Low surface energy polymeric films from partially fluorinated photocurable solventless liquid oligoesters

Summary We have recently shown that low surface energy polymeric films can be readily obtained from partially fluorinated hydroxyl-end-capped solventless liquid oligoesters by thermal curing [1]. Photocurable liquid oligoesters can be prepared by further substituting the remaining hydroxyl end groups with acrylic double bonds. A conventional photoinitiator containing 2-hydroxy-2-methylpropiophenone was used to cure the liquid oligoesters. As the fluorine content increases from 0 to about 1.57 wt %, the surface energy decreases by about 14 mN/m. The fluorine level in the outer few nanometers is significantly greater than that in the bulk, as revealed by XPS studies. The driving force for the surface segregation of fluorinated species comes from the large difference in surface energy between the oligoesters and their fluorinated counterparts. Received: 14 August 2001/Revised version: 10 October 2001/Accepted: 10 October 2001     

Synthesis and surface characterization of copoly(imide alkyl ether)s containing pendant fluoroalkyl groups

A series of copoly(imide alkyl ether)s were synthesized to explore surface migration of fluorinated alkyl ether blocks (AEFO)s. Mechanical and surface properties of solution cast, thermally imidized films were determined. Incorporation of the AEFO oligomers at loading levels up to 5 wt % resulted in a slight decrease (usually less than 10%) in tensile modulus. Surface migration of the AEFOs raised the advancing water contact angle from approximately 80° to above 95° for the copolymer systems. The composition at which addition of more AEFO further increased water contact angle values was related to the number of fluorine atoms in the perfluorinated side chains. Surface excess concentration of the AEFO at different loading levels was calculated from X‐ray photoelectron spectroscopy results. At higher AEFO loading levels, the surface excess concentration was relatively constant suggesting formation of stable structures within the bulk similar to micelle formation in surfactant solutions. Based on these results, it was determined that surface saturation occurred with the fluorinated AEFO species at loading levels as low as 1 wt % engendering changes in surface properties while retaining the bulk imide properties. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41538.     

Surface modification with waterborne fluorinated anionic polyurethane dispersions

Waterborne fluorinated anionic polyurethane dispersions (FAPUDs) were synthesized from tris(6‐isocyanatohexyl) isocyanurate, N‐ethyl‐N‐2‐hydroxyethyl‐perfluorooctanesulfonamide, poly(oxytetramethylene glycol) (PTMG), dimethylolpropionic acid (DMPA), hexamethylene diisocyanate, 1,4‐butanediol, and two different neutralizing agents (triethylamine and sodium carbonate). Waterborne polyurethane dispersions (PUDs) were synthesized from isophorone diisocyanate, PTMG, DMPA, and ethylenediamine as chain extenders. The particle size of the FAPUDs, based on the fluorine content and degree of neutralization (DN), was measured with dynamic light scattering. So that the surface modification and morphology variations of the PUDs through the addition of the FAPUDs could be observed, the surface energy and thermal properties of the blending films [fluorine PUD mixtures (FPMs)] were measured with contact‐angle analysis and differential scanning calorimetry. The particle size of the FAPUDs increased as the fluorine content in the FAPUDs increased and decreased as the DN increased. The surface energy of the FPM films made from the blending of the FAPUD T series (neutralization with triethylamine) gradually decreased above the critical fluorine concentration (0.02797 wt %). However, for the blending of the FAPUD 25Na series (neutralization with sodium carbonate), the surface energy increased above the critical fluorine concentration (0.02797 wt %) because of the increase in Na salts. The FAPUDs showed the native thermal behavior of the fluorine. However, the thermal properties of the blending films were like those of pure PUDs. This showed that the morphology of the PUDs was rarely unchanged when the FAPUDs were added. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 3322–3330, 2002     

环氧乳液与含氟乳液的拼混研究

运用种子乳液聚合法制备了固含量(固体质量分数)为45%的含氟乳液;运用后乳化法制得了环氧乳液。ATR-FTIR测试表明环氧乳液与含氟乳液进行了有效的拼混。运用KrussK12型动态表面能分析仪测试了含氟涂膜对水和十六烷的接触角,对影响拼混乳液涂膜性能的因素如环氧树脂及其固化剂的比例、氟原子含量、成膜基材材质、成膜温度等进行了探讨研究。结果表明制备的含氟拼混乳液性能良好。     

Wettability of nanocrystalline diamond films

The wettability of nanocrystalline CVD diamond films grown in a microwave plasma using Ar/CH₄/H₂ mixtures with tin melt (250–850 °C) and water was studied by the sessile-drop method. The films showed the highest contact angles θ of 168 ± 3° for tin among all carbon materials. The surface hydrogenation and oxidation allow tailoring of the θ value for water from 106 ± 3° (comparable to polymers) to 5° in a much wider range compared to microcrystalline diamond films. Doping with nitrogen by adding N₂ in plasma strongly affects the wetting presumably due to an increase of sp²-carbon fraction in the films and formation of C–N radicals.     

Studies of dielectric characteristics and surface energies of spin‐coated polyimide films

A two‐step method, that is, polyamic acid formation with subsequent curing, was used to synthesize six kinds of polyimides. Dielectric constants and surface energies were investigated to determine the nature of the fluorinated and nonfluorinated polyimides. The dielectric constant decreased from 3.3 (at 100 kHz) for PMDA/ODA to 2.6 (at 100 kHz) for 6FDA/4,4′‐6F when the fluorine content increased from 0 to 30.7 wt %. Simultaneously, the water contact angle increased from 65° for PMDA/ODA to 78° for 6FDA/4,4′‐6F. Experimental results indicated that fluorinated polyimides contained a lower dielectric constant with improved water resistance. The surface energy values obtained from experiments agreed well with Holmes' correlation between surface energy and dielectric constant. The surface energies and dielectric constants were significantly affected by the polymer backbone structures, especially by the fluorination effect. Therefore, by choosing the appropriate monomers, polyimides of low dielectric constants with hydrophobic surfaces could be obtained. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 1642–1652, 2001     

Selective oxidation of ammonia over copper-silver-based catalysts

A novel catalyst based on copper-silver was developed to solve the contradiction between the high conversion temperature of Cu-based catalyst and low N₂ selectivity of Ag-based catalyst during selective oxidation of ammonium gas. The Cu-Ag-based catalyst (Cu 5 wt.%-Ag 5 wt.%/Al₂O₃) displayed a relatively low complete conversion temperature (<320 °C) with a high N₂ selectivity (>95%). Increasing loading of Cu and Ag decreases N₂ selectivity. The low N₂ selectivity of Ag-based catalyst is possibly related to the formation of Ag₂O crystals. Improvement of N₂ selectivity of Ag-based catalyst was obtained by doping Cu to decrease crystallized Ag₂O phase. The temperature programmed reaction (TPR) data show that N₂O is the main byproduct of oxidation of ammonia at temperature lower than 200 °C. Two bands of nitrate species at 1541 and 1302 cm⁻¹ were observed on Ag 10 wt.%/Al₂O₃ at the temperature higher than 250 °C, which indicates the formation of NO_x during the selective catalytic oxidation of ammonia. No nitrate species was observed on Cu 10 wt.%/Al₂O₃ and Cu 5 wt.%-Ag 5 wt.%/Al₂O₃, while only one nitrate species (1543 cm⁻¹) existed on Cu 10 wt.%-Ag 10 wt.%/Al₂O₃. We proposed that mixing Ag with Cu inhibited the formation of NO_x during the selective catalytic oxidation of ammonia over Cu-Ag/Al₂O₃.     

Origin of transient species present on the surface of a PdO/γ-Al2O3 catalyst during the methane combustion reaction

Operando DRIFTS was applied to the study of the evolution of surface species formed on a Pd (2 wt.%)/γ-Al₂O₃ catalyst in various conditions. No differences were observed as a function of the initial oxidation state of palladium. Formates/carbonates species were identified at low temperature (<400 °C) and disappeared when CO₂ production started. These species come from the Pd-catalyzed interaction of CO with the alumina support, while CO₂ induces hydrogenocarbonates formation at low temperature (<300 °C). Their presence does not explain the inhibiting effect of CO₂ observed in CCM on Pd/γ-Al₂O₃ catalysts.     

聚合工艺条件对含氟涂膜表面性能的影响

运用种子乳液聚合法制备了较高性价比的含氟乳液。FTIR光谱和DSC测试表明,含氟单体参与了聚合反应。运用KrussK12型动态表面能分析仪,测定聚合工艺中以不同用量的乳化剂、引发剂、含氟单体、N 羟甲基丙烯酰胺(N MA)在不同的单体滴加速度下合成的乳液涂膜对水和十六烷的接触角,结果表明,w(乳化剂)=3 5%、w(引发剂)=0 45%、w(N MA)=4%、聚合物中x(F)=14%时,乳液涂膜对水和十六烷的接触角较佳,对水的接触角达115°,涂膜表现出良好的表面性能。     

Effects of deposition temperature on the crystallinity of Ba0.5Sr0.5TiO3 epitaxial thin films integrated on Si substrates by pulsed laser deposition method

Epitaxial Ba_0.5Sr_0.5TiO₃ (BSTO) thin films were grown on TiN buffered Si (0 0 1) substrates by PLD method and the effects of deposition temperature on their crystallinity and microstructure were studied. BSTO thin films were prepared with substrate temperature ranging from 350 to 650 °C. The BSTO films grown at below 400 °C showed amorphous phase and the film grown at 450 °C showed mixed phase of crystalline and amorphous, where crystalline phase was observed only at the top surface portion of the film. The BSTO films with fully crystalline phase were obtained in the samples deposited at above 500 °C. The (0 0 l) preferred orientation and the crystallinity of the BSTO films were improved with increasing the temperature. The dielectric constant, measured at 100 kHz and at room temperature, of the BSTO film grown at 650 °C was measured to be as high as 1129.     

Adhesive and repulsive properties of water droplet impact on honeycomb surfaces through breath figure method

The honeycomb porous films of tadpole‐shaped polyhedral oligomeric silsesquioxane fluorinated acrylates copolymers were fabricated through breath figure method. The static hydrophobic properties were studied through water contact angles (CAs) and the rim width/pore size (W/D) values. It was found that the low W/D value and high fluorine content generally indicated a high water CA. The properties such as morphology variations, energy conversion, contact diameter, adhesive, and repulsive forces were investigated on the porous and pincushion films. Furthermore, the kinetic energy of the droplet was converted into surface energy and internal energy dissipation after it impacted the surface. The residual energy made the droplet to recoil and influenced the bouncing height. The contact diameter and bouncing height characterized the energy level of the surface, and determined the surface energies of the copolymer/water/air system as well as the wettability. Finally, the adhesion and repulsion of water droplet on different surface at the times of establish contact, maximum contact diameter, and maximum bouncing height were compared. This work was helpful for us to further understand and control the adhesive force and the repulsive force on the porous and pincushion structure films. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45476.     

Highly effective oxidative cracking of n-butane in light olefins on a novel cobalt catalyst

A Co-N on alumina catalyst yielded high performance in the oxidative cracking of n-butane to ethylene and propylene. A total of 47.7 wt.% yield of olefins including 31% of ethylene and 13% of propylene were obtained at 82% of n-butane conversion at 600 °C. Catalyst characterization by SEM, X-ray photoelectron spectroscopy (XPS), XRD and TPR studies suggested that a cobalt oxynitride phase was formed. This resulted in lowering the oxygen binding energy leading to enrichment in mobile, low energy, oxygen species that significantly accelerates the formation of lower olefins.     

Redox behavior of palladium at start-up in the Perovskite-type LaFePdOx automotive catalysts showing a self-regenerative function

In order to elucidate the superior start-up activity of LaFePdO_x catalysts in practical automotive emission control, the redox property of Pd species in a Perovskite-type LaFe_0.95Pd_0.05O₃ catalyst was studied at temperatures ranging from 100 to 400 °C using X-ray spectroscopic techniques. In a reductive atmosphere, and even at temperatures as low as 100 °C, Pd⁰ species is partially segregated out onto the catalyst surface from the B-site of the Perovskite-type matrix of LaFe_0.95Pd_0.05O₃. Passing through successive oxidizing atmospheres, the segregated Pd⁰ species is re-oxidized into Pd²⁺ at 200–300 °C. The formation of a solid solution between the re-oxidized Pd species and the Perovskite-type matrix begins to be seen at around 400 °C and accelerates at higher temperatures. Thus a quasi-reversible redox reaction between the surface Pd⁰ and the cationic Pd in the LaFe_0.95Pd_0.05O₃ matrix takes place. The start-up activity of LaFePd_xO_x catalysts can be attributed to Pd⁰ that segregates under the reductive atmosphere which is a natural part of the redox fluctuation in automotive exhaust gases at 100–200 °C.     

Preparation and properties of core–shell nanosilica/poly(methyl methacrylate–butyl acrylate–2,2,2‐trifluoroethyl methacrylate) latex

A core–shell nanosilica (nano‐SiO₂)/fluorinated acrylic copolymer latex, where nano‐SiO₂ served as the core and a copolymer of butyl acrylate, methyl methacrylate, and 2,2,2‐trifluoroethyl methacrylate (TFEMA) served as the shell, was synthesized in this study by seed emulsion polymerization. The compatibility between the core and shell was enhanced by the introduction of vinyl trimethoxysilane on the surface of nano‐SiO₂. The morphology and particle size of the nano‐SiO₂/poly(methyl methacrylate–butyl acrylate–2,2,2‐trifluoroethyl methacrylate) [P(MMA–BA–TFEMA)] core–shell latex were characterized by transmission electron microscopy. The properties and surface energy of films formed by the nano‐SiO₂/P(MMA–BA–TFEMA) latex were analyzed by Fourier transform infrared spectroscopy, differential scanning calorimetry, thermogravimetric analysis, scanning electron microscopy/energy‐dispersive X‐ray spectroscopy, and static contact angle measurement. The analyzed results indicate that the nano‐SiO₂/P(MMA–BA–TFEMA) latex presented uniform spherical core–shell particles about 45 nm in diameter. Favorable characteristics in the latex film and the lowest surface energy were obtained with 30 wt % TFEMA; this was due to the optimal migration of fluorine to the surface during film formation. The mechanical properties of the films were significantly improved by 1.0–1.5 wt % modified nano‐SiO₂. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Fluorinated a-C:H films investigated by thermal-induced gas effusion

Using thermal-induced gas effusion the decomposition of plasma deposited fluorinated a-C:H films has been investigated. The main contributions to the effusion spectra were found to come from hydrogen, hydrocarbons, CF₄ and HF. It is observed that hydrogen-related effusion is progressively substituted by the effusion of CF₄-related species as the fluorine content is increased, confirming that fluorine atoms substitute hydrogen in the amorphous network. At low fluorine contents (<10 at.%) the material is relatively compact and the effusion of hydrogen-related species (hydrogen molecules and hydrocarbons) dominate. For high enough fluorine concentrations a strong change in the effusion characteristics indicates that an interconnected network of voids is present. Strong effusion of CF₄-related species is found to be consistent with a surface desorption process and can be observed when CF_n bonds are present in the film microstructure and the void network dimensions are large enough, i.e. for films with the highest fluorine contents (∼20 at.%). The effusion results can be correlated to a structural transition from diamond-like to polymer-like film.     

Decomposition of NO over Cu-AITS-1 zeolites

H-AITS-1 zeolite with Si/Ti = 50 and Si/Al = 50 was employed in preparing catalyst samples by ion-exchange and impregnation with a copper nitrate solution to obtain 0.24–1.15 wt.% and 1.5, 2 and 2.5 wt.% Cu loading, respectively. The catalytic properties for the NO decomposition were compared with that of Cu-ZSM-5 (Si/Al = 25 with 2 wt.% Cu loading) and similarity was found between the AITS-1 based samples and Cu-ZSM-5. Due to the higher acidity, the activity at 500°C per total copper atoms (an apparent turnover frequency, TOF) was significantly higher over Cu based AITS-1 samples being 2–3 × 10⁻³ s⁻¹ as compared to 1 × 10⁻³ s⁻¹ measured on Cu-ZSM-5. For the ion-exchanged Cu-AITS-1 there was an increase in TOF with increasing copper content, whereas on the impregnated samples a decrease in TOF was found. On all catalysts there was a maximum in the NO conversion at 500–550°C. The amount of NO per copper atom measured by temperature programmed desorption (TPD) was about the same as that on Cu-ZSM-5 and the features of the TPD were also similar. At the first contact of the catalyst at 500°C with the 2 vol% NO/Ar gas a transient N₂O formation and a considerable delay in the O₂ formation was observed. This could, however, be reproduced only on fresh catalyst, while all further transients showed different but reproducible features using the same sample.     

Reactor and in situ FTIR studies of Pt/BaO/Al2O3 and Pd/BaO/Al2O3 NOx storage and reduction (NSR) catalysts

The reduction of NO under cyclic “lean”/“rich” conditions was examined over two model 1 wt.% Pt/20 wt.% BaO/Al₂O₃ and 1 wt.% Pd/20 wt.% BaO/Al₂O₃ NO_x storage reduction (NSR) catalysts. At temperatures between 250 and 350 °C, the Pd/BaO/Al₂O₃ catalyst exhibits higher overall NO_x reduction activity. Limited amounts of N₂O were formed over both catalysts. Identical cyclic studies conducted with non-BaO-containing 1 wt.% Pt/Al₂O₃ and Pd/Al₂O₃ catalysts demonstrate that under these conditions Pd exhibits a higher activity for the oxidation of both propylene and NO. Furthermore, in situ FTIR studies conducted under identical conditions suggest the formation of higher amounts of surface nitrite species on Pd/BaO/Al₂O₃. The IR results indicate that this species is substantially more active towards reaction with propylene. Moreover, its formation and reduction appear to represent the main pathway for the storage and reduction of NO under the conditions examined. Consequently, the higher activity of Pd can be attributed to its higher oxidation activity, leading both to a higher storage capacity (i.e., higher concentration of surface nitrites under “lean” conditions) and a higher reduction activity (i.e., higher concentration of partially oxidized active propylene species under “rich” conditions). The performance of Pt and Pd is nearly identical at temperatures above 375 °C.     

Fluorinated polyacrylates containing amino side chains for the surface modification of waterborne epoxy resin

Fluorinated polyacrylates containing amino side chains (FACAs) were synthesized to improve the water repellency of waterborne epoxy resin. First, FACA was prepared by a two-step process. Then, a phase-inversion emulsion technique, taking FACA as the reactive surface additives, was employed to prepare waterborne epoxy resin. The effect of the fluorinated content and the length of the fluorine side chain on the surface, thermal, and bulk properties of the waterborne epoxy resin were investigated. It was observed that moderate increase of the fluorinated content or the length of the fluorine side chain improved the contact angle and thermal properties while the mechanical property was not deteriorated. A small amount of fluoride (0.07 wt %) in the EA-F1/3-1 sample can dramatically increase the water contact angle from 72.63° to 95.31° due to the strong tendency of the macromonomers to migrate toward the outmost layer, resulting in enrichment of fluorine atoms on the surface. X-ray photoelectron spectroscopy results revealed that for a given weight of the two macromonomers, F atomic concentration of the copolymer modified by longer fluorinated side chains was higher than that modified by short fluorinated side chains. From the present investigation, FACA successfully improved the surface property of waterborne epoxy resin and showed a prominent potential application in large-scale industrialization. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47091.     

Simultaneous production of hydrogen and carbon nanostructures by decomposition of propane and cyclohexane over alumina supported binary catalysts

Nano-scale, binary, 4.5 wt.% Fe–0.5 wt.% M (M = Pd, Mo or Ni) catalysts supported on alumina have been shown to be very effective for the decomposition of lower alkanes to produce hydrogen and carbon nanofibers or nanotubes. After pre-reduction at 700 °C, all three binary catalysts exhibited significantly lower propane decomposition temperatures and longer time-on-stream performances than either the non-metallic alumina support or 5 wt.% Fe/Al₂O₃. Catalytic decomposition of propane using all three catalysts yielded only hydrogen, methane, unreacted propane, and carbon nanotubes. Above 475 °C, hydrogen and methane were the only gaseous products. Catalytic decomposition of cyclohexane using the (4.5 wt.% Fe–0.5 wt.% Pd)/Al₂O₃ catalyst produced primarily hydrogen, benzene, and unreacted cyclohexane below 450 °C, but only hydrogen, methane, and carbon nanotubes above 500 °C. The carbon nanotubes exhibited two distinct forms depending on the reaction temperature. Above 600 °C, they were predominantly in form of multi-walled nanotubes with parallel walls in the form of concentric graphene sheets. At or below 500 °C, carbon nanofibers with capped and truncated stacked-cone structure were produced. At 625 °C, decomposition of cyclohexane produced a mixture of the two types of carbon nanostructures.     

Low-temperature complete oxidation of BTX on Pt/activated carbon catalysts

The catalytic destruction of volatile organic compound (VOC) benefits from a low oxidation temperature due to less energy consumption. In this study, activated carbon-supported Pt catalysts were prepared for benzene, toluene and xylene (BTX) deep oxidation at below 200°C. Activated carbon can serve as a media for concentrating VOC. The carbon supports were heated to 400 or 800°C under N₂ flow and washed with HF acid to remove surface impurities and/or minerals. The 0.3 wt.% Pt/activated carbon catalysts were prepared by the incipient wetness method, followed by H₂ reduction at 300°C for 2 h. The catalytic oxidation was conducted with a BTX concentration ranging from 640 to 2000 ppmv in air at volume hour space velocity (VHSV) of approximately 21 000 h⁻¹. The light-off curves were very steep and the light-off temperatures ranged between 130 and 150°C, well below those of the Pt/Al₂O₃ catalyst. The oxidation activity was promoted because of a higher surface BTX concentration due to the adsorption capability of activated carbons. Moisture reduces the activity only slightly due to the hydrophobicity of activated carbon. Generally, the Pt catalysts with thermally-treated activated carbon had lower ignition temperatures. Experimental results indicated that high-temperature pretreatment of activated carbon could effectively increase the catalyst activity. Meanwhile, X-ray photoelectron spectroscopy (XPS)/secondary ion mass spectroscopy (SIMS) investigation revealed that the graphitized surface might play a role in catalytic activity. Finally, this work suggested a reaction mechanism based on the adsorption-migration of hydrocarbons to reveal the enhanced activity of activated carbon support.