The novel world after plastic conducts electricity

Plastic also conducts electricity

  Plastic is a kind of material that can be seen everywhere in daily life. One of their most commonly used functions is insulation. No matter the cable network laid in the city or the socket switch used in the home, plastic is used as the insulating shell outside the wire. Although plastic is a good insulator, scientists have found that if you dope with certain substances in the plastic, or design a plastic with a special molecular structure, you can change the physical and chemical properties of the plastic to make it have good electrical conductivity.

Hideki Shirakawa

  So why does plastic conduct electricity? Scientists believe that plastics are high-molecular polymers. There are many carbon atoms and hydrogen atoms in the molecule, which are connected to a long chain “hand in hand”. Carbon atoms have the ability to “pull” one or several electrons to each other. The carbon atoms that “pull” a few electrons have relatively weak ability to control electrons, giving plastics the potential to become semiconductors. If the plastic is doped, then the carbon atoms will easily be taken away by the dopant electrons, leaving vacancies. This is like a parking lot crowded with cars. Once a car leaves the parking lot from the exit, another car can enter. When a certain voltage is applied from the outside, the electrons near the vacancies in the polymer molecules will enter the vacancies and create new vacancies. In this way, the continuation of the alternation will cause currents and make the plastic a conductor.
  Don’t underestimate conductive plastics. This is a Nobel Prize-level scientific discovery, and there is an interesting story behind it. In September 1967, Hideki Shirakawa, a chemist at the University of Tokyo in Japan, was studying a cutting-edge science-making plastics conduct electricity. In the laboratory, Hideki Shirakawa directed a Korean graduate student to study the polymerization of acetylene. Since the experiment is not difficult, the graduate student also followed himself for a while, so Hideki Shirakawa assured the students to complete the operation independently. But the experiment seemed to have failed. Korean graduate students got a shiny, silver film-like substance, which was completely different from the powdered acetylene polymer expected by Hideki Shirakawa. It turned out that Korean graduate students were not very good in Japanese. Before doing the experiment, they did not listen to Hideki Shirakawa’s instructions, and the concentration of the catalyst added was increased by 1,000 times. Although the experiment went wrong, Hideki Shirakawa decided to test the conductivity of the experimental product, and found that the conductivity of the acetylene polymer film was surprisingly good.

Sony’s newly launched electronic paper DPT-CP1

  Hideki Shirakawa was very encouraged by the experiment of mishandling and collision, and he felt that he had chosen the right research direction. After 10 years of continuous efforts, in 1977, Hideki Shirakawa officially published a method for preparing a highly conductive film-like acetylene polymer. By doping an acetylene polymer film with 1% iodine, the conductivity of the film can be improved to The degree of metal. This scientific discovery by Hideki Shirakawa changed the concept of “plastics cannot conduct electricity” and won him the Nobel Prize in Chemistry in 2000.
Plastic RFID tag

  Nowadays, the research of conductive plastics is developing rapidly, and many technologies have entered the application stage. The simplest and most practical technology is “plastic RFID tags”.

Plastic solar cell

  ”RFID” is the abbreviation for 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, and the most typical one is supermarket management. If the detector is installed at the exit of the supermarket and the RFID tag is attached to the product, then after the customer has finished shopping in the supermarket, there is no need to wait in line for the cashier. The customer can directly push a cart full of goods past the detector, just In a few seconds, the total amount of the product is displayed.
  The convenience of radio frequency identification technology is obvious, but the cost of tags may become a bottleneck restricting the popularization of this technology. At present, RFID tags are mostly made of semiconductor material silicon crystals, and their cost is as high as several yuan per piece. This price is insignificant for expensive goods such as automobiles and home appliances, but it becomes unbearable for many low-priced goods in supermarkets. Up. Therefore, scientists have thought of replacing traditional silicon crystal materials with cheap conductive plastic films, such as an organic material called “pentacene”. The molecular structure of pentacene contains five benzene rings, which are neatly arranged side by side along a straight line. Scientists have discovered that this molecular structure makes pentacene 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, mass production of excellent pentacene films can be used 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 pentacene RFID tags cannot be compared with silicon crystals, and further optimization is needed. If these shortcomings are solved, plastic RFID tags will quickly occupy the market. Only then will large unmanned supermarkets that can facilitate settlement usher in the spring.
Flexible display and “paint battery”

  Have you ever thought about owning a tablet that can be rolled up like film, or when playing a smartphone, you can fold it up like you would read a newspaper? Scientists believe that organic thin film transistor technology can make such a wonderful display device.
  Organic thin film transistors are also called plastic transistors. They are different from traditional MOS transistors (metal-oxide-semiconductor transistors) in that all plastic transistors use organic semiconductor materials, and the displays made by them have very good flexibility. . Scientists have found many organic semiconductor materials that can be used in plastic transistors. For example, fullerenes with carbon 60 structure, carbon 70 and some carboxylic acid compounds are often used as N-type semiconductor materials (relying on electronic conduction); P-type semiconductor materials (Relying on vacancies to conduct electricity) is even more abundant, including a variety of polymers and metal complexes (can be understood as organic compounds doped with metals), including the aforementioned pentacene.
  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 electronic paper DPT-CP1, with the size of A5 paper, 5.9 mm thick, and weighs 240 grams, can be used as a display screen for entertainment, and can write and read comfortably like ordinary paper. It is powerful and ultra-thin. Lightweight, the price is around several thousand yuan.

Sunlight generates positive and negative charges on the interface between the two polymers. These poles work in the same way as the poles in ordinary batteries, but are powered by the sun.

  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 encountered in our lives are often limited to small electronic devices such as calculators and watches. The reason is that traditional silicon solar cells are too expensive to manufacture. complex. In contrast, solar cells made of plastic films will have broader prospects in life. Many polymer batteries are cheap, easy to manufacture, light in weight, flexible, and can even be “printed” on a variety of materials.
  For example, scientists use an organic material called poly-3 thiophene (P3HT for short) to make a plastic sheet several hundred nanometers thick, and insert cadmium selenide nanorods as electrodes on both sides of the sheet to make it. A plastic solar cell with a sandwich structure. When sunlight shines on this battery, 6% of the solar energy can be converted into electricity. The conversion efficiency may not sound very satisfactory, but this plastic battery is very thin and can be “brushed” on the outside of each building like paint, and the energy produced is considerable. More ideally, if this conductive plastic can be as colorful as ordinary paint, we can also wear solar cells on the body, and the power supply problem of the electronic equipment that we carry with us may be solved.
Robot simulation and electronic medical

  There are even more exotic applications of conductive plastics, such as in robotics. Takao Someya, a scientist at the University of Tokyo, implanted the pentacene organic thin-film transistor array under the pressure-sensitive rubber to transform it into the “skin” of a pressure-sensitive robot.
  In the experiment, the scientists first made a plastic film substrate of 100 square centimeters, on which there are about 1,000 “arrays” composed of organic thin film transistors, and a decoder is installed around the “array”, which can be read For the resistance value, scientists then apply a layer of pressure-sensitive rubber that can feel pressure on top of these “arrays,” and then create an artificial skin with 1,000 “pain points”. When a certain part of the artificial skin is under pressure, the pressure-sensitive rubber will deform, reducing the resistance value of the “array” it covers, and then the decoder will feed back information about the pressure of the “array” to the computer, which will Let the robot feel the sense of touch.
  What excites scientists is that conductive plastics can not only be used to make skin, but also “muscles.” Using polyacrylate rubber, scientists can synthesize a kind of conductive plastic called “electroactive polymer”. When this plastic is energized, it will expand or contract, generating mechanical force. Using “electroactive polymers”, scientists can make robots more flexible movements, which will be a breakthrough to improve robot capabilities.

  The medical field is also a place where conductive plastics can show their talents. US scientists have used a conductive plastic material called polyvinylamide to develop 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 can fit the wearer’s chest tightly. In the experiment, the scientists put an “electronic tattoo” on the surface of the wearer’s heart. When the wearer’s heart beats and causes the chest cavity to vibrate, the sensor can generate the wearer’s electrocardiogram and send it to the mobile phone. At present, scientists are working to improve the data collection and storage capabilities of this “electronic tattoo” and how to perform wireless data transmission. Considering that many conductive plastics are harmless to the human body, scientists also plan to develop artificial cochlea and artificial nerve cells that can be implanted into the human body to treat neurological diseases such as hearing loss, epilepsy and Parkinson’s disease.
  I believe that in the future, conductive plastics will find use in more scientific and technological fields.