Colloids, adsorption electrical properties

As discussed in Chapters 1-7, diffusion, Brownian motion, sedimentation, electrophoresis, osmosis, rheology, mechanics, interfacial energetics, and optical and electrical properties are among the general physical properties and phenomena that are primarily important in colloidal systems [12,13,26,57,58], Chemical reactivity and adsorption often play important, if not dominant, roles. Any physical chemical feature may ultimately govern a specific industrial process and determine final product characteristics, and any colloidal dispersions involved may be deemed either desirable or undesirable based on their unique physical chemical properties. Chapters 9-16 will provide some examples. 

Colloidal particles become electrically charged when they adsorb ions on their surfaces. Adsorption should not be confused with absorption. Adsorption refers to the adhesion of molecules or ions to a surface, whereas absorption refers to the taking in of one material by another material. Adsorption occurs because the atoms or ions at the surface of a particle are not completely surrounded by other atoms or ions as are those in the interior. Consequently, these surface atoms or ions attract and adsorb ions or polar molecules from the dispersion medium onto the surfaces of the colloidal particles. This property is directly related to the large surface area presented by the many tiny particles. 

Of course, the capacitance is an electrical property, which shows up in the context of some electric circuit. In the case of nonconducting materials, as with soil colloids, there are no direct ways to measure or otherwise detect its presence however, the charge separation exists, and the concept of capacitance is present in some treatments and models of adsorption to soil colloids. Furthermore, it is at the origin of the important Stern modification of the GC theory, thus it is relevant to consider here. 

The sorbent materials are supplied as finely dispersed colloidal particles, whose surfaces are smooth. Some of their properties are presented in Table 3. The sorbents cover different combinations of hydrophobicity and sign of the surface charge. Thus, the model systems presented allow systematic investigation of the influences of hydrophobicity, electric charge, and protein structural stability on protein adsorption. 

Jambor, J.L. Dutrizac, J.E. (1998) Occurrence and constitution of natural and synthetic fer-rihydrite, a widespread iron oxyhydroxide. Chem. Rev. 98 2549-2585 James, R.O. ElealyT.W. (1972) Adsorption of hydrolyzable metal ions at the oxide-water interface. Ill A thermodynamic model of adsorption. J. Colloid Interface Sci. 40 65-81 James, R.O. Parks, G.A. (1982) Characterization of aqueous colloids by their electrical double layer and intrinsic surface chemical properties. Surface Colloid Sci. 12 119-126... 

A characteristic feature of colloidal dispersions is the large area-to-volume ratio for the particles involved. At the interfaces between the dispersed phase and the dispersion medium characteristic surface properties, such as adsorption and electric double layer effects, are evident and play a very important part in determining the physical properties of the system as a whole. It is the material within a molecular layer or so of the interface which exerts by far the greatest influence on particle-particle and particle-dispersion medium interactions. 

The special properties of thin liquid films, in particular of foam films, involve studying various colloid-chemical aspects, such as kinetics of thinning and rupture of films, transition from CBF to NBF, isotherms of disjoining pressure, thermodynamic (equilibrium) properties, determination of the electrical parameters of surfactant adsorption layer at the liquid/gas... 

Huang, C. and Stumm, W., Specific adsorption of cations on hydrous gamma-Al203, J. Colloid Interface Sci., 43, 409, 1973, in Characterization of Aqueous Colloids by Their Electrical Double-Layer and Intrinsic Surface Chemical Properties, lames, R.O. and Parks, G.A., Eds., vol. 12 of Surface and Colloid Science, Matijevic, E., Plenum Press, New York, 1982, p. 119. 

The adsorption of charged macromolecules modifies considerably the electrical surface properties of colloid particles already at very low concentration. Figure 1 shows typical dependence of the HF electro-optical effect on the polyelectrolyte concentration. One observes a steep decrease of the effect with increasing polyelectrolyte concentration, which turns to an increase at superequivalent adsorption of the oppositely charged polymer onto the par-... 

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 ... 

The coagulation-dispersion behavior of aqueous silica sols is central to almost all processes requiring their unique adsorption, dispersion, gelation, and sol-gel properties. Aqueous silica sols are of particular interest in colloid science because their coagulation-dispersion behavior is said to be anomalous , that is, their stability in terms of electrolyte-pH control does not follow the pattern followed by almost all other oxide and latex colloidal materials. This chapter examines aqueous silica sol coagulation effects in light of studies of macroscopic silica-water interfaces and in particular the electrical double layer at such interfaces. 

Many properties of disperse systems are related to the distribution of charges in the vicinity of the interface due to the adsorption of electrolytes. The adsorption of molecules is driven by the van der Waals attraction, while the driving force for the adsorption of electrolytes is the longer-range electrostatic (Coulomb) interaction. Because of this, the adsorption layers in the latter case are less compact than in the case of molecular adsorption (i.e., they are somewhat extended into the bulk of the solution), and the discontinuity surface acquires noticeable, and sometimes even macroscopic thickness. This diffuse nature of the ionized adsorption layer is responsible for such important features of disperse systems as the appearance of electrokinetic phenomena (see Chapter V) and colloid stability (Chapters VII, VIII). Another peculiar feature of the adsorption phenomena in electrolyte solutions is the competitive nature of the adsorption in addition to the solvent there are at least two types of ions (even three or four, if one considers the dissociation of the solvent) present in the system. Competition between these ions predetermines the structure of the discontinuity surface in such systems -i.e. the formation of spatial charge distribution, which is referred to as the electrical double layer (EDL). The structure and theory of the electrical double layer is described in detail in textbooks on electrochemistry. Below we will primarily focus on those features of the EDL, which are important in colloid... 

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. 

Organic phosphorus can affect soil properties. Adsorption of organic phosphates affects the charge and electric potential of colloidal particles and, therefore, their dis-persion/flocculation behaviour (Fig. 6.8). The adsorption of myo-inositol hexakis-... 

P. W. Schindler, Surface complexes at oxide-water interfaces, in Adsorption of Inorganics at Solid-Liquid Interfaces (M. A. Anderson and A. J. Rubin, eds.). Ann Arbor Science, Ann Arbor, Mich., 1981. J. A. Davis, R. O. James, and J. O. Leckie, Surface ionization and complexation at the oxide/water interface. I. Computation of electrical double layer properties in simple electrolytes, /. Colloid Interface Sci. 63 480 (1978). 

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