SCIENCE TRIBUNE Thursday, November 1, 2001, Chandigarh, India
 


Electricity-conducting plastics
S. S. Verma

G
ONE are the days when we used to teach the difference between conductors and bad-conductors/insulators by giving examples of metals and plastics, respectively. Today plastics are made to conduct electric current and in future who knows they may exhibit magnetic properties also.

NEW PRODUCTS & DISCOVERIES

  • An aircraft like no other

  • Love is in the air

  • Automated warehousing

  • Novel biochip for drug testing

SCIENCE QUIZ
J.P. GARG TESTS YOUR IQ

 
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Electricity-conducting plastics
S. S. Verma

GONE are the days when we used to teach the difference between conductors and bad-conductors/insulators by giving examples of metals and plastics, respectively. Today plastics are made to conduct electric current and in future who knows they may exhibit magnetic properties also. Research and development in properties of plastics have already brought them very close to metals in terms of their mechanical properties viz., strength, elasticity and molding etc.

By virtue of their chemical makeup, plastics have no business of conducting electricity. But in the 1970s, scientists discovered that impurities added to certain polymers made it possible for them to carry small electrical currents. The first electrically conductive plastics became a scientific sensation when they were created in the late ’70s by Alan J. Heeger, now at the University of California (USA) at Santa Barbara, Alan G. Mac Diarmid of the University of Pennsylvania (USA), and Hideki Shirakawa of the University of Tsukuba in Japan. These researchers demonstrated that the polymer polyacetylene could be doped so that its conductivity increases a trillion times and reaches the conductivity of metallic copper. This discovery won them the 2000 Nobel Prize in chemistry and further spawned a new generation of inexpensive, flexible plastic electronics.

The electrically conductive plastics have attracted a substantial amount of attention since they were accidentally discovered two decades ago and the race is on to invent new conductive plastics with many great expectations from them (conducting plastics). Conductive plastics are long, carbon-based chains composed of simple repeating units called monomers. Conductive polymers are much more electrically conductive than standard polymers but much less than metals such as copper. In practice, the conductivity of these materials is characterised by low-charge carrier mobility — a measure of how easily electric charge moves. The most extensively studied conductive-polymer systems are based on polyaniline, polythiophene, polypyrrole, and polyacetylene. The principal attractions of these polymers over conventional conducting materials are their potential ease of processing, relative robustness, low cost, flexible and lightweight nature.

Though the list of potential applications for conductive polymers remains a long one, and includes antiradiation coatings, batteries, catalysts, deicer panels, electrochromic windows, electromechanical actuators, embedded-array antennae, fuel cells, lithographic resists, nonlinear optics, radar dishes, and wave guides etc. Just how big an impact the materials will make in these markets remains unclear, however. Here a few of them are being highlighted.

  • The most significant commercialisation of conductive polymers is for flexible, long-lived batteries.

  • Development of a fibre. The fibre is coated with a conductive-polymer material called polypyrrole and can be woven to create an antistatic fabric to be used in carpet products.

  • Polypyrrole had been approved for use in stealth attack carrier aircraft. It has to be used in edge cards — components that dissipate incoming radar energy by conducting electric charge across a gradient of increasing resistance that the plastic material produces.

  • To produce conductive-polymer electromagnetic shielding for the space applications.

  • The opportunity to produce relatively low-cost semiconductor devices that are insensitive to mechanical deformation is an attractive one. Probably the most exciting development in this area is the intensifying effort to use conductive polymers to produce flat, flexible plastic screens for TV and computers. This screen technology emerged from the discovery that certain conductive polymers, such as polyDp-phenylenevinylene, emit light when sandwiched between oppositely charged electrodes, a configuration that fits in well with current flat-panel display designs. While it is likely to be some time before this technology makes it to the market in flexible flat-panel screens, the development work has created a whole new buzz about conductive polymers.

  • Another promising application is in capacitor technology to develop ultracapacitors for future electric vehicles. Conductive polymers can provide lower equivalent-series resistance (ESR). Thus, with the designers of mobile electronics constantly being pushed for space, the new capacitors can simultaneously be smaller and have a lower ESR.

  • Yet another emerging application for electrically conductive polymer materials is biosensors and chemical sensors, which can convert chemical information into a measurable electrical response. The challenge is how to confer specificity to these materials.

  • An area with some further-off potential — smart membranes of conductive polymers — is also being pursued to develop engineered porous fibre materials with electrically controlled porosity using polyaniline. The technology could find use in gas separation, pharmaceutical separation, environmental clean-up, batteries, or capacitors.

  • Recently, researchers have found a way to make polymers conduct electricity with virtually no resistance at very low temperatures. Eventually, it could lead to the manufacture of plastic components for a new generation of ultra-fast components that would be based on quantum mechanics. These superconducting polymers could be used to create superfast "quantum" computers and other superconducting electronic devices. Who knows? We may one day have supercomputers based on superconducting plastics.

  • "Plastic" light-emitting diodes (LEDs) can Deliver More Light. It is concluded by the researchers that electrically conducting plastic could convert 45 per cent of more of electricity into light. Until now, the maximum efficiency for LEDs was thought to be about 25 per cent.

Thus, the future looked a lot brighter for conductive polymers. No doubt conducting plastics have a huge potential but yet to make many inroads. Successful commercial applications of these polymers, however, require a fine balance of conductivity, processability, and stability, but until recently, materials researchers could not obtain all three properties simultaneously.

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NEW PRODUCTS & DISCOVERIES

An aircraft like no other

A Silicon Valley aerospace company has announced that it has achieved an important milestone while testing its paradigm-shifting new product, Solo Trek XFV. The full-scale Solo Trek proof-of-concept prototype aircraft produced over 100 per cent take-off power and thrust for the first time in its development programme, thereby validating earlier predicted performance. "This sets the stage for tethered-hover testing to begin in the mid-to-late summer timeframe," said Michael Moshier, chief executive and chief technical officer.

Solo Trek is an open-air VTOL (vertical take-off and landing) aircraft that will transport a person in an upright and standing position for up to two hours. Using readily available fuel, Solo Trek is predicted to attain speeds in excess of 70 miles per hour and is designed to operate easily in and out of extremely confined areas.

High-power system testing is currently underway at Millennium Jet’s Sunnyvale headquarters. "We instrumented the aircraft with strain gauges and secured it to the ground," said Moshier, "then we were able to bring the engine, drivetrain and ducted fans up to about 105 per cent take-off power and thrust without exceeding 75 per cent throttle. Achieving this critical milestone demonstrates that Solo Trek can generate sufficient take-off thrust while maintaining an adequate power reserve. It also proves the capability of the vehicle’s gear boxes and drive shafts to perform well under high load without overheating or noticeable vibration."

DARPA (a Department of Defence research agency) recently granted the company over $5 million in funding for a 36-month period, beginning last December. "DARPA’s willingness to get behind the Solo Trek programme," said Harry Falk, chief financial officer of Millennium Jet, "shows a great deal of confidence in our technology and engineering. With its continued assistance, we expect to complete the remaining development and testing work sooner than we otherwise could." The agreement with DARPA calls for a Solo Trek first-article prototype to be delivered to the USSCOM (United States Special Operation Command) in late 2003 for rigorous field evaluation.

Love is in the air

In future, people in search of right life partner might use a new device, "e-nose", to "smell" and make an intelligent choice.

Researchers in Germany have developed an electronic nose that can detect the smells that mice use to choose mates with compatible genes. The device should make it easier to test the controversial idea that people also rely on smells, and that having the wrong ones may sometimes sow the seeds of divorce, a report in New Scientist says.

Rodents sniff their suitors to see whether they have the same major histocompatibility complex genes as their own. MHC genes code for proteins in the immune system, and the more diverse they are, better the chances of coping with new infections. So rats and mice, at least, follow their noses and choose mates with different MHC genes, to endow their offspring with a varied portfolio.

Until now, researchers have not been able to directly measure difference in smells associated with MHC genes. They have relied on rodents to do this for them in behavioural experiments. But Hans-Georg Rammensee and his colleagues at the University of Tubingen have built an electronic nose that does the job.

The e-nose has two components. The first contains a series of eight tiny quartz crystals coated with different polymers. Odour molecules stick to particular coatings, and just a few molecules will change the frequency at which the crystal vibrates. The second part uses a series of semiconducting metal-oxide gas sensors. Gases react with oxygen on the sensor surfaces and change their conductivity. Both components are hooked up to a computer that can recognise the patterns of each small. "It’s very sensitive — it can distinguish, different brans of coffee, for example," says Rammensee.

The e-nose has already singled out mice with different MHC genes by sniffing their urine. And, it can also distinguish the smell of blood serum from people with different MHC genes.

The jury is still out on whether MHC smells affect one’s choice of partners. People mask MHC smells with perfumes and deodorants. So a partner might only subconsciously register them after a long exposure. Rather than being involved in the dating game. MHC incompatibility may manifest itself in today’s high divorce rate.

Rammensee suggests that sociologists could use the e-nose to test this idea, sniffing divorced couples to see if they have a higher incidence of MHC incompatibility than those celebrating their silver wedding anniversary, for example. "It is speculation," he cautions. But if the idea is confirmed, courting couples could one day be surreptitiously sniffing each other with e-noses to find out if they make a good match. PTI

Automated warehousing

To minimise the problems associated with home delivery of purchases made by customers through the Internet, scientists have developed an automated warehousing system that boasts of several advantages.

Despite the wave of bankruptcies affecting many of the dotcom firms that have shot up in such vast numbers, Internet-based commerce is an up-and-coming trend with turnover expected to rise from the present 117 billion euro to 422 billion euro by 2003.

As Internet offers the opportunity to order products at any time of the day or night, customers expect their purchases to be delivered to their homes with the briefest possible delay and without having to pay exorbitant delivery charges.

Keeping in view that customers will not forgive even the smallest mistake — neither late deliveries nor excess charges — researchers from the IML designed a solution, Tower 24, an alternative approach for customers to collect their purchases from unmanned pick-up points, such as railroad-station lockers or gas stations, a report in Fraunhofer Gesellschaft said.

The advantage of Tower 24 is that its access is easier, both for the supplier and the customer. The supplier can drive right up to the tower and aided by the ergonomic design of the input window can deposit upto 100 consignments in 20 minutes. PTI

Novel biochip for drug testing

Scientists have developed a new lab-on-a-chip detection system for athletes which can test thousands of samples of urine for dozens of illegal substances as against a few picked out for random tests, thereby promising to be a helpful aid for the next Olympics in 2004.

The Evidence system, developed by the Randox Laboratories in Crumlin, Country Antrium, relies on established antibody screening technology but scientists at the laboratory have adapted it for a silicon "biochip" one centimetre across that tests upto 25 drugs at once.

Antibodies that trap specific drugs and their metabolites — the by-products of their breakdown in the body — are attached to the surface of the chip in an array of 25 spots.

So when a single urine sample is spread across the chip, the system tests it simultaneously for all 25 substances, a report inNew Scientist said.

A flourescent "tag" substance is then washed over the chip. It binds to any antibody that has captured its target, and then emits light. The amount of light given off by each spot shows how much of each substance is present. PTI

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SCIENCE QUIZ
J.P. GARG TESTS YOUR IQ

1. Who proved for the first time that the nucleus of an atom contains uncharged particles called neutrons (for which discovery he was awarded the Nobel Prize in Physics in 1935)? Which other main fact about nuclei did he establish?

2. Continuing on the subject, although normally neutron is considered to be uncharged, modern measurements have shown that neutron has a negative magnetic moment. What does it imply? What is the probable cause of this implication?

3. Which is the most poisonous snake in the world, which is five feet long and its poison contains so much venom that it can kill 300 sheep?

4. This device consists of an electronic camera fitted on the frame of spectacles. The camera converts light signals coming from an object into electrical signals which are then conveyed to the sight area of the brain that interprets these signals as images of the parts of the object. What is this device called that enables the blind to see and was invented by Dr. Rob Webb?

5. This plant has many healing properties. When its thick and fleshy leaves are cut, they yield a sticky and transparent jel, which is its medicinal part. It has digestive, diurectic, anti-inflammatory, anti-bacterial, anti-fungal, wound-healing and rejuvenating properties. Which is this plant that attains a height of about two feet and is grown in many homes in pots?

6. Which blood group makes a person a universal donor and which blood group a universal acceptor?

7. How much is the maximum time for which a solar eclipse can last? What limits this time?

8. What is the interactive technology called which enables persons sitting at even far off places (like different countries) to talk to one another?

9. When carbon dioxide gas is passed through this 'water', a 'milky' precipitate is obtained. Which is this 'water'? What is the 'milky' precipitate?

10. A space probe sent by the US space agency NASA which reached within 2,156 km of a comet recently has revealed that this comet has a surface of rugged terrain, rolling plains, deep fractures and very dark material. Name the space probe and the comet studied by it.

Answers:

1) British physicist Sir James Chadwick in 1932; that the mass of the neutron is approximately equal to that of proton 2) Neutron has a net negative charge; neutron consists of particles (quarks) which give it a net negative charge 3. Australian tiger snake 4) Scanning Laser Opthaloscope 5) Aloe, having common names "ghrit kumai" and "ghee kunwar" 6) 'O' and 'AB' respectively 7) 7 minutes and 58 seconds; speed of the earth around the sun 8) Teleconferencing 9) Limewater (saturated solution of calcium hydroxide in water); calcium carbonate 10) Borrelly; Deep space 1.

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