Polyelectrolyte film structure

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... 

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... 

Only a few studies about aqueous films of amphiphilic random polyelectrolytes are reported in the literature. Millet et al. [239-241] have investigated by x-ray reflectivity the behavior of vertical free-standing films (Figure 29) of a series of hydrophobically modified poly(acrylic acid) sodium salt (HMPAANa) and poly(acrylic acid) (HMPAAH). The chemical structure of the polymer was presented in Sec. II.C (Eq. 2a). One of the aims of this work was to determine the microscopic structure of the films to explain the (macroscopic) stability behavior of the dodecane-in-water emulsions studied by Perrin et al. [188,189], who used the same series of amphiphilic polyelectrolytes as primary emulsifiers. The aqueous polyelectrolyte films have been used as model systems for the interstitial films separating two neighboring oil droplets of an emulsion creamed layer. The authors have assumed that the oil/water interface encountered in emulsions was suitably described by the air/water interface of the films. The HMPAANa and HMPAAH co-... 

J. Schmitt, T. Grunewald, G. Decher, P.S. Pershan, J. Kjar and M. Losche, Internal structure of layer-by-layer adsorbed polyelectrolyte films a neutron and X-ray reflectivity study, Macromolecules, 1993, 26, 7058 D.M. Kaschak, J.T. Lean, C.C. Waraksa, G.B. Saupe, H. Usami and T.E. Mallouk, Photoinduced energy and electron transfer reactions in lamellar polyanion/polycation thin films, J. Am. Chem. 

Steitz R, Leiner V, Siebrecht R, Klitzing Rv. 2000. Influence of the ionic strength on the structure of polyelectrolyte films at the solid/liquid interface. Colloids Surf A 163(1) 63 70. 

A final important motif for self-assembly of CPEs is by LbL deposition of polyelectrolyte multilayer films. The LbL multilayer film deposition method was first introduced by Decher [37,38], and since then it has been used to fabricate nanostructured films using a wide variety of synthetic and naturally occurring polyelectrolytes [39]. Deposition of LbL films involves a very simple sequence of alternately dipping a substrate into solutions that contain a cationic polyelectrolyte and an anionic polyelectrolyte. The sequential LbL deposition method leads to formation of polymer multilayer film structures. A single... 

Control of the assembly of multilayer polyelectrolyte films and the incorporation of metal ions provide the possibility for development of polymer matrices characterized by a varying content and distribution of the metal ions. The spatial localization of Ag" " within multilayer polyelectrolyte films was realized using two different types of bilayer building blocks [104]. By adding fully ion-paired oppositely charged polyelectrolyte, a series of PAH/PAA bilayers, which do not include metal ions, can be inserted between the bUayers, which contain Ag. This technique allows one to prepare a sandwich-like metallo-containing film structure. 

Duval, J. F. L., KUttner, D., Nitschke, M., Wemer, C., Zimmermann, R. (2011). Interrelations between chaiging, structure and electrokinetics of nanometric polyelectrolyte films. Journal of Colloid arul Interface Science, 362,439-449. 

Garg, A., Heflin, J.R., Gibson, H.W., Davis, R.M. Study of film structure and adsorption kinetics of polyelectrolyte multilayer films effect of pH and polymer concentration. Langmuir 24, 10887-10894 (2008)... 

Schmitt, J., et al.. Internal structure of layer-by-layer adsorbed polyelectrolyte films a neutron and X-ray reflectivity study. Macromolecules, 1993. 26 p. 7058-7063. 

Gergely, C., Bahi, S., Szalontai, B., Flores, H., Schaaf, R, Voegel, J.-C., Cuisinier, F. J. C. Human serum albumin self-assembly on weak polyelectrolyte multilayer films structurally modified by pH changes. Langmuir, 2004,20, 5575-5582. 

Functionalized polyelectrolytes are promising candidates for photoinduced ET reaction systems. In recent years, much attention has been focused on modifying the photophysical and photochemical processes by use of polyelectrolyte systems, because dramatic effects are often brought about by the interfacial electrostatic potential and/or the existence of microphase structures in such systems [10, 11], A characteristic feature of polymers as reaction media, in general, lies in the potential that they make a wider variety of molecular designs possible than the conventional organized molecular assemblies such as surfactant micelles and vesicles. From a practical point of view, polymer systems have a potential advantage in that polymers per se can form film and may be assembled into a variety of devices and systems with ease. 

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