We found that the surface morphology of the ZnO films deposited by metal organic chemical vapor deposition (MOCVD) technique could be modified by varying the glass treatment conditions and the gas pressure was a key parameter. With increasing glass-etching pressure, the surface morphology of the ZnO films changed from conventional pyramid-like single texture to greater cauliflower-like double texture, leading to significant increases in root mean square roughness and haze ratio of the films. By employing the developed high-haze ZnO films as a front transparent conductive oxide (TCO) layer in microcrystalline silicon solar cells, an enhancement in the quantum efficiency in the long-wavelength region has been achieved. Experimental results have verified that our unique and original glass etching treatment is a simple and effective technique to improve the light-scattering properties of the ZnO films while preserving their good transparency and electrical properties. Thus, the ZnO films deposited on etched soda–lime glass have a high potential for the use as a front TCO layer in thin-film Si solar cells.

High-Pressure Study of Ion-Molecule Reactions in the Mixture of Carbon Tetrafluoride and Argon

Charge-exchange ion molecule reactions of Ar ions with CF4 have been studied in the pressure range 1.33 39.99 Pa. A quadrupole mass spectrometer with a high-pressure ion source has been used for measuring gaseous ion molecule reactions in the mixture of 1% CF4 and 99% Ar. The fractional abundance Ii/ ∑ Ii of the observed CF+3 , CF + 2 and argon ions has been determined as a function of the gas mixture pressure (at the values of the repeller electrode potentials VR ranging from 2 to 10 V).

SAFT-γ Force Field for the Simulation of Molecular Fluids: 2. Coarse-Grained Models of Greenhouse Gases, Refrigerants, and Long Alkanes

In the first paper of this series [C. Avendaño, T. Lafitte, A. Galindo, C. S. Adjiman, G. Jackson, and E. A. Müller, J. Phys. Chem. B2011, 115, 11154] we introduced the SAFT-γ force field for molecular simulation of fluids. In our approach, a molecular-based equation of state (EoS) is used to obtain coarse-grained (CG) intermolecular potentials that can then be employed in molecular simulation over a wide range of thermodynamic conditions of the fluid. The macroscopic experimental data for the vapor-liquid equilibria (saturated liquid density and vapor pressure) of a given system are represented with the SAFT-VR Mie EoS and used to estimate effective intermolecular parameters that provide a good description of the thermodynamic properties by exploring a wide parameter space for models based on the Mie (generalized Lennard-Jones) potential. This methodology was first used to develop a simple single-segment CG Mie model of carbon dioxide (CO2) which allows for a reliable representation of the fluid-phase equilibria (for which the model was parametrized), as well as an accurate prediction of other properties such as the enthalpy of vaporization, interfacial tension, supercritical density, and second-derivative thermodynamic properties (thermal expansivity, isothermal compressibility, heat capacity, Joule-Thomson coefficient, and speed of sound). In our current paper, the methodology is further applied and extended to develop effective SAFT-γ CG Mie force fields for some important greenhouse gases including carbon tetrafluoride (CF4) and sulfur hexafluoride (SF6), modeled as simple spherical molecules, and for long linear alkanes including n-decane (n-C10H22) and n-eicosane (n-C20H42), modeled as homonuclear chains of spherical Mie segments. We also apply the SAFT-γ methodology to obtain a CG homonuclear two-segment Mie intermolecular potential for the more challenging polar and asymmetric compound 2,3,3,3-tetrafluoro-1-propene (HFO-1234yf), a novel replacement refrigerant with promising properties. The description of the fluid-phase behavior and the prediction of the other thermophysical properties obtained by molecular simulation using our SAFT-γ CG Mie force fields are found to be of comparable quality (and sometimes superior) to that obtained using the more sophisticated all-atom (AA) and united-atom (UA) models commonly employed in the field. We should emphasize that though the focus of our current work is on simple homonuclear models, the SAFT-γ methodology is based on a group contribution methodology which is naturally suited to the development of more sophisticated heteronuclear models.

Negative ion formation through dissociative electron attachment to the group IV tetrafluorides: Carbon tetrafluoride, silicon tetrafluoride and germanium tetrafluoride

Dissociative electron attachment (DEA) to the group IV tetrafluorides: CF4, SiF4 and GeF4, is reported in the incident electron energy range from about 0 to 14eV. The F2− formation from CF4 is established and the appearance energies (AEs) for F−, CF3− and F2− are determined using a three-point calibration for the energy scale. These are found to be 4.7±0.1eV, 4.5±0.1eV and 5.6±0.1eV, respectively. For SiF4 the AEs for F−, SiF3− and F2−, through the dominating resonance are found to be 10.2±0.1eV, 10.2±0.1eV and 10.3±0.1eV, respectively. From GeF4 the molecular ion GeF4− and the fragments GeF3−, GeF2−, GeF− and F− are all observed with appreciable intensities, and the F− production is found to be significantly close to 0eV incident electron energy. The present findings are compared with earlier experiments and discussed in context to the thermochemistry of the respective processes as well as the nature of the underlying resonances.

Determination of Electron Swarm Parameters in Pure CHF3 and CF4 by a Time-Resolved Method

The density-normalized effective ionization coefficient (α − η)/N (α and η are the ionization and attachment coefficients respectively), the electron drift velocity Ve and density-normalized longitudinal diffusion coefficient NDL in trifluoromethane (CHF3) and carbon tetrafluoride (CF4) were measured using a pulsed Townsend technique over a wide E/N range. From the plots of (α − η)/N, we have derived the limiting field strength, (E/N)lim, which is valid for the analysis of insulation characteristics and applications to power equipment. Comparisons of the electron swarms parameters between CHF3 and CF4 have been performed, and the global warming potential (GWP) is also taken into account.

Orientation Effect in the Low‐Energy Electron Attachment to the Apolar Carbon Tetrafluoride Molecule

Orientation Effect in the Low‐Energy Electron Attachment to the Apolar Carbon Tetrafluoride Molecule

Effect of counterions on hypervalent interactions in prereaction complexes of S N 2 reactions of bisphenoid compounds of the second and third period elements

The electronic and molecular structures of the (LiF)nXFm complexes (X = C, N, O, F, Si, P, S, Cl; m = 1–4, n = 0, 1, 3) were studied by the ab initio (MP2(full)/6-311+G*) and density functional theory (B3LYP/6-311+G*) methods. All bisphenoid anionic structures XFm− (X = C, N, O, F, Si, P, S, Cl; m = 2–5) of elements of the second and third periods, except carbon fluorides, are most stable in the hypervalent state of atoms with strongly elongated axial bonds. Carbon tetrafluoride forms a stable intermolecular F−...CF4 complex. In all cases of addition of the Li atom as a counterion, the most stable intermolecular complex of lithium fluoride with fluorides of elements is stabilized by the hypervalent interaction. In all cases when the counterion is complicated to lithium trifluoride, except for (LiF)3CF4 and (LiF)3NF3, the hypervalent structure with equal and elongated X-F axial bonds is stabilized. In the cases of the (LiF)3CF4 and (LiF)3NF3 complexes, the prereaction structures bound by the strong hypervalent interaction are stabilized.

Improved water repellency of black spruce wood surfaces after treatment in carbon tetrafluoride plasmas

Plasma treatments for black spruce wood (Picea mariana (Mill.) B.S.P.), a widespread forest species from Canada, were carried out in order to waterproof the exposed surfaces. Experiments were performed using inductively coupled argon plasma with carbon tetrafluoride as the gaseous precursor for plasma-enhanced chemical vapor deposition of functional fluoropolymer coatings on wood. Analysis of the wettability through water contact angle measurements showed water-repellent characteristics, with static contact angles up to 130° depending on plasma exposure time, CF4 concentration in the Ar/CF4 plasma, and plasma source-to-substrate distance. X-ray photoelectron spectroscopy investigations of plasma-treated wood surfaces confirmed the growth of a thin, fluorocarbon layer with fluorine atomic concentrations close to 50 % on highly hydrophobic wood surfaces. Estimation of the thickness of the coatings by stylus profilometry revealed that a minimum layer thickness of about 80 nm is required to obtain water repellant wood surfaces with minimum water uptake. This complete set of data indicates that fluorocarbon-containing plasmas represent a very promising approach for improving the durability of wood products in wet and humid conditions.

Effect of the molecular interactions on the separation of nonpolar mixtures using Cu-BTC metal–organic framework

We report an investigation on the adsorption of nonpolar molecules using the copper(II) benzene-1,3,5-tricarboxylate metal–organic framework (Cu-BTC) by means of molecular simulations. This metal–organic framework is formed by small, tetrahedral cages of 5Å in diameter and by large cages of 11 and 13Å in diameter. We focus on the effect that the molecular interactions adsorbents–adsorbates and adsorbates–adsorbates exert on the adsorption that takes place inside the tetrahedral cages. The study is carried out for simple gases modeled as spherical pseudoatoms and for their mixtures. These mixtures are composed by molecules of argon – that are accessible to the tetrahedral cages – and by hypothetic molecules with sigma Lennard–Jones parameters that span from 3.6Å (sigma defined for the molecule of argon) to 4.66Å (sigma defined for the molecule of carbon tetrafluoride). When the value of sigma is low enough to allow the molecule to enter the tetrahedral cages, we observe that it competes with argon for the adsorption in these cavities. This competition is enhanced for the molecules with the largest values of the sigma Lennard–Jones parameter.