Fluorinated Ethylene Propylene Teflon Research Articles

Energy harvester using piezoelectric nanogenerator and electrostatic generator

This study demonstrates an energy harvester that combines a piezoelectric nanogenerator and an electret-based electrostatic generator. The device consists of an in-house fabricated nanocomposite (polydimethylsiloxane/barium titanate/carbon nanotube) as a piezoelectric layer and a monocharged Teflon fluorinated ethylene propylene as an electret electrostatic layer. The mechanical impedance of the structure can be altered easily by changing the nanocomposite monomer/cross-linker ratio and optimizing various mechanical energy sources. The energy harvester's performance was characterized by performing measurements with different frequencies (5–20 Hz) under applied dynamic loading. A total volumetric power density of ∼8.8 μW cm−3 and a total stored energy of ∼50.2 μJ min−1 were obtained. These findings indicate that this versatile, lightweight, and low-cost energy harvester can be employed as a power supply source for microelectronics in applications, such as wearables.

Transparent, Hydrophobic Fluorinated Ethylene Propylene Offers Rapid, Robust, and Irreversible Passive Adsorption of Diagnostic Antibodies for Sensitive Optical Biosensing.

Current literature data is scarce and somehow contradictory in respect to the suitability of "nonstick" fluoropolymer surfaces for immobilization of biomolecules. We have previously shown empirically that transparent Teflon fluorinated ethylene propylene (FEP) offers rapid and sensitive optical biosensing of clinically relevant biomarkers. This study shows for the first time a comprehensive experimental analysis of passive adsorption of diagnostic IgG antibodies on actual Teflon FEP microfluidic strips. Full equilibrium isotherms and kinetics for passive adsorption were studied and modeled employing a protein titration method using hundreds of multibore microfluidic strips for a range of temperatures, pH, ionic strengths, and inner diameters, using both polyclonal and monoclonal antibody systems. Results were benchmarked against other plastic hydrophobic and glass hydrophilic capillary surfaces. For the first time, it was shown quantitatively that the hydrophobicity of fluoropolymer surfaces encourages the passive adsorption of diagnostic antibodies for biosensing and is insensitive to the temperature of incubation and to ionic buffer strength. The mass of captured antigen increased with increasing antibody surface coverage up to ∼400 ng/cm2, with an optimal adsorbed antibody activity for 45-69% of full monolayer coverage, matching results of other biosensing surfaces. The equilibrium was reached fast, within 5-10 min, and surprisingly both the kinetics and equilibrium of antibody adsorption were dependent on the inner diameter of microcapillaries. This is a novel and relevant result that will generally impact on the design of miniaturized microfluidic biosensing devices. The antibody surface densities obtained with hydrophobic plastic surfaces were 2- to 4-fold lower than for a hydrophilic, glass surface, however the former presented a monolayered adsorption with a higher level of irreversibility, as shown by the adsorption and desorption rates around 1 order of magnitude smaller than for glass, which is highly desirable for biosensing with surface-coated biomolecules.

Continuous Recirculation of Microdroplets in a Closed Loop Tailored for Screening of Bacteria Cultures.

Emerging microfluidic technology has introduced new precision controls over reaction conditions. Owing to the small amount of reagents, microfluidics significantly lowers the cost of carrying a single reaction. Moreover, in two-phase systems, each part of a dispersed fluid can be treated as an independent chemical reactor with a volume from femtoliters to microliters, increasing the throughput. In this work, we propose a microfluidic device that provides continuous recirculation of droplets in a closed loop, maintaining low consumption of oil phase, no cross-contamination, stabilized temperature, a constant condition of gas exchange, dynamic feedback control on droplet volume, and a real-time optical characterization of bacterial growth in a droplet. The channels (tubing) and junction cubes are made of Teflon fluorinated ethylene propylene (FEP) to ensure non-wetting conditions and to prevent the formation of biofilm, which is particularly crucial for biological experiments. We show the design and operation of a novel microfluidic loop with the circular motion of microdroplet reactors monitored with optical sensors and precision temperature controls. We have employed the proposed system for long term monitoring of bacterial growth during the antibiotic chloramphenicol treatment. The proposed system can find applications in a broad field of biomedical diagnostics and therapy.

Simulated Low-Earth-Orbital Exposure of Thermal Control Materials

A variety of common spacecraft thermal control materials were exposed to a laboratory test designed to simulate the effects of the low-Earth-orbital space-radiation environment. The goal of this test program was to garner performance data on the subject materials, which included two thickness types of old and new rear-surface-silverized fluorinated ethylene propylene Teflon® tape manufactured more than a decade apart, an embossed version of rear-surface-silverized fluorinated ethylene propylene Teflon tape, perforated rear-surface-aluminized Kapton, and a zinc oxide/methyl silicone white paint. In addition to providing high-fidelity data on the end-of-life performance of the materials, the testing revealed that older samples of the rear-surface-silverized fluorinated ethylene propylene Teflon tape showed widely disparate responses and greater solar absorptance increases compared to samples of the same, newly manufactured materials. Samples of the new rear-surface-silverized fluorinated ethylene propylene Teflon tape and the other tested materials all performed commensurately, ruling out exposure inhomogeneity as the cause of the disparate behavior of the older rear-surface-silverized fluorinated ethylene propylene Teflon samples. Two older samples of the rear-surface-silverized fluorinated ethylene propylene Teflon tape also showed mottling and discoloration not exhibited by the newer tape materials. Microscopic examination of the rear-surface-silverized fluorinated ethylene propylene Teflon tapes revealed the presence of cracks in their metal coatings, confirming the root cause of the mottling to be adhesive bleeding through the cracks.

Radiation Induced Conductivity in Teflon FEP Irradiated With Multienergetic Electron Beam

Teflon Fluorinated Ethylene Propylene (FEP), used as thermal blankets on satellites, has a specific electrical behavior under space ionizing environment. Charging behaviors of this dielectric material, under electron beam irradiation, is of special interest for future spacecraft needs. Hence, ground experimental parameters have been adjusted in order to distinguish between the different physical mechanisms that steers FEP charging potential. The effect of incident electron spectrum, electric field, and dose rate has been investigated through surface potential measurements during and after the irradiation process. The experimental results especially reveal that charging potential evolution as a function of time is not strongly dependent upon the electron spectrum and the electric field but varies noticeably with dose rate. These results have been analyzed in the light of a physical model that takes into account ionization, trapping/detrapping, and recombination mechanisms for negative and positive charges.

Gaseous elemental mercury (GEM) emissions from snow surfaces in northern New York.

Snow surface-to-air exchange of gaseous elemental mercury (GEM) was measured using a modified Teflon fluorinated ethylene propylene (FEP) dynamic flux chamber (DFC) in a remote, open site in Potsdam, New York. Sampling was conducted during the winter months of 2011. The inlet and outlet of the DFC were coupled with a Tekran Model 2537A mercury (Hg) vapor analyzer using a Tekran Model 1110 two port synchronized sampler. The surface GEM flux ranged from −4.47 ng m−2 hr−1 to 9.89 ng m−2 hr−1. For most sample periods, daytime GEM flux was strongly correlated with solar radiation. The average nighttime GEM flux was slightly negative and was not well correlated with any of the measured meteorological variables. Preliminary, empirical models were developed to estimate GEM emissions from snow surfaces in northern New York. These models suggest that most, if not all, of the Hg deposited with and to snow is reemitted to the atmosphere.

Monte Carlo simulations and radiation dosimetry measurements of 142Pr capillary tube-based radioactive implant (CTRI): a new structure for brachytherapy sources

Previously, a promising β(-)-emitting praseodymium-142 glass seed was proposed for brachytherapy of prostate cancer. In accordance with the previous study, a (142)Pr capillary tube-based radioactive implant (CTRI) was suggested as a source with a new structure to enhance application of β(-)-emitting radioisotopes such as (142)Pr in brachytherapy. Praseodymium oxide powder was encapsulated in a glass capillary tube. Then, a thin and flexible fluorinated ethylene propylene Teflon(®) layer sealed the capillary tube. The source was activated in the Tehran Research Reactor by the (141)Pr(n,γ) (142)Pr reaction. Measurements of the dosimetric parameters were performed using GafChromic(®) radiochromic film. In addition, the dose rate distribution of (142)Pr CTRI was calculated by modeling (142)Pr source in a water phantom using Monte Carlo N-Particle Transport (MCNP5) Code. The active source was unreactive and did not leak in water. In comparison with the earlier proposed (142)Pr seed, the suggested source showed similar desirable dosimetric characteristics. Moreover, the (142)Pr CTRI production procedure may be technically and economically more feasible. The mass of praseodymium in CTRI structure could be greater than that of the (142)Pr glass seed; therefore, the required irradiation time and the neutron flux could be reduced. A (142)Pr CTRI was proposed for brachytherapy of prostate cancer. The dosimetric calculations by the experimental measurements and Monte Carlo simulation were performed to fulfill the requirements according to the American Association of Physicists in Medicine recommendations before the clinical use of new brachytherapy sources. The characteristics of the suggested source were compared with those of the previously proposed (142)Pr glass seed.

Alucone Interlayers to Minimize Stress Caused by Thermal Expansion Mismatch between Al2O3 Films and Teflon Substrates

Alucone films were employed as interlayers to minimize stress caused by thermal expansion mismatch between Al(2)O(3) films grown by atomic layer deposition (ALD) and Teflon fluorinated ethylene propylene (FEP) substrates. The alucone films were grown by molecular layer deposition (MLD) using trimethylaluminum (TMA), ethylene glycol (EG), and H(2)O. Without the alucone interlayer, the Al(2)O(3) films were susceptible to cracking resulting from the high coefficient of thermal expansion (CTE) mismatch between the Al(2)O(3) film and the Teflon FEP substrate. Cracking was observed by field emission scanning electron microscopy (FE-SEM) images of Al(2)O(3) films grown directly on Teflon FEP substrates at temperatures from 100 to 160 °C and then cooled to room temperature. With an alucone interlayer, the Al(2)O(3) film had a crack density that was reduced progressively versus alucone interlayer thickness. For Al(2)O(3) film thicknesses of 48 nm deposited at 135 °C, no cracks were observed for alucone interlayer thicknesses >60 nm on 50 μm thick Teflon FEP substrates. For thinner Al(2)O(3) film thicknesses of 21 nm deposited at 135 °C, no cracks were observed for alucone interlayer thicknesses >40 nm on 50 μm thick Teflon FEP substrates. Slightly higher alucone interlayer thicknesses were required to prevent cracking on thicker Teflon FEP substrates with a thickness of 125 μm. The alucone interlayer linearly reduced the compressive stress on the Al(2)O(3) film caused by the thermal expansion mismatch between the Al(2)O(3) coating and the Teflon FEP substrate. The average compressive stress reduction per thickness of the alucone interlayer was determined to be 8.5 ± 2.3 MPa/nm. Comparison of critical tensile strains for alucone films on Teflon FEP and HSPEN substrates revealed that residual compressive stress in the alucone film on Teflon FEP could help offset applied tensile stress and lead to the attainment of much higher critical tensile strains.

Critical tensile and compressive strains for cracking of Al2O3 films grown by atomic layer deposition

Al2O3 atomic layer deposition (ALD) is a model ALD system and Al2O3 ALD films are excellent gas diffusion barrier on polymers. However, little is known about the response of Al2O3 ALD films to strain and the potential film cracking that would restrict the utility of gas diffusion barrier films. To understand the mechanical limitations of Al2O3 ALD films, the critical strains at which the Al2O3 ALD films will crack were determined for both tensile and compressive strains. The tensile strain measurements were obtained using a fluorescent tagging technique to image the cracks. The results showed that the critical tensile strain is higher for thinner thicknesses of the Al2O3 ALD film on heat-stabilized polyethylene naphthalate (HSPEN) substrates. A low critical tensile strain of 0.52% was measured for a film thickness of 80 nm. The critical tensile strain increased to 2.4% at a film thickness of 5 nm. In accordance with fracture mechanics modeling, the critical tensile strains and the saturation crack densities scaled as (1/h)1/2 where h is the Al2O3 ALD film thickness. The fracture toughness for cracking, KIC, of the Al2O3 ALD film was also determined to be KIC = 2.30 MPa m1/2. Thinner Al2O3 ALD film thicknesses also had higher critical strains for cracking from compressive strains. Field-emission scanning electron microscopy (FE-SEM) images revealed that Al2O3 ALD films with thicknesses of 30–50 nm on Teflon fluorinated ethylene propylene (FEP) substrates cracked at a critical compressive strain of ∼1.0%. The critical compressive strain increased to ∼2.0% at a film thickness of ∼20 nm. A comparison of the critical tensile strains on HSPEN substrates and critical compressive strains on Teflon FEP substrates revealed some similarities. The critical strain was ∼1.0% for film thicknesses of 30–50 nm for both tensile and compressive strains. The critical compressive strain then increased more rapidly than the critical tensile strain for thinner films with thicknesses < 30 nm. The high critical tensile and compressive strains for thin Al2O3 ALD films should be very useful for flexible gas diffusion barriers on polymers.

Teflon films for chemically-inert microfluidic valves and pumps

We present a simple method for fabricating chemically-inert Teflon microfluidic valves and pumps in glass microfluidic devices. These structures are modeled after monolithic membrane valves and pumps that utilize a featureless polydimethylsiloxane (PDMS) membrane bonded between two etched glass wafers. The limited chemical compatibility of PDMS has necessitated research into alternative materials for microfluidic devices. Previous work has shown that spin-coated amorphous fluoropolymers and Teflon-fluoropolymer laminates can be fabricated and substituted for PDMS in monolithic membrane valves and pumps for space flight applications. However, the complex process for fabricating these spin-coated Teflon films and laminates may preclude their use in many research and manufacturing contexts. As an alternative, we show that commercially-available fluorinated ethylene-propylene (FEP) Teflon films can be used to fabricate chemically-inert monolithic membrane valves and pumps in glass microfluidic devices. The FEP Teflon valves and pumps presented here are simple to fabricate, function similarly to their PDMS counterparts, maintain their performance over extended use, and are resistant to virtually all chemicals. These structures should facilitate lab-on-a-chip research involving a vast array of chemistries that are incompatible with native PDMS microfluidic devices.

Sensitive profiling of chemically diverse bioactive lipids

Here, we present an improved method for sensitive profiling of lipids in a single high-performance liquid chromatography-electrospray ionization-quadrupole time of flight mass spectrometry experiment. The approach consists of i) sensitive isocratic elution, which takes advantage of C18 column material that is resistant to increased pH values induced by piperidine, ii) chemometric alignment of mass spectra followed by differential analysis of ion intensities, and iii) semiquantitative analysis of extracted ion chromatograms of interest. A key advantage of this method is its wide applicability to extracts that harbor lipids of considerable chemical complexity. The method allows qualitative and semiquantitative analysis of fatty acyls, glycerophospholipids (such as glycerophosphatidylinositols, glycerophosphatidylserines, and glycerophosphatidylcholines in brain extracts), phosphatidylinositol mannosides, acylated glycerophospholipids, sphingolipids (including ceramides and gangliosides in brain extracts), and, for the first time with ESI, prenols and mycolic acids (MAs). MAs are targets in antimycobacterial therapy, and they play an important immunomodulatory role during host-pathogen interactions. We compared high-resolution mass spectra of MAs derived from Mycobacterium bovis Bacille Camette-Guérin during entry into nonreplicative conditions induced by oxygen deprivation (hypoxic dormancy). Although the overall composition is not drastically altered, there are pronounced differences in individual MAs. alpha-MAs accumulate during entry into dormancy, whereas a subpopulation of keto-MAs is almost entirely eliminated. This effect is reversed upon resuscitation of dormant mycobacteria. These results provide detailed chemical information with relevance to drug development and immunobiology of mycobacteria.

Efects of Micuum Ultraviolet Radiation of Irious Wavelength Ranges on Teflon® FEP Film

This paper describes testing to investigate the effects of vacuum ultraviolet (VUV) radiation on Teflon fluorinated ethylene propylene (FEP) film, examining differences in mechanical properties degradation for samples of 50.8 jtm thickness exposed to VUV of various lower cut-off wavelengths. Samples were illuminated in a high vacuum facility by deuterium lamps, which provide radiation in the 115-400 nm wavelength range, but with the highest intensity being below 200 nm. Windows of fused silica, crystalline quartz, and magnesium fluoride provided lower cut-off wavelengths of 155, 140 and 115 nm, respectively. Lamp intensity was measured in the 115-200 nm wavelength range throughout the sample exposures. The determined intensities were used to estimate intensity and incident energy of various wavelength ranges, between 115 and 400 nm. Samples were analysed for tensile strength and elongation at failure. The effects of radiation exposures of different wavelength ranges were compared and discussed in terms of the expected depth to which radiation of various wavelengths is deposited into FEP

Thermal Contributions to the Degradation of Ground Laboratory and Space-Irradiated Teflon

The aluminized Teflon fluorinated ethylene propylene outer most layer of the multilayer insulation blankets on the Hubble Space Telescope has become embrittled resulting in severe on-orbit cracking. During the second servicing mission, a piece of aluminized fluorinated ethylene propylene was retrieved that had curled, exposing the back-surface aluminum to space. This extremely embrittled piece reached 200 C on-orbit, 150 C higher than the nominal temperature extreme. Therefore, experiments have been conducted to determine the effect of heating on the degradation of fluorinated ethylene propylene that has been irradiated in a ground laboratory facility or in space on Hubble Space Telescope. Samples of pristine, x-ray irradiated and Hubble Space Telescope retrieved fluorinated ethylene propylene were heat treated from 50 to 200 C at 25 C intervals in a high vacuum facility and tensile tested. Density measurements were also obtained. Results indicate that heating does not embrittle non-irradiated Teflon. However, there is a significant dependence of the embrittlement of irradiated Teflon on heating temperature, with near complete loss of elongation at 100 C and higher. Rate of degradation changes, which were consistent with the glass transition temperature for fluorinated ethylene propylene, were present in the data. The results support chain scission as the primary mechanism of degradation of fluorinated ethylene propylene on Hubble Space Telescope, and indicate the significance of the on-orbit temperature of fluorinated ethylene propylene with respect to its degradation in the space environment.

Electron-beam-induced discharge phenomena of teflon films for space use

We investigated the discharge phenomena of Teflon FEP (fluorinated ethylene propylene) films used as thermal control material of spacecraft by electron-beam irradiation simulating hot plasma in space. FEP films of two thicknesses, 25 and 127 μm, were tested. The results obtained were as follows. (1) In 127-μm-thick FEP film, a surface discharge triggered by high electric field at the triple junction of the edge of the metal frame occurred. (2) In 25-μm-thick FEP film, punchthrough discharge accompanied by surface flashover occurred. (3) Discharge frequency increased as nearly the 1/2 power of the electron-beam current density under constant irradiation energy. On the other hand, it increased linearly with the irradiation energy under constant beam current density, but with sufficient threshold electron energy to cause discharge. These results were explained by comparison between the surface electric field and the bulk electric field in FEP film obtained analytically by using a two-dimensional charging model. © 1999 Scripta Technica, Electr Eng Jpn, 129(1): 10–19, 1999

Evaluation of granulated BGO, GSO:Ce, YAG:Ce, CaF 2:Eu and ZnS:Ag for alpha/beta pulse shape discrimination in a flow-cell radiation detector

Granulated BGO, GSO:Ce, YAG:Ce, and CaF 2:Eu; CaF 2:Eu coated with a fluorescent polymer, and combinations of coated and uncoated CaF 2:Eu with ZnS:Ag were evaluated for their ability to discriminate between alpha and beta particles in a flow-cell radiation detector. The evaluations were based on the analysis of pulse shape spectra. Various granulated scintillators were packed into flow cell detectors that were coils of 3.0 mm OD×1.5 mm ID fluorinated ethylene propylene Teflon ® tubing positioned between dual photomultiplier tubes for analysis. The best pulse shape discrimination was obtained for a combination of equal masses of uncoated CaF 2:Eu (63–90 μm) and ZnS:Ag (10 μm), which had a 9% spillover. Additional research is needed to reduce the spillover.

Potential calibration errors in carbonyl sulfide permeation devices: Implications for atmospheric studies

Ambient in situ measurements of the important sulfur gas carbonyl sulfide (OCS) very frequently rely on permeation devices based on weight loss measurements (gravimetry) as the method of calibration. Both time series studies as well as measurements of OCS sources and sinks typically employ this approach. Although this calibration approach is based upon fundamental quantities, its accuracy directly depends upon the purity of the permeating effluent. The present study describes a systematic investigation of four permeation wafers and their time history based on gravimetry, direct absorption spectroscopy employing a tunable diode laser absorption spectrometer (TDLAS), and two different ratio approaches. Gravimetric determinations for two of the devices, which employed fluorinated ethylene propylene (FEP) Teflon wafers as the permeating medium, indicated mass loss rates which decayed exponentially with time. This is in contrast to the direct absorption and ratio measurements, which were significantly lower at the start (37% in one case and 19% in the other) and displayed a small linear drop with time. We present evidence for the presence of a CO2 impurity in FEP permeation devices, either from the starting material or the breakdown of OCS. This impurity copermeates along with OCS but at a much faster rate, giving rise to an apparent exponential decay in the OCS rate. Calculations based on fundamental permeability parameters for CO2 in FEP Teflon and typical levels of CO2 impurity (0.1 to 2%) in the starting material yield results that are consistent with the present interpretation. Two other permeation wafers, which employed polytetrafluoroethylene (PTFE) Teflon membranes, exhibited completely different behavior; all the measurement methods indicated similar results and showed a linearly decreasing permeation rate with time. The CO2 impurity problem prevalent in FEP wafers is insignificant in PTFE wafers because the permeability of PTFE is at least 21 times higher. It is possible that the high pressure inside the membrane (POCS = 17.7 atm at 40°C) alters the crystalline PTFE structure with time, resulting in a real decrease in permeation rate. Although more studies are needed to further confirm and extend these findings, the effects observed here suggest that ambient OCS measurements could in some circumstances be systematically high by as much as 37%. Such errors can produce erroneous temporal trends and/or inconsistencies between ambient measurements carried out by different laboratories.

Culture materials affect ex vivo expansion of hematopoietic progenitor cells.

Ex vivo expansion of hematopoietic cells is important for applications such as cancer treatment, gene therapy, and transfusion medicine. While cell culture systems are widely used to evaluate the biocompatibility of materials for implantation, the ability of materials to support proliferation of primary human cells in cultures for reinfusion into patients has not been addressed. We screened a variety of commercially available polymer (15 types), metal (four types), and glass substrates for their ability to support expansion of hematopoietic cells when cultured under conditions that would be encountered in a clinical setting. Cultures of peripheral blood (PB) CD34+ cells and mononuclear cells (MNC) were evaluated for expansion of total cells and colony-forming unit-granulocyte monocyte (CFU-GM; progenitors committed to the granulocyte and/or monocyte lineage). Human hematopoietic cultures in serum-free medium were found to be extremely sensitive to the substrate material. The only materials tested that supported expansion at or near the levels of polystyrene were tissue culture polystyrene, Teflon perfluoroalkoxy, Teflon fluorinated ethylene propylene, cellulose acetate, titanium, new polycarbonate, and new polymethylpentene. MNC were less sensitive to the substrate materials than the primitive CD34+ progenitors, although similar trends were seen for expansion of the two cell populations on the substrates tested. CFU-GM expansion was more sensitive to substrate materials than was total cell expansion. The detrimental effects of a number of the materials on hematopoietic cultures appear to be caused by protein adsorption and/or leaching of toxins. Factors such as cleaning, sterilization, and reuse significantly affected the performance of some materials as culture substrates. We also used PB CD34+ cell cultures to examine the biocompatibility of gas-permeable cell culture and blood storage bags and several types of tubing commonly used with biomedical equipment. While many of the culture bag materials gave satisfactory results, all of the tubing materials severely inhibited total cell and CFU-GM expansion. Taken together, our results show that many materials approved for blood contact or considered biocompatible are not suitable for use with hematopoietic cells cultured in serum-free medium. As hematopoietic cultures are scaled up for a variety of clinical applications, it will be essential to carefully examine the biocompatibility of all materials involved.

Preparation and characterization of teflon–FEP films grafted with acrylic acid by radiochemical method

AbstractIn an attempt to prepare permselective membrane, grafting of acrylic acid (AAc) onto Teflon–fluorinated ethylene‐propylene (FEP) film was studied in aqueous medium by the preirradiation method in air. Grafting was carried out by heating a mixture of AAc, water, and preirradiated Teflon–FEP film in air at 93°C for definite time periods. Percentage ofgrafting was determined as a function of total dose, monomer concentration, reaction time, and amount of water. Maximum percentage of grafting (60.17%) was obtained at a total dose of 4.8 Mrad using 0.07M [AAc]. Evidence of grafting was obtained from the physical appearance and swelling behavior of the grafted film in polar solvents. Infrared spectroscopic and thermal analysis of the grafted film provided additional evidence for grafting. A plausible mechanism for grafting of AAc onto preirradiated Teflon–FEP film in air has been proposed. © 1995 John Wiley & Sons, Inc.

Measurements of dimethyl sulfide and H2S over the western North Atlantic and the tropical Atlantic

Airborne measurements of DMS and H2S were made off the east coast of the United States and over the tropical Atlantic off Brazil. Samples were collected through a fluorinated ethylene propylene Teflon inlet manifold. Dimethyl sulfide (DMS) was preconcentrated onto gold wool and analyzed by gas chromatography/flame photometric detection. H2S was collected on AgNO3‐impregnated filters and determined by fluorescence quenching. Use of a new scrubber material (cotton) to remove negative interference on DMS measurements was investigated. Comparison with a Na2CO3/Anakrom scrubber gave good overall agreement. Only under extreme conditions, e.g., on flight 9 (continental air mass, low humidity, high O3, and low DMS values) did Na2CO3 show noticeable loss of DMS compared to cotton. On most flights, especially in marine air masses with high humidity and relatively low O3, the results from both scrubbers agreed well with each other and with other instruments used during the intercalibration. Off the U.S. East Coast, DMS levels showed strong dependence on air mass origin with high values (up to 83 ppt) in marine tropical air masses and low values (10–20 ppt) in continental and polar air. Over the tropical Atlantic, DMS ranged over 20–100 ppt in the mixed layer. Nighttime values were a factor of 1.6–2.3 higher than daytime levels. DMS decreased with altitude to <1 ppt at 4000 m. H2S in the mixed layer off the U.S. East Coast ranged from 10 to 200 ppt. Significant influence from terrestrial and pollution sources was evident. H2S in air masses originating over the eastern seaboard was much higher than in continental polar air or over the remote tropical continents. In contrast, over the tropical Atlantic, concentrations were very low (5–10 ppt), typical of truly marine air. Night/day ratios were about 1.4. No significant geographical variability was seen in H2S levels over the tropical Atlantic. The correlation of atmospheric 222Rn and H2S was significant, with both being higher off the U.S. East Coast (H2S, 7–270 ppt; 222Rn, 2–20 pCi m−3) than over the tropical Atlantic (0.5‐10 ppt and 2–4 pCi m−3, respectively).

Update on the Vitek partial and total temporomandibular joint systems

A retrospective recall study was done on 262 VK I (N = 138) and VK II (N = 124) (Vitek, Inc, Houston, TX) partial and total temporomandibular joints placed between 1982 and 1990. The cumulative success rate of VK I total joints observed for up to 10 years was approximately 20%, whereas the success rate of VK II total joints observed up to 6 years was approximately 80%. At the 5- to 6-year interval for each, these rates were 44% and 79%, respectively. Wear of the Teflon fluorinated ethylene propylene polymer surface was the primary reason for VK I failure; there was no material failure of the VK II prostheses. Slightly better pain relief, increase in interincisal opening, improvement in diet, and greater overall satisfaction were noted with the use of VK II. A highly significant improvement in success data was found if no surgery had been performed before either VK I or VK II total joint placement. Rib grafts were not particularly helpful after removal of total joint prostheses, particularly if the patient had a history of multiple surgeries. Total temporomandibular joint surgery must be reserved for patients in whom alternative surgical methods have failed or are no longer indicated. All total joint implants, particularly the VK I, must be observed closely with clinical examination and imaging and removed at the earliest sign of material failure.