Plastics also conduct electricity
Plastics are a material that can be found everywhere in daily life, and one of their most common functions is insulation, whether it is a network of cables laid in cities or socket switches used in homes, plastic is used as an insulating enclosure on the outside of the wires. Although plastics are good insulators, scientists have found that if certain substances are doped into plastics, or plastics with special molecular structures are designed, the physicochemical properties of plastics can be changed to make them have good conductive properties.
So why do plastics conduct electricity? Scientists believe that plastics are polymers, and there are many carbon and hydrogen atoms in the molecules, which are connected "hand in hand" to a long chain. Carbon atoms have the ability to "pull" one or several electrons from each other. The ability to control electrons is relatively weak, giving plastics the potential to become semiconductors. If the plastic is doped, the carbon atom will easily be robbed of electrons by the doppants, leaving vacancies. It's like a parking lot full of cars, and once one car exits the parking lot through the exit, another car can enter. When a certain voltage is applied from the outside, the electrons near the vacancy in the polymer molecule will enter the vacancy and create a new vacancy, and this alternating continuation will cause an electric current to make the plastic a conductor.
Don't underestimate conductive plastics, which are Nobel Prize-worthy scientific discoveries and have an interesting story behind them. In September 1967, Hideki Shirakawa, a chemist at the University of Tokyo in Japan, was working on a cutting-edge science - making plastics conduct electricity. In the lab, Shirakawa supervised a South Korean graduate student studying the polymerization of acetylene. Since the experiment was not difficult, the graduate student also studied with him for a while, so Hideki Shirakawa was relieved to let the students complete the operation independently. But the experiment seemed to fail, and the South Korean graduate students were given a shiny, silvery film-like substance, which was very different from the powdered acetylene polymer that Shirakawa had envisioned. It turned out that the Korean graduate student was not very good at Japanese, and he did not listen to Hideki Shirakawa's instructions before doing the experiment, and the concentration of the catalyst mixed in was increased by 1,000 times. Despite the errors, Shirakawa decided to test the conductivity of the experimental products, and it turned out that the acetylene polymer film was surprisingly conductive.
Hideki Shirakawa was very encouraged by this accidental experiment, and he felt that he had chosen the right direction for his research. After 10 years of continuous efforts, in 1977, Hideki Shirakawa officially published a method for preparing a highly conductive film-like acetylene polymer, which doped the acetylene polymer film with iodine1 to improve the conductivity of the film to the level of metal. Shirakawa's scientific discovery changed the notion that plastics cannot conduct electricity, and he was awarded the Nobel Prize in Chemistry in 2000.
Plastic RFID tags
Nowadays, the research of conductive plastics is developing rapidly, and a number of technologies have entered the application stage. The simplest and most practical technology is "plastic RFID tag".
RFID is the abbreviation of radio frequency identification technology, which allows non-contact data communication between the detector and the tag to achieve the purpose of identifying the target. Radio frequency identification technology is widely used, the most typical is supermarket management. If a detector is placed at the exit of the supermarket and an RFID tag is attached to the product, then when the customer finishes shopping in the supermarket, there is no need to wait in line for the cashier, and the customer can directly push a cart full of goods past the detector, and the total amount of the product will be displayed in just a few seconds.
The benefits of RFID technology are obvious, but the cost of tags can be a bottleneck to the adoption of this technology. At present, RFID tags are mostly made of semiconductor material silicon crystals, and their cost is as high as a few yuan per piece, which is insignificant for automobiles, home appliances and other valuable goods, but it becomes unbearable for many low-priced goods in supermarkets. As a result, scientists have come up with the idea of replacing traditional silicon crystalline materials with cheap conductive plastic films, such as an organic material called pentabenzene. The molecular structure of Pentabenzene consists of five benzene rings, which are neatly arranged in a straight line. Scientists have found that such a molecular structure makes Pentabenzene a good semiconductor in its high-purity state, and its conductivity is close to that of silicon crystals. Using the mature chemical vapor deposition method, it can produce a large number of high-performance pentabenzene films, and use it to make RFID tags, and the cost can be reduced to a few cents per piece.
However, the information storage capacity and chemical stability of Pentaphene RFID tags cannot be compared with silicon crystals, and they need to be further optimized. If these shortcomings are solved, plastic RFID tags will quickly occupy the market, and at that time, large-scale unmanned supermarkets that can be easily settled will usher in spring.
Flexible display and "paint battery".
Have you ever wanted to have a tablet that can be curled like film, or that you can flip it over like a newspaper while playing with your smartphone? Scientists believe that organic thin-film transistor technology can make such wonderful display devices.
Organic thin-film transistors, also known as plastic transistors, differ from traditional MOS transistors (i.e., metal-oxide-semiconductor transistors) in that plastic transistors use all organic semiconductor materials, and the displays made of them have very good flexibility. Scientists have found many organic semiconductor materials that can be used in plastic transistors, such as fullerenes with carbon-60 structure, carbon-70 and some carboxylic acids are often used as n-type semiconductor materials (relying on electrons to conduct electricity); P-type semiconductor materials (which rely on vacancy conductivity) are more abundant and include a wide variety of polymers and metal complexes (which can be understood as metal-doped organic compounds), including the aforementioned pentabenzene.
The "electronic paper" developed by Japan's Sony, Toshiba and other companies is a representative work of conductive plastics for flexible displays. Sony's newly launched e-paper DPT-CP1 is the size of A5 paper and 5 thick9 mm, weighing 240 grams, it can be used as a display for entertainment, and can be written and read as comfortably as ordinary paper, powerful, ultra-thin and lightweight, and the price is around thousands of yuan.
In addition to being used as a flexible display, organic semiconductor materials can also be used to make solar cells. We can see huge solar panels on satellites and spacecraft, but the solar cells we encounter in life are often limited to small electronic devices such as calculators and watches, because traditional silicon solar cells are too expensive and complex to manufacture. In contrast, solar cells made of plastic film will have a broader prospect in life. Many polymer batteries are inexpensive, easy to manufacture, lightweight, bendable, and even "printed" on a variety of surfaces.
For example, scientists used an organic material called poly-3-hexylthiophene (P3HT) to make a plastic sheet hundreds of nanometers thick, and inserted cadmium selenide nanorods as electrodes on both sides of the sheet to make a sandwich-shaped plastic solar cell. When sunlight hits this battery, it can convert 6% of solar energy into electricity. The conversion efficiency may not sound very satisfying, but the plastic battery is so thin that it can be "brushed" on the outside of each building like paint, so the energy produced is considerable. Ideally, if the conductive plastic could be as colorful as ordinary paint, and we could wear solar cells on our bodies, the problem of powering the electronic devices we carry with us might be solved.
Robotics** and e-Health
Conductive plastics have more exotic applications, such as in robotics. Takao Someya, a scientist at the University of Tokyo, implanted an array of Pentaphenylene organic thin-film transistors under pressure-sensitive rubber, transforming it into a pressure-sensitive robot
In the experiment, scientists first made a 100 square centimeter plastic film bottom plate, on which there are about 1,000 "arrays" composed of organic thin-film transistors, and decoders are installed around the "arrays" to read the resistance values of the "arrays", and then the scientists coat a layer of pressure-sensitive rubber that can feel the pressure above these "arrays", and make a piece of artificial ** with 1,000 "pain points". When a part of the artificial ** is under pressure, the pressure-sensitive rubber will be deformed to reduce the resistance value of the "array" it covers, and then the decoder will feed back the information of the pressure of the "array" to the computer, which will make the robot feel the sense of touch.
What excites scientists is that conductive plastics can be used not only to make **, but also to make "muscle". Using polyacrylate rubber, scientists can synthesize a conductive plastic called an "electroactive polymer" that, when electrically applied, expands or contracts, creating a mechanical force. Using "electroactive polymers", scientists can make robots more agile and maneuver, which will be a breakthrough in improving the capabilities of robots.
The medical field is also where conductive plastics can come into play. Using a conductive plastic material called povinacelamide, American scientists have developed an "electronic tattoo" that can monitor the heart. This "electronic tattoo" is actually an ultra-thin, stretchable sensor powered by a mobile phone, only 28 microns thick, and able to fit snugly on the wearer's chest. In the experiment, scientists attach an "electronic tattoo" to the surface of the wearer's heart, and when the wearer's heart beats and causes the chest cavity to vibrate, the sensor can generate an electrocardiogram of the wearer and transmit it to the mobile phone. Currently, scientists are working to improve the data collection and storage capabilities of this "electronic tattoo", as well as how to carry out wireless data transmission. Considering that many conductive plastics are harmless to humans, scientists also plan to develop artificial cochlear implants and artificial nerve cells that can be implanted in humans for neurological diseases such as hearing loss, epilepsy and Parkinson's disease.
It is believed that in the future, conductive plastics will find a place in more scientific and technological fields.