Conductive textiles polymer substrates

The in situ polymerization of aniline to form an electrically conductive textile was also first reported by Kuhn and coworkers [78,79] in which the polyaniline was deposited onto a textile substrate from an aqueous solution containing aniline, ammonium persulfate, hydrochloric acid, and either the disodium salt of 2,6-naphthalenedisulfonic acid or 1,3-benzenedisulfonic acid. In these studies, the polymerization conditions were controlled in order to deposit the polyaniline layer only onto the textile support with no polymer precipitating in the bulk liquid phase. This was accomplished by using dilute solutions of aniline (0.03 M). A subsequent study by Tzou and Gregory [92] on the deposition of polyaniline to nylon-6 fibers was focused on investigating the reaction kinetics of the chemically oxidative polymerization of aniline... 

Many applications of conducting textiles involve the formation of laminates or composites with various thermoset resins such as epoxy, imide, and rubber. The adhesion between the various layers of the composite is a critical factor in the utility of these structures. Only a few papers have addressed the adhesion of polypyrrole-coated fabrics with epoxy resins [44,451. The adhesion at the polypyrrole/textile interface is reasonably strong because of the intermolecular forces between the adsorbed polymer layer and the substrate. The adhesion at the polypyrrole/epoxy interface benefits from the po-... 

Treated conductive fibers can be produced by the combination of two or more materials, such as non-conductive and conductive materials. This conductive textiles can be produced in various ways, such as by impregnating textile substrates with conductive carbon or metal powders, patterned printing, and so forth. Conducting polymers, such... 

Polyanilines (Scheme 36) are conjugated polymers whose it electrons are delocalized over the whole molecule. They are important conducting polymers that also act as semiconductors, in a similar manner to inorganic semiconductors121 m. They are made by chemical or electrochemical (anodic) oxidation of aniline. The product, a poor textile colorant, dates from the 1860s, and is still known by the name given at that time, emeraldine. In the electrochemical process, it is possible to produce thin films directly on conductive substrates. Polyanilines have been used in photoelectrochemical devices124-126. 

The ITO free hole collecting layer was realized using highly conductive solution of PEDOT PSS as a polymer anode that is more convenient for textile substrates in terms of flexibility, material cost, and fabrication processes compared with ITO material. Based on procedure described in reference 25 a sophisticated and simple design was presented to show how thin and flexible could be a solar cell panel. 

Another way to obtain a flexible textile compatible strain sensor is based on conductive polymer composites (Cochrane et al., 2007). Carbon black nanoparticles are captured in a thermoplastic elastomer matrix that can be printed onto a textile substrate (Fig. 2.4). Upon strain deformation, the distance between the particles will change and an electrical current will pass less easily through the composite, resulting in a resistance change. 

Thermal conductivity can be defined as a measure of the rate at which heat is transferred through the unit area of the fabric across the unit thickness under a specified temperature gradient. The thermal conductivity coefficient of some fibers/polymers, air, and water is compared in Table 19.1 in order to understand the impact of the material on thermal properties of textile substrate (Table 19.1) [25]. 

The second way to enhance the usability of ICPs is to apply coatings thereof on textile materials. A very thin layer of conductive polymers can be applied on the surface of textile substrates by solution casting, inkjet printing, in situ polymerization, vapor phase polymerization, and chemical vapor deposition techniques [26—29]. The nano-microscale conductive coatings not only provide high level of conductivity but also preserve the flexibility and elasticity of substrate fibers. However, due to the health-related issues of some carbon-based materials one has to be observant about what is possible and what is not in apparel applications. 

In our lab we transformed the conventional textiles into electrically conductive materials by applying very thin layers of conjugated polymer. For this purpose, an efficient coating technique called chemical vapor deposition (CVD) was used to coat the textile substrates with conjugated polymer, poly(3,4-ethylenedioxythiophene) (PEDOT), in the presence of a suitable oxidant. A schematic diagram of all steps involved in this coating process is shown in Fig. 28.8. 

Another widely used approach is the in situ polymerization of an intractable polymer such as polypyrrole onto a polymer matrix with some degree of processibil-ity. Bjorklund [30] reported the formation of polypyrrole on methylcellulose and studied the kinetics of the in situ polymerization. Likewise, Gregory et al. [31] reported that conductive fabrics can be prepared by the in situ polymerization of either pyrrole or aniline onto textile substrates. The fabrics obtained by this process maintain the mechanical properties of the substrate and have reasonable surface conductivities. In situ polymerization of acetylene within swollen matrices such as polyethylene, polybutadiene, block copolymers of styrene and diene, and ethylene-propylene-diene terpolymers have also been investigated [32,33]. For example, when a stretched polyacetylene-polybutadiene composite prepared by this approach was iodine-doped, it had a conductivity of around 575 S/cm and excellent environmental stability due to the encapsulation of the ICP [34]. Likewise, composites of polypyrrole and polythiophene prepared by in situ polymerization in matrices such as poly(vinyl chloride), poly(vinyl alcohol), poly(vinylidine chloride-( o-trifluoroethylene), and brominated poly(vi-nyl carbazole) have also been reported. The conductivity of these composites can reach up to 60 S/cm when they are doped with appropriate species [10]. 

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. 

Although in this work microfibers textile, not nanofiber, was used as the substrate, we consider that instead of mlcrofibers, CNFs and conductive polymer nanofibers can also be used as the electrode substrate which will even increase the conductivity. Wei and co-workers have successfully obtained graphene nanosheets (GNS) incorporated with RUO2 and Ti02 nanoparticles (Fig. 7.7). If these composite graphene nanosheets coated on porous nanofibers, excellent supercapacitor electrode can be expected. 

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