Polyelectrolytes flexible structures

A desirable property of non-ionic xerogellants is their natural insensitivity to the presence of ionic solutes in the fluid being absorbed. Unlike polyelectrolytes, non-ionics can gel as much urine as pure water. A critical impediment to the effective utilization of the poly(ethylene-oxide) xerogellants in disposable diapers is the soft, almost flowable, nature of the gel. Even fully hydrated, the polyether macromolecule is a flexible coil. This flexible structure is manifested as weakness of the highly swollen gels. Increasing the crosslink density stiffens the gel but reduces swellability. 

As a polycation, chitosan spontaneously forms macromolecular complexes upon reaction with anionic polyelectrolytes. These complexes are generally water-insoluble and form hydrogels [90,91]. A variety of polyelectrolytes can be obtained by changing the chemical structure of component polymers, such as molecular weight, flexibility, fimctional group structure, charge density, hydrophilicity and hydrophobicity, stereoregularity, and compatibility, as... 

FIG. 1 Geometries of electrolyte interfaces, (a) A planar electrode immersed in a solution with ions, and with the ion distrihution in the double layer, (b) Particles with permanent charges or adsorbed surface charges, (c) A porous electrode or membrane with internal structures, (d) A polyelectrolyte with flexible and dynamic structure in solution, (e) Organized amphophilic molecules, e.g., Langmuir-Blodgett film and microemulsion, (f) Organized polyelectrolytes with internal structures, e.g., membranes and vesicles. 

From the physics point of view, the system that we deal with here—a semiflexible polyelectrolyte that is packaged by protein complexes regularly spaced along its contour—is of a complexity that still allows the application of analytical and numerical models. For quantitative prediction of chromatin properties from such models, certain physical parameters must be known such as the dimensions of the nucleosomes and DNA, their surface charge, interactions, and mechanical flexibility. Current structural research on chromatin, oligonucleosomes, and DNA has brought us into a position where many such elementary physical parameters are known. Thus, our understanding of the components of the chromatin fiber is now at a level where predictions of physical properties of the fiber are possible and can be experimentally tested. 

Another very interesting class of crosslinked polyelectrolytes are the so-called superabsorbents. They predominantly consist of crosslinked and (partially) neutralized poly(acrylic acid) and, hence, represent a network of flexible polymer chains that carry dissociated, ionic groups. Due to this structure they can function as water-swellable gels. Although they are hard, sandy powders in a dry... 

The loss in effectiveness in 0.1M Na2S04 is particularly drastic. The high salt concentrations must surely influence the solvation characteristics of the polyelectrolyte and change the thermodynamic quality of the solvent. The effects on the solution structure and the flexibility of the polymer backbone must also be discussed in this connection, as, for example, suggested by Brostow (1984). 

Flexible polyelectrolytes exhibit conformational variations when the interaction strength (ZB) or the density of a system is changed. Hence, the structure factor is no longer an a priori known quantity but has to be determined in a self-consistent manner. This is achieved by casting the underlying multichain interactions into a medium-induced interaction potential among the... 

To elucidate the structure of a solution of flexible polyelectrolytes, we again use the integral equation theory approach of Sect. 2.2. The necessary structure factor is determined self-consistently using the reference chain (9) of the last section. The intermolecular interactions are taken into account by a medium-induced intramolecular potential [35, 47,48]... 

The monomer-monomer correlation functions of flexible polyelectrolytes exhibit qualitatively the same behavior as those for rod-like molecules. The conformational changes, however, result in more pronounced and shifted peaks. From Fig. 8 we deduce a shift of the peaks of flexible chains to larger distances compared to those of rod-like chains. This is a consequence of a smaller overlap between flexible chains compared to the one between rodlike molecules. Naturally, the effect is most pronounced for densities larger than the overlap densities. The increased peak intensity corresponds to a more pronounced order in the system of flexible chains, and is a result of the more compact structure of a polymer coil. (The structural properties of flexible polyelectrolytes without medium-induced potential have been studied in [48].)... 

Table 8). This permits the interpretation of experimental data by using the electro-optical properties of flexible-chain polymers in terms of a worm-like chain model However, EB in solutions of polyelectrolytes is of a complex nature. The high value of the observed effect is caused by the polarization of the ionic atmosphere surrounding the ionized macromolecule rather than by the dipolar and dielectric structure of the polymer chain. This polarization induced by the electric field depends on the ionic state of the solution and the ionogenic properties of the polymer chain whereas its dependence on the chain structure and conformation is slight. Hence, the information on the optical, dipolar and conformational properties of macromoiecules obtained by using EB data in solutions of flexible-chain polyelectrolytes is usually only qualitative. Studies of the kinetics of the Kerr effect in polyelectrolytes (arried out by pulsed technique) are more useful since in these... 

It is well known that C60 neither reacts with nor is adsorbed by bare silica, but it reacts with Si-H bonds on H-terminated silicon wafers forming covalently bonded monolayers [94]. The introduction of C60 dissolved in toluene should occur in the interfacial region between the PVFA-co-PVAm chains which are adsorbed on to silica and transform the reversibly adsorbed and flexible polyelectrolyte layer into an irreversibly adsorbed and more rigid structure. However, amino groups inside the adsorbed PVFA-co-PVAm coils are not available for surface functionalization with C60 (Scheme 5). Never-... 

It has been shown that the chemical nature of the polymer cushion can be very flexible with examples ranging from polyelectrolytes to carbohydrate-containing macromolecules and cross-linked hydrogels. So far, the cushion has played only a rather passive role in that it was almost exclusively used as a structural element in the build-up of the tethered membrane architectures. The real potential, however, lies in the fact that these polymer systems could play a crucial functional role for these... 

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