Colloid-polymer surface layers, electrical

Charge neutralization, polymeric flocculation effect, 4-5 Colloid-polymer surface layers, electrical and hydrodynamic properties investigated with electro-optics, 121-135 Colloid stability, 161 Colloidal particles, polymer-induced attraction, 97... 

Radeva, T., Petkanchin, 1., and Varogui, R., Electrical and hydrodynamic properties of colloid-polymer surface layers investigated by electro-optics, Langmuir, 9, 170, 1993. 

Application of Electro-optics To Investigate the Electrical and Hydrodynamic Properties of Colloid—Polymer Surface Layers... 

The second part is devoted to adsorption of polyelectrolytes at interfaces and to flocculation and stabilization of particles in adsorbing polymer solutions. A recent theory of the electrostatic adsorption barrier, some typical experimental results, and new approaches for studying the kinetics of polyelectrolyte adsorption are presented in the first chapter of this part. In the following chapters, results are collected on the electrical and hydrodynamic properties of colloid-polyelectrolyte surface layers, giving information on the structure of adsorbed layers and their influence on the interactions between colloidal particles examples and mechanisms are analyzed of polyelectrolyte-induced stabilization and fragmentation of colloidal aggregates ... 

It is important to note that the concept of osmotic pressure is more general than suggested by the above experiment. In particular, one does not have to invoke the presence of a membrane (or even a concentration difference) to define osmotic pressure. The osmotic pressure, being a property of a solution, always exists and serves to counteract the tendency of the chemical potentials to equalize. It is not important how the differences in the chemical potential come about. The differences may arise due to other factors such as an electric field or gravity. For example, we see in Chapter 11 (Section 11.7a) how osmotic pressure plays a major role in giving rise to repulsion between electrical double layers here, the variation of the concentration in the electrical double layers arises from the electrostatic interaction between a charged surface and the ions in the solution. In Chapter 13 (Section 13.6b.3), we provide another example of the role of differences in osmotic pressures of a polymer solution in giving rise to an effective attractive force between colloidal particles suspended in the solution. 

More detailed and advanced information on these forces can be found in the book by Israelachvili (1991), which is devoted completely to intermolecular and surface forces. Here, we focus on the essential basic information and examples. Before we proceed to a physical explanation of these forces and the necessary equations, it is useful to explore the role played by the van der Waals forces in colloid stability since this theme reappears in our discussions of electrical double-layer forces in Chapter 11 and polymer-induced forces in Chapter 13. 

Addition of soluble macromolecules (polymers) in the colloidal dispersion can stabilize the colloidal particles due to the adsorption of the polymers to the particle surfaces. The soluble polymers are often called protective agents or colloids. If the protective agents are ionic and have the same charge as the particles, the electrical double-layer repulsive forces will be increased and thus the stability of the colloidal particles will be enhanced. In addition, the adsorbed polymers may help weaken the van der Waals attraction forces among particles. However, the double-layer repulsion and the van der Waals attraction cannot account for the entire stabilization of the particle dispersions. 

In conventional latices, the colloidal stability of the particles arises from the predominance of the electrostatic forces of repulsion over the London-van der Waal s forces of attraction. These electrostatic forces of repulsion result from the electric double layer formed by the emulsifier ions adsorbed on the hydrophobic polymer particle surface and the counterions from the aqueous phase. The London-van der Waal s forces of attraction are strongest when the particle-particle distance is very small. Therefore, in most particle-particle collisions, the particles repel one another until the particle-particle distance is decreased to the point where the London-van der Waal s forces of attraction are predominant over the electrostatic forces of repulsion. Thus, many conventional latices remain stable indefinitely without significant stratification or flocculation of the particles. 

But often more important than the effects of the electrolytes that influence the thickness of the electric double layer are many solutes that, upon adsorption onto the colloid surface, reduce or modify the surface charge. The specific adsorption of H, OH, metal ions, and ligands (as well as the attachment of polymers) to the colloid surface affects the surface charge and the surface potential and, in turn, the colloid stability. 

Although this book significantly differs from the earlier Colloid Chemistry textbook, it nevertheless focuses on the specifics of educational and research work carried out at the Colloid Chemistry Division at the Chemistry Department of MSU. Many results presented in this book represent the art developed in the laboratories of the Colloid Chemistry Division, in the Laboratory of Physical-Chemical Mechanics (headed by E.D. Shchukin since 1967) of the Institute of Physical Chemistry of the Russian Academy of Science, and in other research institutions and industrial laboratories under the guidance of the authors and with their direct participation. Special attention is devoted in the book to the broad capabilities that the use of surfactants offers for controlling the properties and behavior of disperse systems and various materials due to the specific physico-chemical interactions taking place at interfaces. At the same time the authors made every effort to avoid duplication of material traditionally covered in textbooks on physical chemistry, electrochemistry, polymer chemistry, etc. These include adsorption from the gas phase on solid surfaces (by microporous adsorbents), the structure of the dense part of the electrical double layer, electrocapillary phenomena, specific properties of polymer colloids, and some other areas. 

---