Polyelectrolyte films

In the present work it was studied the dependence of analytical characteristics of the composite SG - polyelectrolyte films obtained by sol-gel technique on the content of non-ionic surfactant in initial sol. Triton X-100 and Tween 20 were examined as surfactants polystyrene sulfonate (PSS), polyvinyl-sulfonic acid (PVSA) or polydimethyl-ammonium chloride (PDMDA) were used as polyelectrolytes. The final films were applied as modificators of glass slides and pyrolytic graphite (PG) electrode surfaces. 

FIG. 7 Confocal laser scanning microscopy image of a fonr-layer polyelectrolyte/CdTe(S) nanocrystal shell assembled on 1.5-p,m-diameter ME particles. The polyelectrolyte film consists of two bUayers of PAH and PSS. (From Ref. 76.)... 

Systems that develop contractile forces are very intriguing as analogues of physiological muscles. The idea for gel muscles was based upon the work of Katchalsky and Kuhn. They have prepared polyelectrolyte films or fibers which become elongated or contracted in response to a change in pH of the surrounding solution, and have estimated the induced force and response time. The contraction of gel fibers is also achieved by electric fields. Use of electric fields has the merit that the signals are easily controlled. 

Amide bond is an effective anchor to connect CNTs to substrate surfaces. Lan et al. [52] covalently assembled shortened multi-walled carbon nanotubes (s-MWNT) on polyelectrolyte films. The shortened MWNT is functionalized with acyl chloride in thionyl chloride (SOCl2) before self-assembling. The FTIR spectrum of self-assem-bled MWNT (SA-MWNT) adsorbed on a CaF2 plate modified with PEI/(PSS/PEI)2 shows two characteristic absorption peaks at 1646cm-1 (amide I bond) and 1524cm-1 (amide II bond) resulting from the amide bond formed between the polyelectrolyte films and s-MWNTs. 

Since the polyelectrolytes contain only one type of mobile ion, the interpretation of conductivity data is greatly simplified. Polyelectrolytes have significant advantages for applications in electrochemical devices such as batteries. Unlike polymer-salt complexes, polyelectrolytes are not susceptible to the build up of a potentially resistive layer of high or low salt concentration at electrolyte-electrolyte interfaces during charging and discharging. Unfortunately flexible polyelectrolyte films suitable for use in devices have not yet been prepared. 

Figure 1.17 AFM image of a gold-nanoparticle-loaded polyelectrolytes film. (Reprinted with permission from Ref [66]. 2003 American Chemical Society.)...

In both cases the top layer of these layered polyelectrolyte films contains many ion sites that can bind redox ions by ion exchange vdth the electrolyte solution. Homo polypeptides such as poly(L-lysine) and poly(L-glutamic add) have been employed to form layered polyelectrolyte films with Fe(CN)6 " electrostatically adsorbed onto ammonium sites in poly(lysine) [45]. Modified electrodes with polyelectrolytes mono-layers have also been deposited using the Langmuir-Blodgett technique [46-48]. 

Polyelectrolyte films are comprised of the polyelectrolytes, solvent and ions, the latter mainly located at the film/solution interface, see below. Solvent content in PEMs can beaproximately40% ]94,95], being the actual value dependent on film history (drying and reswelling steps) and for dry films on environmental humidity ]95,96]. PEMs are therefore highly swollen structures, but its water content is below that found in... 

Due to the presence of interactions, the apparent redox potential of a redox couple inside a polyelectrolyte film can differ from that of the isolated redox couple in solution (i.e. the standard formal redox potential) [121]. In other words, the free energy required to oxidize a mole of redox sites in the film differs from that needed in solution. One particular case is when these interations have an origin in the presence of immobile electrostatically charged groups in the polymer phase. Under such conditions, there is a potential difference between this phase and the solution (reference electrode in the electrolyte), knovm as the Donnan or membrane potential that contributes to the apparent potential of the redox couple. The presence of the Donnan potential in redox polyelectrolyte systems was demonstrated for the first time by Anson [24, 122]. Considering only this contribution to peak position, we can vwite ... 

Figure 2.25 Dependence of the catalytic current for the oxidation of p-D-glucose mediated by the redox polyelectrolyte film for different number of COx layers self-assembled with (PAH-Os) (COx) (n=m = 2, 4, 6). Taken from [182].

The LbL strategy to chemically modify electrodes with redox polyelectrolyte films has become an important tool for the fabrication of devices and electrodes with important future applications in biosensors, electrochromic devices, electrocatalysts, corrosion-resistant coatings, and so on. 

Bmening, M.L. and Rnsling, J. (2006) in Modified Electrodes. Encyclopedia of Electrochemistry Vol. 10 Synthesis of Layered Polyelectrolyte Films (eds A.J. Bard, M. Stratmann, M. Fujihira, J.F. Rnsling and I. Rubinstein), Wdey-VCH, Weinheim. 

The technique of alternating polyelectrolyte film construction has also been adapted to incorporate semiconductors into layered films. For example, multilayer films have been constructed by alternately dipping a quartz substrate into a solution of poly(diallylmethylammonium chloride) and then a solution of a stabilized CdS or PbS colloid (41). The layer-by-layer self-assembly of alternating polymer and metal sulfide is at least partially driven by the electrostatic attraction of the cationic polymer and the negative charge of the stabilized MC colloid particles. 

In another report, layer-by-layer (LbL) self-assembly deposition was employed to prepare the acceptor-sensitizer dyad polyelectrolyte film in DSSC.48 The viologen-containing polymer film with bromide as the counterions... 

Ladam G, Schaaf P, Cuisinier FJ et al (2001) Protein adsorption onto auto-assembled polyelectrolyte films. Langmuir 17 878-882... 

Jewell CM, Zhang J, Fredin NJ et al (2005) Multilayered polyelectrolyte films promote the direct and localized delivery of DNA to cells. J Control Release 106 214-223... 

Dai JH, Bruening ML (2002) Catalytic nanoparticles formed by reduction of metal ions in multilayered polyelectrolyte films. Nano Lett 2 497-501... 

Figure 13.2 Layer-by-layer (LbL) assembly of oppositely charged polyelectrolyte films via electrostatic interactions.10...

A very versatile approach to the formation of multilayer films has been developed by Decher, based on polyelectrolytes. If a solid substrate with ionic groups at the surface is dipped into a solution of a complementary polyelectrolyte, an ultrathin, essentially monomolecular film of the polyion is adsorbed [340]. The adsorption is based on pairing of surface bound ionic sites with oppositely charged ions, bound to the macromolecule. The polymers adsorb in an irregular flattened coil structure and only part of the polymer ions can be paired with the surface ions (Figure 29a). Ionic sites which remain with small counterions provide anchor points for a next layer formed by a complementary polyelectrolyte [342,343]. This way multilayer polyelectrolyte films can be prepared layer-by-layer just by dipping a suitable substrate alternately in an aqueous solution of polyanions and polycations. The technique can be employed with nearly all soluble charged polymers and results in films with a... 

The characteristics of QCM sensors containing mono- or multilayered DNA probe constructed by direct chemical bonding, avidin-biotin interaction or electrostatic adsorption on polyelectrolyte films were compared by Zhou et al. [60]. The use of the polyethyleneimine adhesion, glutaraldehyde cross-linking (PEI-Glu) method to immobilize hepatitis B virus DNA onto gold QCM quartz crystals, enabling the sensor to be regenerated five times, was reported by Hu and co-workers [61],... 

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