Electron transfer polymer domain

This reaction profile of the polymer complex has some similarities with the phenomenon of the polyelectrolyte-catalyzed reactions. It has been reported that the reactions between two positively charged species in aqueous solution are drastically accelerated in the presence of polyanionsS2 84 For example, the electron-transfer reaction between [Co(IIIXen)2(Py)Cl]2+ and [Fe(IIXOH2)6]2+ is very slow because the reaction occurs between two cations however, the addition of a small amount of poly(styrenesulfonate) accelerates the reaction by a factor of 103 84). This result is also interpreted as indicating that the two positively charged reactants are both concentrated in the polyanion domain, so that they encounter each other more frequently [Fig. 17(b)]. 

In the catalyst reoxidation step, contrary to the electron-transfer step, the polymer ligand should shrink because of the formation of the Cu(II) complex. Therefore, the polymer chain may partially repeat are expansion and contraction occurring during the catalytic cycle. When one has a view of the polymer-Cu catalyst as a whole, each part of the polymer catalyst domain, which is drifted in solution, is seen to be fluctuating during the catalytic process [Fig. 32(b)]. The fluctuating shape of biopolymers in enzymic reactions has been pointed out, and the dynamically conformational change of a flexible polymer chain is considered to be one of the effects of the polymer catalyst. 

The rate of electron transfer of the polymer-bound Co(III) complex, cis-[Co(en)2 PVP(N3)]2+ (PVP = poly-4-vinylpyridine, en = ethylenediamine) (15), with [Ru (NH ]2 is very sensitive to the type of dissolved innert anions at a given ionic strength73). In the domain, partial dehydration of the pendant Co III) and, probably, [Ru(NH3)6]2+ ions proceeds successively with an increase in the perchlorate ion concentration, leading to enhancement of the rate. The lower activation enthalpy observed in the perchlorate solution, relative to the chloride ion solution, is attributable to the rate enhancement in the former solution. 

Enhanced electron transfer quenching has also been observed in copolymers containing both ionic and hydrophobic segments [153], probably as a consequence of static quenching from preferential binding of the redox participants in electrostatically favorable regions of the polymeric aggregate. The hydrophobic domains in such polymers act as traps for hydrophobic quenchers, while the hydrophilic interactions enhance dispersion and solubility [154],... 

During the collision of two polymer grains areas with a size of a few square micrometers come into contact. In the contact zone an electron transfer can take place as described in [2] (Fig. 2a). In case of the collision of two chemically different polymer particles one of them preferably interacts as electron pair donator and the other species as electron pair acceptor. In this way laterally expanded charge domains can be formed (Fig. 2b). The low electrical conductivity of the polymer bulk and surface prevents a rapid charge dissipation, hence the formed domain structure seems to be permanently stable. 

The formation of charge domains showed that the fundamental electron transfer process involves a high number of surface sites. The tribo-electric charging of polymers has to be considered as a collective phenomenon. 

Fig. 2 Model concept of the contact charging of polymer grains, a Contact between an electron pair donator domain (empty dots) of the particle 1 and an electron pair acceptor domain (grey dots) of the particle 2. Charge transfers (e-) are taking place. After separation the two particles (b), a positively charged ( ) and a negative charged ( ) domain, remain on the particles surface...

The tribo-electric charging of polymers is a collective phenomenon of numerous electron transfer processes in the contact zone of two colliding particles. The SPM technique allows to visualize the charge distribution on polymer surfaces. It was shown that oppositely charge domains can stably exist side by side although considerable filed strengths are present. 

Interfacial electron-transfer reactions between polymer-bonded metal complexes and the substrates in solution phase were studied to show colloid aspects of polymer catalysis. A polymer-bonded metal complex often shows a specifically catalytic behavior, because the electron-transfer reactivity is strongly affected by the pol)rmer matrix that surrounds the complex. The electron-transfer reaction of the amphiphilic block copol)rmer-bonded Cu(II) complex with Fe(II)(phenanthroline)3 proceeded due to a favorable entropic contribution, which indicated hydrophobic environmental effect of the copolymer. An electrochemical study of the electron-transfer reaction between a poly(xylylviologen) coated electrode and Fe(III) ion gave the diffusion constants of mass-transfer and electron-exchange and the rate constant of electron-transfer in the macromolecular domain. 

It is expected that the electron-transfer reactivity in a macromolecular domain is strongly influenced by the primary structure of polymer matrices, distribution of redox sites, charge density and polarity of polymer domain, etc. In order to assess these factors, the electron-transfer reaction of poly(xylyl-viologen) (5) with Fe(III) ion was selected for investigation. 

The mass-transfer and electron-transfer in the polymer domain is shown as a function of the thickness of the coated pol)rmer film in Figure 6. The currents i and 2 at infinite rotation were calculated by using Routecky-Levich equation (1 ) they represent the mass-transfer and electron-transfer in the pol)rmer domain. The i infinite value decreases with the film thickness, which means that contribution of the mass-transfer process to the redox reaction decreases with the film thickness. 

On the other hand, the 2 infinite value increases with the film thickness, which reflects an expansion of the macromolecular domain, i.e. increase of the redox sites. At intermediate thickness of the polymer layer, the electron-transfer reaction proceeds most rapidly. Further increase of the thickness brings about the steep decrease in the reaction rate via the electron-transfer process, probably caused by the decrease in the electron-transfer efficiency. 

Diffusion coefficient of the substrate (Dg) and diffusion coefficient of the electron-exchange (D ) were calculated from cyclic and disk current voltammograms by using the Koutecky-Levich equation and Fick s first law (14, 15) (Table II). Dg in the polymer domains was estimated as 10 - 10 cm /sec, much smaller than in solution (10 cm /sec). Dg is affected by charge density of the polymer domain, e.g., the diffusion of cations is suppressed in the positively charged domain composed of cationic polyelectrolyte, while anions moves faster. A larger Dg value was observed, of course, for the porous film and not for the film with high density. On the other hand, Dg in the polymer domain was also very small, i.e. 10" - 10" cm /sec. This may be explained as follows. An electron-transfer reaction always alters the... 

Polymer Domain Domain Substrate Mass-transfer Electron- transfer... 

These results suggest some factors for the preparation of electrodes with electron-transfer ability, (i) There is an optimum thickness of the coated polymer film for the electron-transfer reaction, (ii) The polymer matrix should be flexible. Otherwise, the matrix retards the diffusion of a counter ion and suppresses the effective collision between redox sites. (iii) A hydrophilic but uncharged polymer domain is suitable for the mass-transfer process in catalysis. A series of polymer complex coated electrodes were prepared as interfacial catalysts (16), one example is given below. 

Because polymer ligands consist of hydrophobic and hydrophilic sites, a particular domain can form around a metal ion depending on the solvent nature, thereby causing acceleration of electron transfer from substrate to the copper ion. 

Fullerene, Ceo, is quite an effective dopant. It is an excellent electron acceptor, capable of accepting up to six electrons. Photoinduced electron transfer from conducting polymers such as poly(3-octylthiophene), P30T, and poly[2-methoxy-5-(2 -ethylhexyloxy)-p-phenylene vinylene], MEH-PPV, to fullerene Ceo occurs on a timescale of less than 1 ps. A Ceo content of a few percent is sufficient to enhance 0CC in tbc ps time domain by more than an order of magnitude [56]. 

Physico-chemical properties of the microdomain of polymer complexes have been studied by means of Ih-NMR I, light scattering , or fluorescence polarization. Here, the authors tried to evtiluate the microdomain of polymer complexes by the electrochemical cissay. The formation of polyion complex affected the redox behavior of poly-(viologen)s considerably. Fig. 1 shows the cyclic voltammograms for PXV-PSS complex coated electrode. The first redox peak shifted to positive side, and peak broadening was observed by the complex formation. It is clear that the redox behavior was restricted by the complexation. It is known that the electron transfer process must accompany the migration of counter ions to maintain electroneutrality. As in polymer complex microdomain, polyelectrolyte chains interacted with each other and decreased their free volume, they should thereby provide the domain with smaller porosity. 

Yoshino, Zakhidov and co-workers [175,176] reported that doping the conjugated polymer/C o composites with alkali atoms results in granular superconductivity of the Cfio component embedded in the polymer matrix. Photoinduced electron transfer may increase the number of superconducting domains in these composites. 

---