Plasma fluorination of polystyrene

ESCA and contact-angle measurements were used to characterize the surfaces of polystyrene films exposed to SF₆, CF₄, and C₂F₆ plasmas. SF₆ plasmas cause loss of aromaticity in the polystyrene surface region via saturation of the phenyl ring and/or carbon-bond breakage and subsequent fluorination. C₂F₆ plasmas graft CF_x radicals directly to the polystyrene surface without necessarily destroying the aromaticity of the polymer. CF₄ plasmas appear to be intermediate in character between SF₆ and C₂F₆ plasmas.     

Plasma fluorination of polyolefins

ESCA and contact angle measurements were used to characterize the surfaces of Polyethylene and polypropylene films exposed to SF₆, CF₄, and C₂F₆ plasmas. None of these gases polymerized in the plasma. However, all plasma treatments grafted fluorinated functionalities directly to the polymer surfaces. SF₆ plasmas graft fluorine atoms to a polyolefin surface. CF₄ plasmas also react by a mechanism dominated by fluorine atoms, but with some contribution from CF_x-radical reactions. Although C₂F₆ does not polymerize, the mechanism of grafting is still dominated by the reactions of CF_x radicals. For all gases studied, the lack of polymerization is attributed to competitive ablation and polymerization reactions occurring under conditions of ion bombardment.     

Hierarchical Pore Development by Plasma Etching of Zr‐Based Metal–Organic Frameworks

The typically stable Zr‐based metal–organic frameworks (MOFs) UiO‐66 and UiO‐66‐NH₂ were treated with tetrafluoromethane (CF₄) and hexafluoroethane (C₂F₆) plasmas. Through interactions between fluoride radicals from the perfluoroalkane plasma and the zirconium–oxygen bonds of the MOF, the resulting materials showed the development of mesoporosity, creating a hierarchical pore structure. It is anticipated that this strategy can be used as a post‐synthetic technique for developing hierarchical networks in a variety of MOFs.     

Fundamental aspect and behavior of saturated fluorocarbons in glow discharge in absence of potential source of hydrogen

The glow discharge of a series of saturated fluorocarbons, C_nF_2n+2 (n = 1, 2, 4, 6, and 8), was studied with glass substrates which do not contain any hydrogen. It was found that the deposition rate was a function of the F/C ratio of the starting fluorocarbons. That is, fluorocarbons with higher F/C ratio, such as CF₄ and C₂F₆, hardly polymerized, while fluorocarbons with lower F/C ratio, such as C₈F₁₈, polymerized as well as C₂F₄. After plasma exposure, the surface of glass substrate was characterized by measurements of water contact angle, water droplet rolling-off angle, and ESCA. Although all saturated fluorocarbon plasmas could alter the surface more hydrophobic than before, the deposited materials from fluorocarbons with higher F/C were not stable. Also, in plasmas with high F/C fluorocarbons, i.e., CF₄ and C₂F₆, sputtering of the electrode material was observed. © 1992 John Wiley & Sons, Inc.     

Rate Coefficient for Self-Association Reaction of CF2 Radicals Determined in the Afterglowof Low-Pressure C4F8 Plasmas

We have analyzed decay kinetics of CF₂ radicals in the afterglow of low-pressure, high-density C₄F₈ plasmas. The decay curve of CF₂ density has been approximated by the combination of first- and second-order kinetics. The surface loss probability evaluated from the frequency of the first-order decay process has been on the order of 10^–4. This small surface loss probability has enabled us to observe the second-order decay process. The mechanism of the second-order decay is self-association reaction between CF₂ radicals (CF₂+CF₂C₂F₄). The rate coefficient for this reaction has been evaluated as (2.6–5.3)×10^–14 cm³/s under gas pressures of 2 to 100 mTorr. The rate coefficient was found to be almost independent of the gas pressure and has been in close agreement with known values, which are determined in high gas pressures above 1 Torr.     

Experimental Study of Capacitive RF <Emphasis Type="Italic">c</Emphasis>-C<Subscript>4</Subscript>F<Subscript>8</Subscript> Discharge with Synchrotron Vacuum Ultraviolet Photoionization Mass Spectrometry

Capacitive radio frequency (RF) discharge of c-C₄F₈ (octafluorocyclobutane) has been studied with synchrotron vacuum ultraviolet (SVUV) photoionization mass spectrometry (PIMS) at 4 Torr and 33.33 kHz. Various free radicals and reactive intermediates have been identified through measurement of photoionization mass spectra and photoionization efficiency (PIE) spectra. CF₂=CF₂ is main product in the plasma, indicating that the dissociation of c-C₄F₈ into CF₂=CF₂ is one of prominent reactions in the present experimental conditions. The observation of large species including C₅F₈, C₅F₁₀ and C₆F₁₀ is presented in our work. Besides, the dependences of the signals of neutral species in the discharge of c-C₄F₈ on RF power are presented in this paper.     

The photolysis of pentafluoroacetone

The photolysis of pentafluoroacetone has been investigated in the 3130 Å region, from room temperature to 360°C. The Φ_CO varies from 0.7 to 0.9 over this range, and the decomposition is represented by CF₂HCOCF₃ → CF₂H + CO + CF₃. The disproportionation/combination ratio for CF₃ and CF₂H (→ CF₃H + CF₂) radicals is found to be 0.09. Arrhenius parameters for hydrogen atom abstraction from the ketone are log₁₀A = 12.7 (units are mole^?1 cc sec^?1) and E = 14.3 kcal mole^?1 for CF₂H, and log₁₀A = 12.1 and E = 11.8, for CF₃ radicals. At low pressures HF elimination reactions are observed from the vibrationally excited fluoroethanes, C₂F₅H* and C₂F₄H₂*, formed in the system. A rough estimate of the activation energy for the process C₂F₅H → C₂F₄ + HF of 60–65 kcal mole^?1 is made.     

Original fluorinated surfactants potentially non-bioaccumulable

This minireview updates non-exhaustive recent strategies of synthesis of original fluorosurfactants potentially non-bioaccumulable. Various strategies have been focused on (i) the preparation of CF₃–X–(CH₂)_n–SO₃Na (with X = O, C₆H₄O or N(CF₃) and n = 8–12), (ii) the oligomerization of hexafluoropropylene oxide (HFPO) to further synthesize oligo(HFPO)–CF(CF₃)CO–R_H (where R_H stands for an hydrophilic chain); (iii) the telomerization of vinylidene fluoride (VDF) with 1-iodopentafluoroethane or 1-iodononafluorobutane to produce C_nF_2n+1–(VDF)₂–CH₂CO₂R (n = 2 or 4, R = H or NH₄), (iv) the radical telomerization of 3,3,3-trifluoropropene (TFP) with isoperfluoropropyliodide or diethyl hydrogenophosphonate to prepare (CF₃)₂CF(TFP)_x–R_H or CF₃–CH₂–CH₂–(TFP)_y–P(O)(OH)₂, and (v) the radical cotelomerization of VDF and TFP, or their controlled radical copolymerization in the presence of (CF₃)₂CFI or a fluorinated xanthate. In most cases, the surface tensions versus the surfactant concentrations have been assessed. These above strategies led to various highly fluorinated (but yet not perfluorinated) telomers whose chemical changes enabled to obtain original surfactants as novel alternatives to perfluorooctanoic acid (PFOA), ammonium perfluorooctanoate (APFO), or perfluorooctylsulfonic acid (PFOS) regarded as bioaccumulable, persistent, and toxic.     

Disproportionation-combination rate constant ratios for haloalkyl radicals: Evidence for heterogeneous disproportionation

Disproportionation-combination rate constant ratios, k_d/k_c, have been determined for R + RCH₂CHCl and for the auto disproportionation-combination of RCH₂CHCl radicals, R = CF₃, C₂F₅, and C₃F₇. The k_d/k_c for R = CF₃ and to a lesser degree for R = C₂F₅ and C₃F₇ were very sensitive to the surface/volume ratio of the reaction vessel suggesting a heterogeneous component for disproportionation.     

Insertion reactions of difluorocarbene generated by pyrolysis of hexafluoropropene oxide to OH bond

ROCHF₂-type fluorinated ethers were synthesized by the reaction of hexafluoropropene oxide (HFPO) with alcohol or phenol. In this reaction, although the insertion reaction of difluorocarbene to OH bond and the nucleophilic attack of alcohol or phenol to HFPO were competition, the insertion reaction proceeded predominantly to give fluorinated ether in the case of low nucleophilic alcohol or phenol. In addition, high reaction pressure is advantageous to the selectivity of the fluorinated ethers in the reaction of HFPO with (CF₃)₂CHOH or C₆F₅OH.     

The dark reactions F2 + CF3I,C2F5I,and n-C3F7I

The reactions between F₂ and the lowest members of the homologous series of perfluoroalkyl iodides (CF₃I, C₂F₅I, and n-C₃F₇I) have been studied. For these compounds, an exponential decrease in the alkyl iodide concentration over time following an induction period is observed for certain experimental conditions. Other conditions lead to chaotic-like kinetic behavior where the rate of alkyl iodide consumption continually changes. Kinetic rate data with CF₃I show that the disappearance rate depends upon both the type of surface and surface preparation. For all three compounds, Arrhenius plots reveal activation energies on the order of 10 kcal/mol, consistent with effective initiation steps of F₂ + RI → RIF + F, where R represents the CF₃, C₂F₅, or n-C₃F₇ radical respectively. The end products of the F₂ + RI reactions are RF, R₂, and IF₅, suggesting that the R radicals play an important kinetic role. Introducing O₂ into the F₂ + RI reaction systems results in successive oxidation of R by O₂, leading to the formation of CF₂O as an additional end product. IF(B → X) emission is observed from the RI-rich F₂ + RI reactions, confirming the existence of IF as an intermediate. © 1996 John Wiley & Sons, Inc.     

Penetration of plasma surface modification into porous media. III. Multiple samples exposed to CF4 and C2F4 low temperature cascade arc torch

The depth and possible mechanisms of the penetration of surface modification into porous media by a low temperature cascade are torch are investigated. Two different modes of such penetration (“flow controlled” and “diffusion controlled”) are evaluated. Three porous samples [stacks of 10 sheets of nonwoven fabrics of poly(ethylene terephthalate)each], placed at an axial distance of 24, 28, and 32 cm from the cascade are anode, are exposed to a low temperature cascade arc torch containing argon and CF₄ or C₂F₄, and surface properties of each of the sheets within treated porous samples are examined by ESCA. It is shown that interaction of chemically reactive species, created in the low temperature cascade arc torch, with the surface is not limited to the surface directly contacted by the torch. The flow controlled penetration is more pronounced for the outer layers, while diffusion controlled penetration is within the inner layers of the porous structure. Substantial differences in the fluorination effect of CF₄ (nonpolymer forming gas) and C₂F₄ (polymer forming gas) discharges for the second and third stacks are observed, that can be explained by the fact that the major effect of the CF₄ cascade arc torch treatment is based on the reaction of reactive species with the surface polymer molecules. The effect of C₂F₄ cascade arc torch treatment is based on the reactions of reactive species with polymers as well as reactions of reactive species themselves at the surface (plasma polymerization). Reactivity of the species created in C₂F₄ discharge is much higher compared to that created in CF₄ discharge, which is one of the major factors influencing penetration trends of low temperature cascade arc treatment into porous media. © 1995 John Wiley & Sons, Inc.     

Gas phase radiation chemistry of hexafluoroethane

The Co-60 gamma radiolysis of gaseous C₂F₆ was investigated at 50 Torr pressure, both pure and with 10% oxygen added. For the pure system, the radiolytic products and their respective C values were CF₄, 2.27; C₃F₈, 0.23; C₄F₁₀, 0.09; C₅F₁₂, 0.015; and C₆F₁₄, 0.009. All radiolysis products except for CF₄ (C = 0.61) were eliminated when 10% O₂ was added as scavenger. The results are discussed mainly in terms of the decomposition of excited C₂F₆ into free radicals, which can then combine. The unscavenged CF₄ is accounted for by the ion-molecule reaction CF₃⁺ + C₂F₆ → CF₄ + C₂F₅⁺.     

Molecular structures of 3‐[(2,2,3,3‐tetrafluoropropoxy)methyl]‐ and 3‐[(2,2,3,3,3‐pentafluoropropoxy)methyl]pyridinium saccharinates

The salts 3‐[(2,2,3,3‐tetrafluoropropoxy)methyl]pyridinium saccharinate, C₉H₁₀F₄NO⁺·C₇H₄NO₃S⁻, (1), and 3‐[(2,2,3,3,3‐pentafluoropropoxy)methyl]pyridinium saccharinate, C₉H₉F₅NO⁺·C₇H₄NO₃S⁻, (2), i.e. saccharinate (or 1,1‐dioxo‐1λ⁶,2‐benzothiazol‐3‐olate) salts of pyridinium with –CH₂OCH₂CF₂CF₂H and –CH₂OCH₂CF₂CF₃meta substituents, respectively, were investigated crystallographically in order to compare their fluorine‐related weak interactions in the solid state. Both salts demonstrate a stable synthon formed by the pyridinium cation and the saccharinate anion, in which a seven‐membered ring reveals a double hydrogen‐bonding pattern. The twist between the pyridinium plane and the saccharinate plane in (2) is 21.26 (8)° and that in (1) is 8.03 (6)°. Both salts also show stacks of alternating cation–anion π‐interactions. The layer distances, calculated from the centroid of the saccharinate plane to the neighbouring pyridinium planes, above and below, are 3.406 (2) and 3.517 (2) Å in (1), and 3.409 (3) and 3.458 (3) Å in (2).     

Surface modification of ethylene‐co‐tetrafluoroethylene films by remote plasmas

The surface modifications of ethylene‐co‐tetrafluoroethylene (ETFE) surfaces by six plasmas (direct H₂, Ar, and O₂ plasmas and remote H₂, Ar, and O₂ plasmas) were investigated with two questions in mind: (1) what plasma could effectively modify ETFE surfaces and (2) which of the CF₂? CF₂ and CH₂? CH₂ components in ETFE was selectively modified? The plasma exposure led to a weight loss from the ETFE surfaces and changes in the chemical composition on ETFE surfaces. The weight‐loss rate showed a strong dependence on what plasma was used for the modification. The remote H₂ plasma led to the lowest rate of weight loss in the six plasma exposures, and the direct O₂ plasma led to the highest rate of weight loss. During exposure to the plasmas, defluorination occurred, and two new C_1s components [? CH₂? CHF? CH₂? and ? CH₂? CH(O? R)? CF_x? , and ? CH₂? CHF? CF₂? , ? CH₂? C(O)? CF_x? , and ? CF_x? C(O)? O? ] were formed on the modified ETFE surfaces. Defluorination was strongly influenced by what plasma was used for the modification. The remote H₂ and Ar plasmas showed high defluorinations of 55 and 51%, respectively. The remote O₂ plasma showed a low defluorination of only 25%. Conclusively, the remote H₂ and Ar plasma exposure effectively modified ETFE surfaces. With the exposure of these surfaces to the remote H₂ plasma, the CF₂? CF₂ component was predominantly modified, rather than the CH₂? CH₂ component. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 2871–2882, 2002     

A study of the deposition of polymeric material onto surfaces from fluorocarbon RF plasmas

A series of fluorocarbon gases, viz., CF₄, C₂F₆, C₃F₈, and CHF₃, have been compared for their relative tendencies to deposit polymeric material onto various surfaces, including Si and SiO₂, under RF plasma conditions. The plasmas were examined by optical emission spectroscopy. C₃F₈ and CHF₃ were found to produce the highest yields of polymers, although these exhibited significant differences in structure (as shown by XPS and IR) and differences in thermal stability, both of which could be minimized by replacing the C₃F₈ gas with a C₃F₈/H₂ mixture. The polymers produced from CHF₃ under the conditions of the present study were found to accumulate preferentially onto Si rather than SiO₂, as verified by the technique of Rutherford backscattering spectrometry.     

Molybdenum(VI) Bis(imido) Complexes: From Frustrated Lewis Pairs to Weakly Coordinating Cations

Molybdenum(VI) bis(imido) complexes [Mo(NtBu)₂(L^R)₂] (R=H 1 a ; R=CF₃ 1 b ) combined with B(C₆F₅)₃ ( 1 a /B(C₆F₅)₃, 1 b /B(C₆F₅)₃) exhibit a frustrated Lewis pair (FLP) character that can heterolytically split H−H, Si−H and O−H bonds. Cleavage of H₂ and Et₃SiH affords ion pairs [Mo(NtBu)(NHtBu)(L^R)₂][HB(C₆F₅)₃] (R=H 2 a ; R=CF₃ 2 b ) composed of a Mo(VI) amido imido cation and a hydridoborate anion, while reaction with H₂O leads to [Mo(NtBu)(NHtBu)(L^R)₂][(HO)B(C₆F₅)₃] (R=H 3 a ; R=CF₃ 3 b ). Ion pairs 2 a and 2 b are catalysts for the hydrosilylation of aldehydes with triethylsilane, with 2 b being more active than 2 a . Mechanistic elucidation revealed insertion of the aldehyde into the B−H bond of [HB(C₆F₅)₃]⁻. We were able to isolate and fully characterize, including by single-crystal X-ray diffraction analysis, the inserted products Mo(NtBu)(NHtBu)(L^R)₂][{PhCH₂O}B(C₆F₅)₃] (R=H 4 a ; R=CF₃ 4 b ). Catalysis occurs at [HB(C₆F₅)₃]⁻ while [Mo(NtBu)(NHtBu)(L^R)₂]⁺ (R=H or CF₃) act as the cationic counterions. However, the striking difference in reactivity gives ample evidence that molybdenum cations behave as weakly coordinating cations (WCC).     

Mechanisms of radical production in CF3Cl,CF3Br,and related plasma etching gases: The role of added oxidants

A model is presented that accounts for the formation of various etchants, unsaturated species, and polymers in halocarbon/oxidant plasma etching mixtures. It is discussed in terms of emission and mass spectral measurements of stable and unstable products in CF₃Cl, CF₃Br, C₂F₆, and related systems. In this reaction scheme, fluorocarbon precursors derived from the building block radical CF₂ are saturated during reactions with atoms and reactive molecules. The most reactive species are preferentially removed by the saturation reactions. An ordering of this reactivity can be used to predict the dominant atomic etchants as a function of halocarbon and additive gas compositions.     

Penetration of plasma surface modification. II. CF4 and C2F4 low-temperature cascade arc torch

The depth of surface modification by low-temperature cascade arc torch is investigated. A stack of 10 sheets of nonwoven fabrics of polyester fibers is exposed to a low-temperature cascade arc torch containing CF₄ or C₂F₄, and the fluorination effect is examined by ESCA. It is shown that interaction of chemically reactive species, created in a low-temperature cascade arc torch, with the surface is not limited to the surface contacted by the torch (flame). The results indicate that the fluorination effect is observed on surfaces which are shadowed from the torch by overlying fibers. The highest degree of fluorination is found on the second layer, rather than on the first layer which the torch contacts directly. No significant differences in the trends of penetration of CF₄ and C₂F₄ treatment through porous samples are observed. However, ESCA data show principal differences in chemical structures of the surfaces treated with CF₄ (nonpolymer-forming gas) and C₂F₄ (polymer-forming gas). These results indicate that chemically reactive species induced by the excited species of argon rather than primary species created by the ionization process seem to play predominant roles in the surface treatment as well as the low-temperature cascade arc torch polymerization of perfluorinated compounds. © 1994 John Wiley & Sons, Inc.     

Disproportionation reactions between alkyl and fluoroalkyl radicals. V. Perfluoro-n-propyl and ethyl radicals revisited

A redetermination of the disproportionation/combination ratio for n–C₃F₇ and C₂H₅ radicals gives a value of Δ(n–C₃F₇, C₂H₅) = 0.13 ± 0.01, independent of the temperature. The radicals were produced by the photolysis of n–C₃F₇COC₂H₅. The previous determinations of this ratio are discussed and are found to be largely incorrect. The values for Δ(CF₃, C₂H₅) and Δ(C₂F₅, C₂H₅) are also re-evaluated, and the recommended values are 0.10 ± 0.02 and 0.12 ± 0.02, respectively. Systems involving perfluoroalkyl and ethyl radicals are complicated due to rapid perfluororadical addition to the ethylene formed in the disproportionation process. The extent of this reaction, and its consequences, are discussed and evaluated. The role of the propionyl (C₂H₅CO) radical in the room temperature photolysis is also assessed. However, it is found that the Δ values determined by the intercept method used in this work are not affected by the secondary reactions that occur. It is concluded that high cross-combination ratios are general to perfluoroalkyl-alkyl radical interactions. For C₃F₇ and C₂H₅ radicals the ratio is 2.7–2.8. Above 100°C ratios exceed 3 due to secondary reactions.