Silver Membrane Filters Play a Part in Antimatter Trapping

If you fastidiously watch “Through the Wormhole” like I do, chances are you’ll find this application for silver membrane filters fascinating – they’re being used to assist in the collection of antimatter! Now if your main reference for antimatter is a certain Dan Brown novel, you should know that separating and collecting antimatter is a much, much more difficult process than the entertainment industry would have you believe. In fact, “If you take all the antimatter produced in the history of the world and annihilated it all at once, you wouldn't have enough energy to boil a pot of tea,” according to Harvard physicist Gerald Gabrielse. Professor Gabrielse is a leader in antimatter trapping methodology and a co-author of the paper Pumped Helium System for Cooling Positron and Electron Traps to 1.2 K, which details how our filters are used to trap antimatter.

Antimatter is composed of the exact opposite particles (particles of the same mass but opposite electrical charges) as its traditional counterpart. So whereas a hydrogen atom is made of one electron and one proton, an antihydrogen atom (called H-Bar) is comprised of a positron and an antiproton. When antimatter comes into contact with matter, even air, both particles annihilate and release energy in the form of photons (light particles) and/or radiation. Because of the extreme instability of antimatter, one of the major challenges with studying it is gathering enough of the material in a lab. To store any amount of antimatter requires an extremely powerful vacuum to prevent it from coming into any contact with matter. To this end, scientists are experimenting with all manner of “traps” in order to separate and analyze the antimatter.

It is one of these traps that pure silver membranes have found a role in the antimatter collection process. The paper referenced above explains how in order to collect antihydrogen the scientists must cool the trap apparatus to temperatures close to absolute zero. To cool the apparatus to such an extreme degree the scientists here use liquid helium (which is about -269°C), this is also where the silver filters come into play. In order to remove any impurities that could cause clogging in the apparatus, the liquid helium is twice filtered through silver filters, first through a 5 micron filter and then a 3 micron filter before continuing through the pumping system.

A popular misconception about antimatter is that it has potential as an alternative energy source. On his website Professor Gabrielse points out that “No antimatter energy source will ever be possible since it takes much more energy to make antimatter than can ever be recovered from antimatter annihilation…Our motivation for trapping antimatter is to study is basic properties and to compare them with the properties of ordinary hydrogen atoms.” So while this research isn’t going to solve our energy problems, it could help physicists answer some of the biggest mysteries regarding the makeup of the universe.

That last part would sound better coming from Morgan Freeman…

Visit here to find the full paper.

To learn more about antimatter trapping, including separating the myths from the facts, see Gabriel Gabrielse’s website.

What the Crap?

Biogas, a form of renewable energy this is produced through, among other things, animal and human waste (hey, it’s not like you were using it) is one of several developing energy sources whose proponents are exploring membrane separation techniques to improve their purification process. A recent study published in the “Applied Chemistry – A Journal of the Society of German Chemists” experimented with a new method of membrane separation called the “condensing-liquid membrane” (or CLM) in an effort to enrich raw biogas, which typically contains between 50-80% methane, to natural gas quality (at least 95% methane content), with favorable results.

Common membrane materials like Cellulose Acetate and Polyimide have been tried for this application with some success, but the problem is that they can be ruined by the aggressive gases that are present in raw biogas, such as carbon dioxide and hydrogen sulfide. The CLM is a liquid (water in this case) layer that condenses on a porous hydrophilic membrane which then gets regenerated to allow for continuous operation. This support, made from Teflon, gathers water vapor from the biogas on the feed side of the membrane and is partially removed from the permeate side by nitrogen gas, thus allowing for separation to occur in one step as the water is constantly refreshed. One of the more brilliant aspects of the CLM method is that the presence of water in biogas, usually regarded as a disadvantage, suddenly becomes a key component in the process.

Since the membranes are being preserved and not destroyed, the potential exists for this process to be a cost-efficient method of purifying biogas in the future. Researchers will continue to investigate the CLM method in order to find the optimal conditions that will make it even more efficient.

Visit here to read the full report “Effective Purification of Biogas by a Condensing-Liquid Membrane.”

To learn more about biogas, try this site from Alternative Fuels and Advanced Vehicles Data Center and the U.S. Dept. of Energy.

How does a biogas plant work? Watch this animated video to get an idea.

Deadliest Catch: Man-Made Pollution

Cruising around the Scandinavian coastline in November might not sound like the most ideal place to conduct an environmental impact study, but for Norway’s Institute of Marine Research it was necessary in order to investigate the levels of anthropogenic particles in the Skagerrak strait. As you can imagine, this setting presented some unique challenges for the research team. In order to gather and analyze microscopic samples from this body of water, which is located between Norway, Denmark and Sweden, researchers had to come up with some new sampling methods and fashion their own equipment to solve problems that had plagued previous studies.

Norwegian Researchers Hard at Work^

One key obstacle that these scientists needed to overcome was how to distinguish between anthropogenic particles, which are man-made bits of matter that impact the environment (i.e. oil-spill droplets, asphalt, rubber tire wear, fly ash), from those particles with similar characteristics which appear naturally (volcanic ash, peat). To make this distinction, the samples were subjected to morphology analysis of their color and texture to first determine their origin before being counted.

The second major challenge was how to prevent contamination, which is easier said than done considering the harsh and unpredictable nature of the sea. One of the steps the researchers took to solve this was to develop control samples, free of any contaminants, which they could actually bring on board the ship with them. To further reduce the potential of contaminating samples, they also created new methodology and constructed their own customized sampling apparatus.

You can see a schematic of the sampling equipment the Institute researchers built in their published study. Their setup involved a submersible water pump that was positioned inside a waterproof case connected to the sampling filter (10 μm hydrophobic polycarbonate membrane filters, along with a 30 μm square mesh nylon filter as a support) which was placed directly in the sea. To protect the filter from wave turbulence they modified one of our filter holders (this one) with a new outlet fitting and a larger, semi-enclosed inlet with a smooth surface. The filters were also placed in protective holders before and after filtration for protection and to reduce the risk of contamination. As an added protective measure, the filter apparatus was ultrasonically cleaned prior to use. The entire sampling apparatus was held 2 meters outside the boat (to further prevent contamination) and the sampling depth was limited to between 0.1 and 1.5 meters to protect it from large waves.

While it will take many more studies before conclusions can be drawn about the state of this particular body of water, the scientists were encouraged by the results of the new methodology they created. They note in the conclusion how these improvements have standardized the sampling and reduced the risk of contamination. The scientists also suggest that this sampling equipment could be adapted for larger particles.

To read the full study, visit here.
^Image from Survey of microscopic anthropogenic particles in Skagerrak. Lysekil and Flødevigen 2010-11-20, Institute of Marine Research.

Enhancing UF Membranes with Carbon Nanotubes

One of the most promising new frontiers in filtration technology involves infusing different membrane types with nanomaterials in order to improve performance or to pass along certain material attributes. Here we will look into one prominent example from recent years, the incorporation of carbon nanotubes (CNTs) into ultrafiltration membranes used in water treatment. We’ll also look at how our stirred cells have aided in this specialized membrane manufacturing process.

First off, what is there to gain by using CNT’s to manufacture water treatment membranes? While scientists have identified several potential advantages for CNT implementation, since the process is still in the R&D phase they have not necessarily been proven in all cases. One key possible benefit is that membranes made with these materials would be much stronger than traditional membranes, thus reducing instances of membrane breakage and fouling, two problems that contribute significantly to high maintenance costs in water treatment. Another unique advantage is that CNTs have antibacterial properties that may reduce biofilm formation and therefore prevent or limit biofouling. Lastly, the process of manufacturing ultrafiltration membranes with CNTs allows the producer to chemically modify the membrane surface which can further reduce fouling by tailoring the membrane for specific organic solutes.

As with standard membrane manufacturing processes, the stirred cell is an ideal piece of equipment for establishing the permeability of the test membranes. For this particular study on the effectiveness of polysulfone ultrafiltration membranes manufactured with CNTs, the cell (an HP4750 in this case) was set to perform dead-end filtration with ultrapure water at 38 bars of pressure (about 551 psi).

The HP4750 Stirred Cell

In order to determine permeability, the HP4750 was directly connected to the pressure regulator of the compressed air tank. Each membrane was compacted at 38 bars until the flow rate was stable (minimum of 30 minutes). Then the flow rate was measured by weighing the permeate as a function of the pressure applied (between 5 and 35 bars). To confirm the results, this test was performed in triplicate.

Permeability is an important test characteristic for determining the membrane’s susceptibility to fouling and its overall efficiency. In the study cited here, researchers found no statistically significant difference in permeability between CNT and non-CNT amended membranes. These findings supported their conclusion that their process for grafting CNTs onto membranes was ineffective. In the conclusion the authors note that because the CNTs only partially dispersed in the host material that they were prevented from taking on the mechanical properties of the CNTs.

While this particular study did not yield the desired results, new methods of integrating nanomaterials onto membranes are constantly being explored and hopefully it’s only a matter of time until these superior membranes become available.

Visit here to read the full study:
http://cohesion.rice.edu/engineering/pedroalvarez/emplibrary/85

Do You Trust Me?

According to a recent survey from Laboratory Equipment magazine on the usage of meters and monitors in lab experiments, most researchers do in fact trust their instrumentation; only 1% indicated that they were dissatisfied with their existing equipment. Another sign of trust: 71% of respondents plan to purchase direct replacements for their existing products when they buy new equipment.

You can take a look at these charts on what sort of meters and monitors are beings used and what they are being used for.

New Hydrogen Gas Sensing Method Uses Commercially Available Membrane Filters

Scientists at Northern Illinois University recently published a new approach for fabricating hydrogen gas sensors by depositing palladium onto commercially available filtration membranes.  This creates networks of ultrasmall palladium nanowires without the traditional obstacles of nanofabrication (tedious production, potential contamination).  Palladium, besides poisoning Iron Man, is highly selective to Hydrogen gas and therefore commonly used in room-temperature solid-state Hydrogen sensors.

The new method involves a network of ultrasmall palladium nanowires (<10nm) being placed on 60 micron thick membranes with a nominal filtration pore diameter of 20nm. The end result is that this new type of fabrication method outperformed traditional hydrogen sensors, such as continuous reference film, by providing higher sensitivity and shorter response times. Better hydrogen sensing can lead to greater efficiency in areas such as steel manufacturing and clean energy research.

Performance Improvement of Cross-flow Filtration for High Level Waste Treatment

The Department of Energy and Savannah River National Laboratory recently published a study regarding their efforts to improve performance on cross-flow filtration for high level waste treatment. Even though the waste being treated in this case is actually radioactive material from nuclear power plants, the process they describe, along with the issues they raise and recommendations for improvement, can be applied to the more common uses for cross-flow filtration.

The stated goal of this DOE research was to improve filter fluxes in their existing cross-flow equipment, a common request of many customers. The study examines the problem of increasing cross-flow filtration efficiency from a number of different approaches: Backpulsing, cake development, scouring, and cleaning were all taken into consideration.

At the end of the study SRNL was able to draw some conclusions to take into consideration when evaluating your own setup.

• Higher solids concentration presents a greater challenge to filtration.
• The presence of a filter cake can improve the solids separation by an order of magnitude as determined by turbidity.
• Scouring a filter without cleaning will lead to improved filter performance.
• Filtrate flux decline is reversible when the concentration of the filtering slurry drops and the filter is scoured.

You can read the full report here to see a detailed description of their setup and complete results.

FAQ: Black Polycarbonate Membranes

When counting bacteria as part of epifluorescent microscopy we generally recommend using the black polycarbonate membranes instead of cellulose membranes. This is because the black polycarbonate materials have a uniform pore size and flat surface that will retain all of the bacteria without trapping any inside of the filter. Though cellulose membranes will retain bacteria, it often will become trapped inside of the filter, where it cannot be counted.

Polycarbonate Filters in Legionella Detection

Recently one of our customers was interested in testing Legionella bacteria and asked us how our polycarbonate membranes fit into the process mentioned on our website. If you are unfamiliar with Legionella, it is a waterborne pathogen commonly found in aerosolized waters such as cooling towers, showers, and humidifiers, and it is best known as the cause of Legionnaire’s Disease as well as Pontiac Fever. Its name originated from an outbreak that occurred at the 1976 convention of the American Legion in Philadelphia.

There are actually two areas in which membranes are used in regards to Legionella: Sample preparation and point-of-use filtration. For sample preparation the CDC (Centers for Disease Control) recommends using a 0.2 micron, 47mm polycarbonate filter to extract Legionella bacterium from potable water. Non potable water utilizes a direct plating procedure.

Point of use filtration frequently involves a device that attaches to a faucet or showerhead to eliminate Legionella. Such devices have filters built into them, usually made of Nylon or PFT. A few years ago the American Journal of Infection Control conducted a study of these devices and found them to be extremely effective at preventing the spread of waterborne pathogens.

For more information on Legionella testing and guidelines, you can visit:

http://www.cdc.gov/legionella/files/legionellaprocedures-508.pdf
http://www.specialpathogenslab.com/SPL-Advantage/AJICFilterpaper05.pdf

ASTM Standards for SDI Testing

The good people at ASTM (American Society for Testing and Materials) have released their standard for determining the Silt Density Index of water. If you're interested in learning more about it, you can preview the document here. You can also look at our very own SDI test kits here.

Putting on a Shiny Suit: Polycarbonate Membranes get Sputtered!

Polycarbonate (PCTE) track-etch membranes, created decades ago, are finding some new uses in the development of nanotechnology applications.  They owe this new application to their precise pore geometry and organization.  PCTE membranes were previously utilized in the manufacture of single-walled nanotubes (SWNT) due to the relative ease of depositing metal ions on the inside of their pores, then selectively dissolving the PCTE; leaving behind nanotubes for use as super-conducting wires, micro-diode arrays, or magnetic-data storage devices.  

PCTE membranes are traditionally sputter coated with gold for use in scanning electron microscopy (SEM) imaging because it is easier to capture samples on their smooth membrane surface.  Now scientists are developing new ways to utilize PCTE membranes by sputter-coating metal ions on the membrane.  One new use is to construct a biocompatible glucose sensor¹ that can be implanted inside a diabetic’s body.  The membrane is sputter coated with platinum and the pores filled with an enzyme chemically anchored inside the pore.  When excess glucose enters the pores, an electrochemical reaction is started, traveling down the pore to the thin sputtered metal layer, where the signal is picked up and sent to a microprocessor inside the sensor.  The amount of glucose triggering inside each pore determines the strength of the electrical response.  The size of the entire sensor area might be as small as 0.15cm²!  There’s even work filling PCTE pores with photosensitive materials to turn the membrane into flexible solar cells.   

Sputtered membranes are also finding niches in synthesizing catalysts to help make ethanol from syngas (CO and H₂) as this ethanol can be used as an inexpensive and environmentally friendly fuel and fuel additive².  PCTE sheets can be sputter coated with gold and sandwiched onto a Zn sheet to make the necessary anode and cathode for electrodepositing Mn-Cu-ZnO nanowires/tubes.  These nanotubes can then be successfully used as catalysts in CO hydrogenation reaction to produce alcohols.  With so many industrial nations moving towards ethanol as an alternative to petroleum fuels, the need for synthesizing ethanol from available materials may have a new ally in track-etch membranes.

1: A. Kros, M. Gerritsen, V.S.I. Sprakel, N.A.J.M. Sommerdijk, J. Jansen, R.J.M. Nolte, Silica-based hybrid materials as biocompatible coatings for glucose sensors. Sensors and Actuators B, (2001) 68-75.

2: M.Gupta1, V. Kalpathi and J. J. Spivey, Electrodeposition of Cu-ZnO and Mn-Cu-ZnO Nanowires/tubes for Synthesis of Ethanol [abstract] In: Proceedings of the Electrochemical Society, 214^th Meeting Honolulu, Hawaii. October 12-17, 2008.  Abstract no. 0281

FAQ: Clarification of Fruit (Apple) Juice

Over the years we have seen an increased use of filtration equipment in juice processing, particularly regarding ultrafiltration (UF) or microfiltration (MF) for the clarification of apple juice.  Since it has been demonstrated that membrane filtration can produce yields of 95%-99% - compared to only 80-94% through conventional processes – it is no wonder that filtration methods are growing in prevalence.  The greater yield combined with the reduced time and labor costs have translated to hundreds of thousands of dollars saved for juice processing plants!

If you are considering juice filtration, here a couple of tips to keep in mind:

• The juice must be clear.  Of the four common types of apple juice produced – natural, crushed, clarified, and clear – only clear juice is suitable for membrane processing.    
• Consider ceramic membranes.  More and more fruit juice installations are installing ceramic membranes.  While these do have  a higher cost than other materials, they do offer a higher flux, much longer life, and better resistance to aggressive processing and cleaning conditions. 
• Know your operation.  Since fruit juices have a very low level of retained solids, the optimum mode of operation is the modified batch operation with a partial recycle of retentate.
• Not just for apples.  Other fruit and vegetables that have benefited from membrane filtration include: apricot, carrot, cherry, cranberry, grape, lemon, lime, orange, peach, passion fruit, and tomato.

References:
Ultrafiltration and Microfiltration Handbook.  Cheryan, Munir.  Technomic Publishing Company, 1998.
Microfiltration and Ultrafiltration: Principles and Applications.  Zemon, Leos & Zydney, Andrew.  Marcel Dekker, 1996.

Water Sterilization & Silver

From this recent article in NanoLetters, the American Chemical Society Journal, comes information about a new form of water sterilization out of Stanford University that takes advantages of the unique bacteria-killing properties of silver (the vampire and werewolf killing properties of silver have yet to be proven).  Basically, the proposed multiscale device would perform high speed electrical sterilization of water using a combination of silver nanowires, carbon nanotubes, and cotton.  The end result is that when operating at 100,000 L/(h m²) this device can inactivate greater than 98% of bacteria with only several seconds of total incubation time.

The author’s of this paper mention two interesting reasons for why silver is used in the device.  The first:        

Taking advantage of silver nanowires’ (AgNWs) and CNTs’ [Carbon Nanotube] unique ability to form complex multiscale coatings on cotton to produce an electrically conducting and high surface area device for the active, high-throughput inactivation of bacteria in water.

The other reason described for using silver in water sterilization:

Silver is chosen since it is a very well-known bactericidal agent, and recently a large amount of interest has been spurred by the discovery that silver nanoparticles work extremely well at killing bacteria and can be attached to various surfaces with chemical techniques.    

The outcome of the silver treatment in the author’s experiment provides further evidence of these properties:

The results clearly show that filters not treated with silver, including CNT-only cotton, showed a robust growth of bacteria, while the bacteria concentration in the solutions incubated with AgNW-treated material was reduced to the detection limit of the absorbance system used, at least a 2 to 3 order of magnitude reduction.

All in all, the findings in this paper are encouraging that implementation of this approach can kill microorganisms which cause biofouling in downstream filters.  The authors of the paper state, “Such technology could dramatically lower the cost of a wide array of filtration technologies for water as well as food, air, and pharmaceuticals, where the need to frequently replace filters is a large cost and difficult challenge.”

Their next step is to expand their experimentation to other microorganisms beyond the E. coli that was used for this study.  In their conclusion the authors note that, “Silver is known to be an extremely general agent so it can be expected that this device will also work over a wide array of organisms.” 

We’ll continue to monitor their progress and hope for the best!

New Technique to Improve Crossflow Filtration

One of the biggest issues for crossflow filtration is figuring out how to control the loss of permeate flux in the process. Whether using reverse osmosis (RO), ultrafiltration (UF), or microfiltration (MF), the loss due to polarization and membrane fouling prevents many potential users in the biological or chemical processing fields from adopting this method.

If you are using crossflow filtration, or considering using it, and fear the effects of permeate loss, then you may want to consider this technique courtesy of North Carolina A&T University and the U.S. National Energy Technology Laboratory. Their study (see here) produced drastically improved results by implementing flow reversal to enhance the membrane flux.

They found that by periodically reversing the flow direction of the feed stream at the membrane surface results in prevention and mitigation of membrane fouling. This particular study conducted experiments with bovine serum albumin, Detran T-70, and apple juice. We’d love to hear from any of you in the field that may have tried this technique to see how it worked out!