Fluorocarbon Membrane Research Articles

Preparation of normally open microvalves with fluorinated ethylene propylene membrane and poly(methyl methacrylate) substrates

Substitution of PDMS membrane with fluorocarbon membrane serving as the actuating elements has been reported in preparation of normally closed pneumatic valves, but rarely reported in fabrication of normally open valves. We presented a photoresist-free method to fabricate normally open valves using fluorinated ethylene propylene (FEP) film as the actuating membrane to close PMMA-based microfluidic channels. An arched FEP film top wall of compressed-gas-filled channel was used as the relief pattern to prepare a positive epoxy resin stamp, which was employed to hot-emboss the fluid channels with round cross section into PMMA substrates. An adhesive-assisted bonding technique was used to irreversibly bond the PMMA substrates to the FEP membrane. The chemical resistance, small molecule absorption and valve/pump properties of the fabricated pneumatic valves were characterized.

Polycyclic aromatic hydrocarbons (PAHs) in exhaust emissions from diesel engines powered by rapeseed oil methylester and heated non-esterified rapeseed oil

Polycyclic aromatic hydrocarbons (PAHs) of exhaust emissions were studied in four direct-injection turbocharged four-cylinder diesel engines, with power ratings of 90–136 kW. The engines were operated on biodiesel (B-100), a blend of 30% biodiesel in diesel fuel (B-30), and heated rapeseed oil (RO) in two independent laboratories. Diesel particle filters (DPF) and selective catalytic reduction (SCR) systems were used with B-30 and B-100. Concentrations of individual PAHs sampled in different substrates (quartz, borosilicate fiber and fluorocarbon membrane filters, polyurethane foam) were analyzed using different methods. Benzo[a]pyrene toxic equivalents (BaP TEQ) were calculated using different sets of toxic equivalency factors (TEF). Operation on B-100 without aftertreatment devices, compared to diesel fuel, yielded a mean reduction in PAHs of 73%, consistent across engines and among TEF used. A lower PAH reduction was obtained using B-30. The BaP TEQ reductions on DPF were 91–99% using B-100, for one non-catalyzed DPF, and over 99% in all other cases. The BaP TEQ for heated RO were higher than those for B-100 and one half lower to over twice as high as that of diesel fuel. B-100 and RO samples featured, compared to diesel fuel, a relatively high share of higher molecular weight PAH and a relatively low share of lighter PAHs. Using different sets of TEF or different detection methods did not consistently affect the observed effect of fuels on BaP TEQ. The compilation of multiple tests was helpful for discerning emerging patterns. The collection of milligrams of particulate matter per sample was generally needed for quantification of all individual PAHs.

Composite Fluorocarbon Membranes by Surface-Initiated Polymerization from Nanoporous Gold-Coated Alumina

This manuscript describes the versatile fabrication and characterization of a novel composite membrane that consists of a porous alumina support, a 100 nm thick nanoporous gold coating, and a selective poly(5-(perfluorohexyl)norbornene) (pNBF6) polymer that can be grown exclusively from the nanoporous gold or throughout the membrane. Integration of the three materials is achieved by means of silane and thiol chemistry, and the use of surface-initiated ring-opening metathesis polymerization (SI-ROMP) to grow the pNBF6. The use of SI-ROMP allows tailoring of the extent of polymerization of pNBF6 throughout the structure by varying polymerization time. Scanning electron microscopy (SEM) images indicate that the thin polymer films cover the structure entirely. Cross-sectional SEM images of the membrane not only corroborate growth of the pNBF6 polymer within both the porous alumina and the nanoporous gold coating but also show the growth of a pNBF6 layer between these porous substrates that lifts the nanoporous gold coating away from the alumina. Advancing contact angle (θ(A)) measurements show that the surfaces of these composite membranes exhibit both hydrophobic (θ(A) = 121-129)° and oleophobic (θ(A) = 69-74)° behavior due to the fluorocarbon side chains of the pNBF6 polymer that dominate the surface. Results from electrochemical impedance spectroscopy (EIS) confirm that the membranes provide effective barriers to aqueous ions, as evidenced by a resistive impedance on the order of 1 × 10(7) Ω cm(2). Sulfonation of the polymer backbone substantially enhances ion transport through the composite membrane, as indicated by a 40-60 fold reduction in resistive impedance. Ion transport and selectivity of the membrane change by regulating the polymerization time. The fluorinated nature of the sulfonated polymer renders the membrane selective toward molecules with similar chemical characteristics.

Influence of membrane surface properties on the growth of neuronal cells isolated from hippocampus

Membranes have become of great interest for tissue engineering application, since they offer the advantage of developing neuronal tissue that may be used in implantable or in vitro hybrid systems for the simulation of brain function. The behaviour of neurons isolated from the hippocampus on membranes with different surface properties was investigated. The different membranes used as substrates for cell adhesion consisted of polyester (PE), modified polyetheretherketone (PEEK-WC), fluorocarbon (FC) and polyethersulfone (PES), all of which coated with poly- l-lysine (PLL) in order to have the same functional groups interacting with cells. The membranes exhibited different morphological surface properties in terms of pore size, porosity and roughness. Hippocampal neurons exhibited a different morphology in response to varying the properties of the membrane surface. Indeed, cells grown on the smoother membranes and namely FC and PES membranes displayed a large number of neurites with consequent formation of bundles. As a consequence while a very complex network was formed on these membranes, cells tend to, instead, form aggregates and most of the processes are developed inside the pores of the membranes when rougher PEEK-WC surfaces were used. In addition, the secretion of brain-derived neurotrophic factor (BDNF) was expressed at high levels in neurons grown on FC membranes with respect to the other membranes. Taken together these results suggest the pivotal role played by membrane surface properties in the adhesion and growth of the hippocampal neurons, which must be considered in the development of tailored membranes for neural tissue engineering.

Key challenges and recent progress in batteries, fuel cells, and hydrogen storage for clean energy systems

Reducing or eliminating the dependency on petroleum of transportation systems is a major element of US energy research activities. Batteries are a key enabling technology for the development of clean, fuel-efficient vehicles and are key to making today's hybrid electric vehicles a success. Fuel cells are the key enabling technology for a future hydrogen economy and have the potential to revolutionize the way we power our nations, offering cleaner, more efficient alternatives to today's technology. Additionally fuel cells are significantly more energy efficient than combustion-based power generation technologies. Fuel cells are projected to have energy efficiency twice that of internal combustion engines. However before fuel cells can realize their potential, significant challenges remain. The two most important are cost and durability for both automotive and stationary applications. Recent electrocatalyst developments have shown that Pt alloy catalysts have increased activity and greater durability than Pt catalysts. The durability of conventional fluorocarbon membranes is improving, and hydrocarbon-based membranes have also shown promise of equaling the performance of fluorocarbon membranes at lower cost. Recent announcements have also provided indications that fuel cells can start from freezing conditions without significant deterioration. Hydrogen storage systems for vehicles are inadequate to meet customer driving range expectations (>300 miles or 500 km) without intrusion into vehicle cargo or passenger space. The United States Department of Energy has established three centers of Excellence for hydrogen storage materials development. The centers are focused on complex metal hydrides that can be regenerated onboard a vehicle, chemical hydrides that require off-board reprocessing, and carbon-based storage materials. Recent developments have shown progress toward the 2010 DOE targets. In addition DOE has established an independent storage material testing center to verify storage capacity of promising materials. These developments point to a viable path to achieving the DOE/FreedomCAR cost and performance goals. The transition to hydrogen-powered fuel cell vehicles will occur over the next 10–15 years. In the interim, fossil fuel consumption will be reduced by increased penetration of battery/gasoline hybrid cars.

Grafting and electrochemical characterisation of poly-(3,4-ethylenedioxythiophene) films, on Nafion and on radiation-grafted polystyrenesulfonate–polyvinylidene fluoride composite surfaces

The preparation and characterisation of poly-(3,4-ethylenedioxy)thiophene (PEDOT) films coated onto fluorocarbon membranes containing sulfonate groups, such as Nafion-117 and poly(styrene-4-sulfonate)-grafted poly(vinylidene fluoride) (PVDF-g-PSSA) membranes is described. The PEDOT layer is found to adhere very strongly on to both membranes, and is highly conductive. The organic polymer membranes can be used directly as working electrodes in electrochemical experiments, without any inert metal or semiconductor support. The composite materials are characterised by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS).

An Ultrathin Polymer Network through Polyion-Complex by Using Sodium Dioctadecyl Sulfate as Monolayer Template

Two-dimensionally cross-linked ultrathin films of poly(maleic acid-alt-methyl vinyl ether) (MA-MVE) and poly(allylamine) (PAA) were produced by using sodium dioctadecyl sulfate (2C18S) as the monolayer template for Langmuir-Blodgett (LB) depositio n. The template molecules were subsequently removed by thermal treatment followed by extraction. The polyion-complexed monolayers of three components, i.e., template 2C18S, co-spread PAA, and subphase MA-MVE, were formed at the air-water interface. Their monolayer properties were studied by the surface pressure-area isotherm. The monolayers were transferred on solid substrates as Y type. The polyion-complexed LB films and the resulting network films were characterized by FT-IR spectroscopy, X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM). The cross-linking to form a polymer network was achieved by amide or imide formation through heat treatment under a vacuum. SEM observation of the film on a porous fluorocarbon membrane filter (pore diameter 0.1 ㎛) showed covering of the pores by four layers in the polyion complex state. Extraction by chloroform followed by heat treatment produced hole defects in the film.

Polymeric Langmuir-Blodgett Films of Imidazole-Coordinated Metal Complexes

An imidazole-containing amphiphilic polymer (IMA-OVE) was synthesized and the metal-complexing capability of its monolayer at the air-water interface was examined. The polymer was obtained by radical copolymerization of N-(2-(4-imidazolyl)ethyl)maleamic acid (IMA) with n-octadecyl vinyl ether (OVE). Monolayers of IMA-OVE on aq. subphases containing metal ions were studied by measuring surface pressure-area isotherms. The preparation conditions of IMA-OVE Langmuir-Blodgett (LB) films on fluorocarbon membranes and calcium fluoride plates were studied and the physicochemical properties of the LB films were then examined by Raman, XPS, and FT-IR spectroscopy. The concentration of metal ions incorporated into the LB films was the order of Fe3+> Mg2+>Cu2+>K+.

Characteristics of organic gas sensitivity in copolymer LB films

The use of preformed copolymers and their cross-linking have been attempted in order to improve the intrinsic fragility of monolayers and Langmuir-Blodgett (LB) films and to make their technological applications possible. It has been shown that an imidization followed by a polyion-complexation can stabilize the LB films against heat and solvents. And, when the polymer structure was property designed, concurrent removal of the alkyl tails together with imide formation could he accomplished. In this paper, the interface can be transferred onto solid substrates such as porous fluorocarbon membranes filter and quartz crystal microbalance (QCM). The properties of the monolayers and the LB films investigated by π- A isotherms, FT-IR, DSC, deposition ratio, QCM and SEM will be discussed. In addition, it was attempted to investigate the reaction of polymer LB films in the organic gas surrounding by the use of QCM.

Membrane distillation with fluoro-carbon membranes

A partially hydrophilic fluoro-carbon composite membrane was tested for sea water desalination. The permeate flux increases with an increase in flow rate of brine and/or cooling water, as well as with an increase in temperature differences between brine and cooling water. The thermal efficiency also increases as the temperature difference increases. Comparison of the fluoro-carbon membrane with the silicone membrane revealed that the permeability and thermal efficiency of the fluoro-carbon membrane were superior to those of the silicone membrane.

Tangential flow filtration and preliminary phylogenetic analysis of marine picoplankton

A procedure was developed for harvesting gram quantities of microbial biomass from oligotrophic waters, when mixed populations are present in low abundance. Picoplankton from Atlantic Ocean (Hydrostation S, Sargasso Sea) and Pacific Ocean (Aloha Station) sites were collected in a three-stage process: (i) collection of seawater through an intake covered with 10-microns-pore Nytex; (ii) concentration by a tangential flow filtration device equipped with 10 ft2 (0.929 m2) of 0.1-micron-pore fluorocarbon membrane; (iii) collection of cells from concentrate by centrifugation. The overall efficiency of picoplankton recovery was at least 37%. The cellular morphotypes recovered matched those of the original population. DNA was prepared from frozen cell pellets by enzymatic digestion, solvent extraction, and isopycnic centrifugation. As indicated by the binding of kingdom-specific hybridization probes to the purified DNA, the Sargasso Sea picoplankton in this collection were largely eubacteria.

Fluorocarbon-encapsulated oxygen bubbles for blood oxygenation use: An experimental study

This paper is concerned with a novel class of oxygenators which Li and Asher first proposed and called "liquid membrane oxygenators." They are different from usual bubble blood oxygenators in that oxygen bubbles are individually encapsulated by a liquid fluorocarbon membrane and dispersed in blood, instead of bare oxygen bubbles normally used. The fluorocarbon membrane's role is to prevent direct contact of blood with oxygen gas which can cause a rupture of red blood cells and denaturation of proteins in blood. We have attempted to produce encapsulated bubbles by use of a fine double-tube nozzle where oxygen is supplied through the inner tube of the nozzle while a liquid fluorocarbon is supplied through the annular space between the outer and the inner tubes. This device has been found to enable steady formation, both in pure water and in an aqueous solution of bovine serum albumin, of encapsulated bubbles of about 2 mm in diameter, which are far smaller than those produced by Li and Asher's original device. A comparative study of oxygenation of water (a substitute for blood) by encapsulated bubbles and by nonencapsulated bubbles indicates that the former is only slightly inferior to the latter.

Porous membrane-based diffusion scrubber for the sampling of atmospheric gases

A diffusion scrubber, employing a porous fluorocarbon membrane as the sampling tube and with a scrubber solution flowing into a narrow annular space exterior to the membrane, is described. The use of this diffusion scrubber with a dilute buffered formaldehyde solution as the scrubber solution has been exploited for collecting sulphur dioxide. Collection efficiencies are reported for sampling rates of up to 3 l min–1. The response time to a SO2 input pulse in the continuous analysis mode is demonstrated using dilute hydrogen peroxide as the scrubber solution and a conductivity detector. The advantages of a diffusion scrubber for collecting atmospheric gases are discussed. A simple inexpensive design of permeation tubes for standard gas sources is also reported.

High purity fibrous air sampling media.

Interest in measurement of low concentrations of metal levels in suspended particulate matter has generated needs for high purity, low background filters. Several new types of filters are discussed with high purity compositions including glass fiber filters, fluorocarbon membranes and fabric-supported membrane filters. Air collection efficiencies are presented along with comparative analysis.