Electrochemical techniques polymerization

Electrochemical technique (also electrocoagulation) is a simple and efficient method for the treatment of drinkable water. Recent results reported by Part-hasarathy and Yang [54,55] have demonstrated that electrocoagulation (EC) using aluminium anodes is effective in defluoridation. In the EC cell, the aluminium electrodes sacrifice themselves to form aluminium ions first. Afterwards the aluminium ions are transformed into AI(OH)3 before being polymerized to Aln(OH)3n. The AI(OH)3 floe is believed to adsorb F strongly as illustrated by the equation. 

PAn s are most commonly prepared through the chemical or electrochemical oxidative polymerization of the respective aniline monomers in acidic solution. However, a range of polymerization techniques has now been developed, including... 

It is the aim of this chapter to give an overview on both chemical and electrochemical techniques for producing metallic-particle-based CP nanocomposite materials and to outline the progress made in this field. The various synthetic approaches are organized in such a way as to present first those involving metal particle deposition in the course of polymerization, and subsequently post-polymerisation procedures that involve chemical, electrochemical, or adsorption processes (Figure 7.1). Well-established approaches, along with some newly developed techniques will be discussed, with special emphasis on those that are still underdeveloped. Synthesis of metal oxide particle-based CP composites (see e.g. [8]), as well as modification of CPs with transition-metal complexes (see e.g. [5]) remain outside the scope of this chapter. 

Among the conjugated polymers, polypyrrole (PPy) is the most representative one for its easy polymerization and wide application in gas sensors, electrochromic devices and batteries. Polypyrrole can be produced in the form of powders, coatings, or films. It is intrinsically conductive, stable and can be quite easily produced also continuously. The preparation of polypyrrole by oxidation of pyrrole dates back to 1888 and by electrochemical polymerization to 1957. However, this organic p>-system attracted general interest and was foimd to be electrically conductive in 1963. Polypyrrole has a high mechanical and chemical stability and can be produced continuously as flexible film (thickness 80 mm trade name Lutamer, BASF) by electrochemical techniques. Conductive polypyrrole films are obtained directly by anodic polymerization of pyrrole in aqueous or organic electrolytes. 

In comparison to inorganic counterparts, less number of organic SHSs can be prepared via electrochemical techniques because of the insulating properties of the organic materials. Conducting polymers (CPs) are exceptional and can be easily synthesized by electrochemical polymerization. Scheme 2 shows the structures of several important CPs. 

There are numerous ways of attaching polymers to a solid surface. Examples are photo cross-linking of pre-formed polymer chains, in-situ atom transfer radical polymerization (ATRP), electron beam irradiation,and plasma polymeriza-tion.f Electrochemical techniques are particularly suited for conducting substrates. For example, Palacin et al. have grafted vinylic monomers from anhydrous solutions.f This technique is mainly based on an anionic polymerization and leads to a covalent link between the polymer and the metal. Schuhmann et al. 

Our work employs electrochemically initiated polymerization (EIP) which is an easy and flexible method to produce surface coatings of various kinds. The technique makes use of the decomposition of an electro-active initiator at an electrode to start a free-radical polymerization. The polymer is formed directly at the electrode surface. As a consequence, the films adhere tightly to the surface. Adhesion is based on physisorption of the hydrogel to the metal. Note in this context that EIP is different from electrografting of conductive polymers. In EIP, the initiator is the electro-active species, rather than the monomer. Recently, we reported on the formation of thermoresponsive poly-A -isopropylacrylamide (pNIPAm) hydrogel coatings on gold surfaces based on this approach. ... 

The aim of this book is to present the insights of experts on emerging experimental techniques and theoretical concepts that are or will be in the vanguard of the field of electrochemistry in ionic liquids. The two volumes of this book provides the reader with a broad and self-contained account of electrochemical techniques available to work in ionic liquids. It also gathers and critically discusses the important properties of protic ionic liquids, deep-eutectic solvents, task-specific ionic liquids, polymeric ion gels, and lithium-ion solvation, relevant to electrochemistry. 

Murray and his group showed in 198 that bilayer polymeric films and films sandwiched between two electrodes may be used as diodes or triodes via redox conduction that is potential dependent (126,127). Since then, Wrighton s group has carried this concept into the microscopic realm. As discussed above, microelectronic technology was used to prepare arrays of ultramicroelectrodes. These were modified using electrochemical techniques such as electropolymerization or electrodeposition (120,128,129). 

Table 3 lists some potentials of monomers and polymers. As in the case of PAn the polymers are easier to oxidize — reversibly — than the inserted monomers — irreversibly — (for PAn see Fig. 5), Also, polymers not prepared by an electrochemical technique, e.g. the phthalocyanines 12, polyacetylene and graphite, can be oxidized or reduced reversibly. Not all organic compounds are able to be polymerized by an electrochemical technique on a carrier electrode. In the case of oxidative polymerization the neutral monomers are first oxidized at the anode irreversibly. The cation radicals R" " formed are unstable and rather reactive. A high concentration... 

The definition of a chemically modified electrode (CME) is a conducting or semiconducting material that has been coated with a monomolecular, multi-molecular, ionic, or polymeric film (termed adlayer see Figure 8.1) which alter the electrochemical, optical, and other properties of the interface (1, 2). The conductive and semiconductive substrates are derived from conventional electrode materials (see Chapter 5), while the adlayers are widely diverse in their origins and properties. This diversity extends or enhances the range and scope of electrochemical techniques. 

Pyrrole was first polymerized in 1916 [1,2] by the oxidation of pyrrole with H2O2 to give an amorphous powdery product known as pyrrole black. However, little further interest was shown in this material until it was electrochemically prepared in the form of continuous films. The electrochemical synthesis of polypyrrole dates to the early work of DalTOllio [3], who also obtained pyrrole blacks by electrochemical oxidation of pyrrole in aqueous sulfuric acid on a platinum electrode. In 1979 [4] electrochemical techniques to synthesize polypyrroles become a useful way to obtain highly conductive free-standing materials. Chemical and electrochemical methods of synthesis have since then been improved in order to optimize the physical and chemical properties of those materials. 

Important processing methods Langmuir-Blodgen technique of monolayer production, solution polymerization over the substrate, electrochemical anodic polymerization, chemical oxidation of pyrrole in carbon black suspension... 

Polythiophene and its derivatives can be polymerized by chemical or electrochemical techniques. In this study, the electrochemical method was utilized.The mechanism is a cationic radical polymerization 11). The polymerization pathway can be summarized in the following steps 1) oxidation of the monomer to form a radical cation, 2) dimerization of the radical cations, 3) loss of proton to yield a neutral dimer, 4) oxidation of dimer to form a radical cation, 5) reaction of dimer radical cation with another radical cation, 6) repeat of the this study, are 3-methylthiophene, tetrabutylammonium tetrafluoroborate (TBATFB), as the supporting electrolyte. The organic solvent was acetonitrile. The resulting polymer was the first conducting polymer family found to be stable in air and water in both their doped or undoped state. 

The Kelvin probe technique is a unique reference electrode that allows non-contact measurement of electrode potentials. It can be used for measuring electrode potentials through insulating dielectric media such as air or polymeric films. It is mainly used where standard electrochemical techniques, which require a finite ionic resistance between working and reference electrodes, will fail. 

---