Colloidal systems polyelectrolytes

In the latter case the total interaction, which is what can be measured, is affected by the net charge of the surface and the adsorbed layer, ion-ion correlations, bridging interactions and steric confinement of the polymer chain [116]. We note that polyelectrolytes are often present as additives in colloidal dispersions and the character of the forces generated by the polyelectrolyte adsorption layers has a paramount influence on stability of these colloidal systems. With the aim to illustrate what can be learnt about polyelectrolyte adsorption layers using the SFA, we will look at the influence of the polyelectrolyte charge density on the forces acting between surfaces coated with polyelectroytes. We will consider an example where the polyelectrolyte charge density is varied by a systematic... 

Electric double layers at phase boundaries pervade the entire realm of Interface and colloid science. Especially in aqueous systems, double layers tend to form spontaneously. Hence, special precautions have to be taken to ensure the absence of charges on the surfaces of particles. Insight into the properties of double layers is mandatory, in describing for Instance electrosorption, ion exchange, electrokinetics (chapter 4), charged monolayers (Volume III), colloid stability, polyelectrolytes and proteins, and micelle formation of ionic surfactants, topics that are intended to be treated in later Volumes. The present chapter is meant to Introduce the basic features. 

D.G. Hall. Thermodynamics of Solutions of Polyelectrolytes, Ionic Surfactants and Other Colloidal Systems, J. Chem. Soc. Faraday Trans. I 77 (1981) 1121-56. (Paper with a review nature.)... 

Rodlike polyelectrolytes have been known for a long time. Biological polymers such as DNA [4-8] and xanthane [9-12], or colloidal systems like the ferredoxin virus [13, 14] and the tobacco mosaic virus (TMV) [15, 16], may be the most prominent examples. However, there were also publications on some synthetic rods in the early 1990s when we started our program. Poly(p-phenylene-benzobisoxazoles) and poly(p-phenylene-benzobisthia-zoles) may serve as examples [17-20]. Nevertheless, new rodlike polyelec-... 

The set of results presented here allows us to understand better the properties of polyelectrolytes in the presence of multivalent counterions. However, these systems are very complex, and we hope that future experimental and theoretical work will permit us to progress significantly. We must keep in mind that while polyelectrolytes and multivalent counterion systems are interesting from a fundamental point of view, they are also of practical interest, as for instance in the biological field and in depollution process. An extension to polyelectrolyte/charged colloid systems that present some complex phase diagrams is in progress. 

Interesting peculiarities of mass transfer processes are observed in fine membranes permeable to ions but impermeable to colloidal particles (semipermeable membranes, e.g. collodium film). If such a membrane separates colloidal system or polyelectrolyte solution from pure dispersion medium, some ions pass through the membrane into the dispersion medium. Under the steady-state conditions the so-called Donnan equilibrium is established. By repeatedly replacing the dispersion medium behind the membrane, one can remove electrolytes from a disperse system. This method of purifying disperse systems and polymer solutions from dissolved electrolytes is referred to as the dialysis. 

Particle charge plays a major role on the stabilization of colloidal systems. Especially when nanoparticles are stabilized by an adsorption layer of polyelectrolytes, zeta potential measurements are very useful. The stabilization of the nanoparticles results from a combination of ionic and steric contributions. The zeta potential can be detected by means of electro-osmosis, electrophoresis, streaming potential, and sedimentation potential measmements. The potential drop across the mobile part of electric donble layer can be determined experimentally, whenever one phase is made... 

In addition to these technological developments, the range of applications of aqueous SEC has increased dramatically. Size and size distributions can be determined for colloidal systems, pre-eminently micellar aggregates of either synthetic or natural surfactants. In principle, one may also obtain information about the association equilibrium in such systems. The use of aqueous SEC to evaluate equilibrium constants for the binding of smaller molecules to larger ones by the Hummel-Dryer method and related techniques is well documented. Ligand/macromolecular systems studied in this way include small ion/protein, substrate/enzyme, and protein/polyelectrolyte mixtures. The perturbation of ionic concentrations by polyelectrolytes, i.e. the Donnan effect, is also susceptible to a similar approach. 

Jvd G, Spruijt E, Lemmers M, Cohen Stuart MA (2011) Polyelectrolyte complexes bulk phases and colloidal systems. J Colloid Interface Sci 361 407-422. doi 10.1016/j.jcis.2011.05.080... 

The osmotic stress method has also been applied to colloidal dispersions [1238,1246], emulsions [1247], colloidal crystals [1248], clays [1249, 1250], block copolymers [1251], a mixed nanoparticle/polymer system [1252], and colloids with polyelectrolyte multilayers [1253]. 

Polyelectrolytes provide excellent stabilisation of colloidal dispersions when attached to particle surfaces as there is both a steric and electrostatic contribution, i.e. the particles are electrosterically stabilised. In addition the origin of the electrostatic interactions is displaced away from the particle surface and the origin of the van der Waals attraction, reinforcing the stability. Kaolinite stabilised by poly(acrylic acid) is a combination that would be typical of a paper-coating clay system. Acrylic acid or methacrylic acid is often copolymerised into the latex particles used in cement sytems giving particles which swell considerably in water. Figure 3.23 illustrates a viscosity curve for a copoly(styrene-... 

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