Text/Meteor Polymer NOVA
For many applications in electronics, inherently good insulating properties of polymeric materials are a basic requirement. However, some areas require polymeric materials with improved conductivity, such as preventing electrostatic loading, forming electrostatic shielding of plastic packages, making electrodes, LEDs, FETs, etc. Conductive thermoplastic compounds can be made by adding conductive fillers or reinforcing materials. Next, we introduce conductive polymers.
Chemical structure. Intrinsic conductive polymers (ICPs) have been focus of research for many years and their use is growing. These organic materials are composed of conjugated double bonds (alternating single or double bonds), which is beautifully demonstrated in polyacetylene. Adding electron donors (Na, K, Cs) or electron acceptors (J2, SbCl5, FeCl3, etc.), atoms or molecules that release electrons (reduction) or accept electrons (oxidation), which leads to an increase in electron mobility, conductivity. The speed can reach 105S/cm. Like metals, individual free electrons remain, no longer associated with other atoms, but sliding and transferring charge along molecule. This process in semiconductor technology is called doping.
The following formula illustrates this for polyethylene blocks, PACs (polyamide hydrocarbons).
The figure below provides an overview of conductivity achieved by doping.
Electroluminescence is defined as ability of certain materials to emit light when an electrical voltage is applied, which led to development of OLEDs (Organic Light Emitting Diodes). They consist of a sheet of quartz or glass, which in simplest case has three layers: indium tin oxide as a positive electrode, a thin film of light-emitting polymer [poly(3,4-ethylenedioxythiophene)], and finally an A layer of calcium, magnesium or aluminum acts as a cathode. The first generation conductive polymers were completely insoluble and did not melt. Soluble conductive polymers have been developed for casting thin-layer conductive polymers onto tape: second generation polymers such as polystyrene and vinylene based polymers. Three-dimensional soft transparent electroluminescent systems (TOLED: Transparent Organic Light Emitting Device) are currently available as options, consisting of multilayer thin films. The conductive polymer can be applied by spinning, dipping, spraying or vacuum deposition onto a carrier film with a thickness of 0.15-0.8 mm. When an alternating current is connected to electrodes, middle layer will emit light. This feature is called “smart surface technology”, which consumes almost no energy and generates no heat. Luminous plastic parts can be used in car interior decoration and console lighting, positioning and security signals, folding monitors. OLEDs are used in temperatures ranging from -4 to 70°C, and due to their chemical variability, they can be made in any color, including white. In light absorption state, photoexcited light can be generated by separation of double bonds, and when double bonds are reconnected, bond free energy can be emitted as light. Masterbatches based on polyethylene, polypropylene, polyamide, polystyrene and other engineering plastics are also available.
Performance. Polyacetylene (PAC) is available as a powder, adhesive or film (also transparent, oriented up to 600% and able to have highest conductivity > 105 S/cm). They are insoluble and their electrical conductivity is 10-5~105 S/cm depending on polymerization process. Before alloying, density range is 0.4~0.9g/cm3, after alloying 1.12~1.23g/cm3.
The thermal stability of undoped polyphenylene polymer reaches about 450℃. For example, by doping anode with FeCl3, a conductivity of about 102 S/cm can be obtained. This product is sensitive to hydrolysis. Polymers doped with potassium with a cathode are also sensitive to oxygen.
Polyparaphenylene vinylene (PPV) and polyparaphenylene (PPV) are used in planar light emitting diodes and electron luminescence.
Polyheteroaromatic, polypyrrole (PPY), polyfuran (PFU), polythiophene (PT) These materials can undergo electrochemical polymerization and be removed from anode as a thin film. Thickness of self-retaining plateThe value starts from about 30 µm, Xu layer thickness is 0.01 µm, electrical conductivity is 10-4~102 S/cm, tensile strength is 20~80 MPa, and elongation at break is 10%~20%. . Application examples: antistatic equipment (BP film), heating tape, fuses, sensors, batteries. When doped with aqueous solutions of various acids, polyaniline (PANI) can reach a conductivity of about 10 S/cm. Polyaniline is an insoluble and infusible polymer. Being fine mixtures (nanopowders) in paints, they modify corrosion potential of iron, steel, aluminium, zinc, stainless steel and copper, coating these metals with parylene lightens these precious metals and thus reduces corrosion process, especially minimal damage. Other applications are solar cells, gas separation membranes, fuel cells, batteries, sensors. Polyethylenedioxythiophene (PEDT) polymerizes in solution to a non-flammable, non-flammable powder with a powder conductivity of 30 S/cm. On PC or glass, surface resistance is σe≈10002 Ohm/cm2 at a thickness of about 0.1 mm. Applied to conductive coatings on solid electrolytic capacitors, plastics or glass (for example, by oxidative polymerization with a solution of ferric tosylate in n-butyl alcohol).
Polyethylenedioxythiophene polystyrenesulfonate (PEDT/PSS). As a result of oxidative polymerization of PEDT monomer polymer in an aqueous solution of polysulfonic acid, PEDT colloidal solutions suitable for processing are formed. Potassium peroxodisulfate can be used as an oxidizing agent. Minimum surface resistance σe≈150 Ohm/cm2. Used in films, antistatic coatings, glass, LEDs, OLEDs.