Polyaniline mechanical strength

The contraction ratio of polyaniline film as a function of strain obtained in the stretched polyaniline film is shown in Figure 8.11 [25]. The result indicates that the contraction force is of the order of 1-2 MPa, which is about 10 times larger than that of natural muscles. Under smaller strains, the contraction ratio for the perpendicnlar direction is slightly larger than that observed in the stretched direction. At larger strains, however, the contraction ratio decreases more rapidly in the stretched direction than in the perpendicular direction, indicating that the mechanical strength is weaker in the direction perpendicular to polymer chains. 

The formation of macrovoids in these asymmetric polyaniline hollow fibers is undesirable as they weaken the mechanical strength and may lead to defects in the selective layer, which make them nonviable for many separations applications. The formation of macrovoids in hollow fiber membranes is generally caused by fast precipitation kinetics of the polymer solution in the coagulation bath. The formation of macrovoids when spinning polyaniline hollow fibers was foimd to be highly dependent on... 

However, the production of all-organic fibers from ICPs is still complicated and expensive. Several attempts have been made to obtain conductive fibers from ICPs such as polyaniline, PEDOT PSS, and pure PEDOT with conductivity values from 150 to 250 S/cm [22,23]. However, due to poor mechanical strength, microscale size, a low production rate, brittleness, and difficult processing, useful commercial applications are stiU limited. On the other hand, combination of other textile materials with ICPs could enhance their application areas. It could be done in two ways, either by mixing ICPs with insulating polymers such as polypropylene, polyethylene, and polystyrene, or by coating conventional textiles with ICPs. The coating method is explained in the next section. 

Coatings of fabrics is important as it provides flexibility and mechanical strength to the otherwise powdery, unprocessable poly aniline. Undoubtedly, the in-situ grafting of conducting polyaniline onto substrates can be compared with coating of the electrode during polymerization as both these are solid-liquid interfacial reactions, and therefore the mechanism for the formation of polyaniline cannot differ drastically [302-5]. The polymerization reactions mechanism can be written as... 

With few exceptions, the mechanical properties of conductive polymers are rather poor. This is a result of the cross-linked nature and aromatic character of the backbone. One exception is polyaniline, which can be prepared as oriented crystalline fibers of excellent strength (see Chapter 18). The use of a textile substrate represents a convenient method of introducing mechanical strength, flexibility, and processibility to conducting polymers for practical applications. 

Since inter-chain interactions are responsible for increasing both conductivity and mechanical properties,, it is not surprising to find that the conductivity and tensile strength of doped polyaniline films are monotonically related,. ... 

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