Maya Ellison
For a long time, it was commonly understood that plastics do not conduct electricity—unlike metals, which are good conductors. However, this notion has been challenged by scientists who have discovered that plastics can, in fact, conduct electricity under certain circumstances. This discovery led to a Nobel Prize in Chemistry in 2000 for chemist Alan MacDiarmid and his colleagues. So, how does this work?
| Characteristics | Values |
|---|---|
| Conductivity | Poor conductor of electricity, but can conduct under certain circumstances |
| Composition | Comprised of lengthy chains of carbon and hydrogen atoms |
| Free electrons | Few or no free electrons |
| Reaction | Non-reactive |
| State | Likely to melt under high current |
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What You'll Learn
Plastic's use in electrical insulation
Plastics are generally considered good electrical insulators with high dielectric strength properties and excellent fire resistance. They are therefore used in a variety of applications where their insulating properties are needed. For example, PVC is widely used to insulate electric wiring, while thermosets, which can withstand high temperatures, are used for switches, light fittings, and handles.
Plastics are especially useful for electrical insulation in housings for goods such as hairdryers, electric razors, and food mixers. This is because they protect the consumer from the risk of electric shock. They are also used for cool-touch toasters, deep-fat fryers, and kettles to reduce the risk of burns.
The design freedom granted by plastics has contributed to the stylish appearance of modern appliances such as VCRs, CD players, DVD systems, personal computers, and TV sets. They are also used to make hygienic and attractive knobs, handles, and door facings on cookers, as well as liners, handles, and internal fittings for refrigerators and freezers.
In addition to their insulating properties, plastics offer several other advantages. They are lightweight, reducing the weight of tools and equipment, which in turn lowers electricity consumption. They can be designed to have any colour or texture, making them suitable for ergonomic curves that enhance the safety and ease of use of modern tools. Plastics are also durable, hygienic, and easy to clean and maintain. They do not corrode like metals or rot like other organic materials, and they are resistant to oil and acid.
It is important to note that while plastics are typically considered insulators, they can conduct electricity under certain circumstances. For example, by adding iodine to the polymer, the conductivity of the plastic can be increased. This discovery was made by chemist Alan MacDiarmid and his colleagues, who were awarded the Nobel Prize in Chemistry in 2000.
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Plastic's ability to conduct electricity under certain conditions
For a long time, it was commonly understood that plastics do not conduct electricity. However, this notion has been challenged by scientists who discovered that plastics can, in fact, conduct electricity under certain conditions.
Plastics are typically considered poor electrical conductors due to their lack of free electrons, which are necessary for conducting electricity. This is because the molecules in plastics are composed of long chains of carbon and hydrogen atoms. As a result, plastics are used as insulators on wires and in other applications where electrical insulation is required. For instance, the plastic used in sandwich bags does not have the density to withstand the electric current produced by a lighter, and the current will burn through the plastic.
However, it is important to recognize that the conductive properties of plastics can be altered under certain circumstances. Notably, in 2000, chemist Alan MacDiarmid, along with his colleagues, discovered that adding iodine to the polymer could increase the conductivity of plastics. Iodine, being a strong oxidant, attracts the electrons in the polymer, leading to a less dense arrangement of electric charge carriers, which then become more agile and can flow, similar to what is observed in metals. This discovery earned them the Nobel Prize in Chemistry.
Polyacetylene (PAC), a plastic commonly used for electrical insulation, was the first plastic to gain recognition as a conductor of electricity due to the addition of oxidants. While the initial conductivity level was very good, it was found to be significantly reduced due to the oxidants' reactivity with atmospheric oxygen. Nonetheless, this discovery highlights the potential for enhancing the conductivity of plastics through specific modifications, thereby challenging the traditional view of plastics as solely insulators of electricity.
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The discovery of conductive polymers
For a long time, polymers were considered to be insulating materials. However, in the early 1970s, this notion changed when Japanese chemist Hideki Shirakawa accidentally synthesised polyacetylene (PAC)—a plastic used for electrical insulation—in his laboratory in Tokyo.
In 1977, Shirakawa, along with his colleagues Alan J. Heeger and Alan MacDiarmid, reported high conductivity in oxidised iodine-doped polyacetylene. This discovery led to the trio being awarded the 2000 Nobel Prize in Chemistry "for the discovery and development of conductive polymers".
Polyacetylene did not find practical applications, but it did draw the attention of scientists and encouraged the rapid growth of the field. Since the late 1980s, organic light-emitting diodes (OLEDs) have emerged as an important application of conducting polymers. Linear-backbone "polymer blacks" (polyacetylene, polypyrrole, polyindole, and polyaniline) and their copolymers are the main class of conductive polymers.
Conductive polymers are organic polymers that can have metallic conductivity or exhibit semiconductor behaviour. They are easy to process, mainly by dispersion, and have tuneable conductivity along with flexibility. These unique properties make conductive polymers potential candidates in various biomedical applications. Over the last decade, multidimensional conductive polymers with diverse morphologies and structures have been fabricated, such as spheres, particles, fibres, and hollow-type structure tubes.
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The impact of electron density on conductivity
For a long time, it was commonly understood that plastics do not conduct electricity, unlike metals. However, this understanding has evolved, and it is now recognized that plastics can conduct electricity under certain circumstances.
The ability of a material to conduct electricity is influenced by various factors, including electron density. Electron density, also known as conduction electron density, refers to the number of conduction electrons in a given material. Conduction electrons are those that are free to move within the material's structure, contributing to its electrical conductivity. In metals, for example, the atoms lose their valence electrons, creating a lattice of positive ions (cations) and delocalized conduction electrons that can move between these ions, facilitating electrical conduction.
In the case of plastics, the impact of electron density on conductivity is more complex. Pure, unmodified plastics typically have low electron densities and are considered insulators. However, through modifications such as the addition of certain chemicals or dopants, the electron density and conductivity of plastics can be altered. For example, the addition of iodine, a strong oxidant, to a plastic polymer can increase its conductivity by attracting electrons and reducing their density. This modification enhances the mobility of the electric charge carriers, allowing them to flow more easily, similar to the behavior of electrons in metals.
While electron density is a critical factor in determining the conductivity of a material, it is important to consider the broader context of electron behavior and the specific characteristics of the material in question. The interplay between electron density, mobility, and interactions with other particles contributes to the overall conductivity, and these factors can vary between different materials and conditions.
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The effect of oxidants on plastic's conductivity
Plastics are bad conductors of electricity, but under certain circumstances, they can conduct electricity. The journey into conductive plastics began in the 1970s with the accidental discovery of polyacetylene by Shirakawa, a Japanese chemist. This breakthrough opened the door to a whole new world of conductive properties.
Oxidants play a crucial role in the creation of conductive plastics. They help form a conductive network within the polymer matrix, and by adjusting the level of oxidation, the electrical resistivity of these materials can be altered, providing flexibility for various applications. When oxidants like iodine are added to the polymer, the number of charge carriers increases, and the polymer's electronic structure changes. This results in a less dense packing of electric charge carriers, making them more agile and able to flow more freely, similar to metals.
The addition of dopants, such as iodine, enhances the flow of electrons within the polymer, creating charge carriers that enable the smooth movement of electricity. This process can significantly increase the polymer's conductivity, almost matching the conductivity of metals like copper.
However, the conductivity of these doped polymers can decrease over time due to reactions with atmospheric oxygen, which can lead to degradation. This process, known as photo-oxidation or oxidative photodegradation, is the most significant factor in the weathering of plastics, causing the polymer chains to break and the material to become brittle and mechanically fail.
While photo-oxidation can be detrimental to the stability of plastics, it has potential benefits for recycling. For example, Clarke and coworkers used Ag-based photothermal nanoparticles (AgNPs) to degrade low-density polyethylene (LDPE) photothermally. Additionally, biodegradable additives, such as OXO-biodegradation additives (transition metal salts like iron, manganese, and cobalt), can be used to accelerate the degradation of single-use plastics.
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Frequently asked questions
Plastics are poor conductors of electricity because they have few or no free electrons. However, under certain circumstances, plastics can conduct electricity. For example, by adding iodine to the polymer, the conductivity of the plastic can be increased.
Plastics are made up of molecules that are formed of lengthy chains of carbon and hydrogen atoms.
Polyacetylene (PAC) is a plastic that can conduct electricity.
