Composite conductive polymer material nano silver coated copper powder (minimum 2um)

Conductive polymer materials are polymer materials with conjugated main electron systems in the main chain, which can be doped to achieve a conductive state with a conductivity of over 1000S/cm. After 40 years of development, people have conducted in-depth research on the types and mechanisms of conductive polymers, as well as how to improve their conductivity. Various explorations have been made on the synthesis and application of conductive polymers. Due to its unique properties, conductive polymers are not only widely used as conductive materials, but also have potential application value in fields such as energy, optoelectronic devices, sensors, and molecular wires.

The Conductive Mechanism of Conductive Polymer Materials

1Composite conductive polymer material

The dispersion state of fillers in composite conductive polymer materials determines the conductivity of the material. From the percolation theory, it can be seen that when isolated and dispersed filler particles are loosely filled in the material, a continuous conductive path may be formed when the volume dispersion reaches a certain critical content. At this point, ions are in two states: one is that charge carriers can flow continuously inside the conductor, and physical contact occurs between ions; Secondly, due to the presence of a thin layer of adhesive between ions, the carriers themselves are activated and move. So, the condition for composite conductive polymer materials to conduct electricity is that the filling material should be dispersed to a certain extent and form a loose network distribution.

The composition of the filler material, the dispersion state of the filler particles, and their interaction with the polymer matrix in composite conductive polymer materials all determine the conductivity of the composite material. In order for the material to have better conductivity, it is necessary to ensure that the filler particles can be well dispersed and form a three-dimensional network structure or honeycomb structure.

IIStructural conductive polymer materials

In ionic conductive polymer materials, large molecular chains such as polyether and polyester form a helical spatial structure, and cations coordinate and complex with them. Under the promotion of the movement of large molecular chain segments, cations migrate through vacancies in their helical channels, or cations and anions dissolved by large molecules undergo transition diffusion between the gaps of the large molecular chain.

In electronic conductive polymer materials, most of the main polymer is a conjugated system, and the π - bonds in the long chain have high electron activity, especially after forming charge transfer complexes with dopants, they are easily released from the orbitals to form free electrons.

The π electrons within and between polymer chains can form conduction bands due to orbital overlap, providing channels for the transfer and transition of charge carriers. Under the influence of external energy and the vibration of the polymer chain, current can be conducted.

Classification of Conductive Polymer Materials

Conductive polymer materials can be divided into two categories: composite materials and structural materials based on their production methods and structures. Although these two types of materials have similar characteristics, they also have significant differences, and their application directions and ranges are also different.

1Composite conductive polymer material

It is made by filling composite, surface composite or layered composite of general polymer materials and various conductive substances. The main varieties include conductive plastics, conductive rubber, conductive fiber fabrics, conductive coatings, conductive adhesives, and transparent conductive films. Its performance is closely related to the type, dosage, particle size, and state of conductive fillers, as well as their dispersion state in polymer materials. Common conductive fillers include carbon black, metal powder, metal foil, metal fiber, carbon fiber, etc.

IIStructural conductive polymer materials

It refers to polymer materials that have conductive properties either by themselves or after doping. According to the conductivity, it can be divided into polymer semiconductors, polymer metals, and polymer superconductors. According to the conductive mechanism, it can be divided into electronic conductive polymer materials and ion conductive polymer materials.

The structural characteristics of electronic conductive polymer materials are the presence of linear or planar conjugated systems, which conduct electricity through the activation of conjugated π electrons under the action of heat or light. The conductivity is generally in the range of semiconductors. The use of doping technology can greatly improve the conductivity of such materials. If a small amount of iodine is doped into polyacetylene, the conductivity can be increased by 12 orders of magnitude, making it a "polymer metal". Doped polysulfide can be transformed into polymer superconductors at ultra-low temperatures.

Structural conductive polymer materials are used for the trial production of lightweight plastic batteries, solar cells, sensor devices, microwave absorbing materials, and semiconductor components. However, currently these materials have not yet entered the practical stage due to poor stability (especially the poor oxidation stability of doped materials in air) and issues with processing formability and mechanical properties.

Synthesis of Conductive Polymers

Conductive polymer materials are emerging materials that have only been developed in the past two to three decades. In 1975, L.F. Nichols et al. synthesized polysulfide nitrogen (SN) x in the laboratory, which has superconductivity at low temperatures and conductivity comparable to silver, breaking the constraint that polymer is an insulator. Two years later, Professor Shirakawa from Tsukuba University in Japan discovered that doped polyacetylene (PA) exhibited metallic properties, thus giving birth to a new interdisciplinary field - conductive polymer science. Conductive polymer materials have achieved the transformation from insulators to semiconductors, and then to conductors, making them the material with the largest morphological leap among all materials, and unparalleled by any material so far. Its unique structure, excellent physical and chemical properties have attracted widespread attention in the academic community and have been widely applied in various fields. Electrolytic capacitors are an important example. At present, the widely used aluminum electrolytic capacitors use liquid electrolytes. Although these capacitors have the characteristics of large capacity, small size, and low price, their performance is limited due to the use of liquid electrolytes. Tantalum electrolytic capacitors have certain improvements compared to aluminum electrolytic capacitors.

Aluminum electrolytic capacitors cannot use the thermal decomposition method of manganese nitrate to prepare solid electrolyte MnO2 like tantalum electrolytic capacitors, and conductive polymer materials have become the preferred material for preparing solid electrolytes for aluminum capacitors. In 1983, Sanyo Electric of Japan developed an aluminum electrolytic capacitor (OS-CON) using organic semiconductor TCNQ complex salt material as the electrolyte. In April 1989, Japan developed a stacked aluminum electrolytic capacitor (SP-CON) using conductive polymer material polypyrrole (PPY) as the electrolyte. After 1996, wound aluminum electrolytic capacitors using polyethylene dioxythiophene (PEDT) as the working electrolyte appeared again. At present, the applications of polyaniline and polypyrrole in solid electrolyte capacitors have been reported. Here, we mainly introduce the synthesis methods of polyaniline and polypyrrole.

1Synthesis of Polyaniline

Among conductive polymer materials, polyaniline (PAn), as one of the most likely conductive polymer materials to be applied in practice, has the advantages of inexpensive monomers and simple polymerization methods. Conductive polyaniline has excellent electrochemical properties, good chemical stability, and high conductivity. At room temperature, polyaniline is a typical semiconductor material with a conductivity of 10-10S/cm. After doping, the conductivity of polyaniline can reach 5S/cm, and the conductivity can be adjusted between 10-10S/cm and 100S/cm. Its color can change with the electrode potential and the pH value of the solution, and it has good electrochemical reactivity. It is a new type of electrode active material and has become a hot topic in the research of conductive polymer materials. Previous solid electrolyte capacitors used porous metals such as tantalum and niobium as anodes, forming oxide films on the metal as dielectric layers, and manganese dioxide as cathodes. Recently, there have been numerous reports of using polymers as cathodes. The synthesis of polyaniline can be achieved through chemical and electrochemical methods. With changes in polymerization methods, solution composition, and reaction conditions, the resulting polyaniline exhibits significant differences in composition, structure, and properties. In the process of making electrolytic capacitors, the choice between chemical or electrochemical methods varies depending on the substrate. For the synthesis of polyaniline on the anode of capacitors, chemical methods require oxidants, but the reaction can be carried out at room temperature, making it easier to achieve; Electrochemical method does not require oxidants, and the polymerization reaction occurs on the electrode, but electrochemical polymerization makes the coating not necessarily uniform. If the resistance of the base film is higher than 1.5 Ω/cm2, electrochemical method cannot be used, only chemical oxidation method can be selected; If the resistance of the base film is less than 1.5 Ω/cm2, both chemical and electrochemical methods can be used.

IIChemical synthesis of polyanilineoxidation polymerization

The synthesis of polyaniline by chemical oxidation method involves the oxidative polymerization of aniline under appropriate conditions using an oxidant. This is a widely used method in the production of capacitors. The chemical oxidative polymerization of aniline is usually carried out in an aniline/oxidant/acid/water system. The general method is to mix aniline and acid in a certain proportion evenly in a glass container, then use an ice water bath to lower the system temperature to 0 ℃~25 ℃. Under stirring, the oxidant is added dropwise, and the addition is completed within 3 minutes. The color of the system changes from light to dark, continue stirring for 90 minutes, then filter and wash until the filtrate is colorless, obtaining dark green polyaniline powder.

Common oxidants include ammonium persulfate (NH4) 2S2O8), potassium dichromate (K2Cr2O7), hydrogen peroxide (H2O2), and potassium iodate (KIO3). Ammonium persulfate is widely used due to its absence of metal ions and strong oxidizing ability. The recently reported application of manganese dioxide (due to its wide source, low price, non toxicity, high safety, and easy manufacturing) as an oxidant, using hydrochloric acid as a medium, successfully synthesized conductive polyaniline by chemical oxidation method. Meanwhile, the structure and conductivity of the obtained polyaniline are similar to those of ammonium persulfate (APS) as an oxidant.

According to Table 1, under the same conditions, the conversion rate of polyaniline synthesized using APS as the oxidant is equivalent to that using MnO2 as the oxidant, and the conductivity of APS as the oxidant is higher than that of MnO2 as the oxidant. Despite differences in conductivity, MnO2 remains an optional oxidant for aniline polymerization.