Electrostatic attraction, adsorption

In a second hypothesis, one can consider that the adsorption is mainly due to hydrogen bonds and that electrostatic attraction between polymer and particles only brings them together. In such case, the influence of c and r on the stability should be related to the number of amide groups available for hydrogen bounds and the increase of salinity should lead to the collapse of the chain and reduce the probability of interparticles bridging. 

In summary, the removal of organic matter and Fe oxides significantly changes the physicochemical and surface chemical properties of soils. Thus, this pretreatment affects the overall reactivity of heavy metals in soils. The removal of organic matter and Fe oxides may either increase or decrease heavy metal adsorption. The mechanisms responsible for the changes in metal adsorption in soils with the removal of organic matter and Fe oxides include increases in pH, surface area, CEC and electrostatic attraction, decreases in the ZPC, shifts of positive zeta potentials toward... 

Polyelectrolytes. The most striking feature of polyelectrolytes is that due to the electrostatic repulsion between the segments, the formation of thick adsorbed layers is prevented. Polyelectrolytes tend to adsorb in rather flat conformations. If adsorbent and polyelectrolyte bear opposite charges, this attraction can be of an electric (coulombic) nature if the charges have the same sign, adsorption takes place only if the non-electrostatic attraction outweighs the electrostatic repulsion (Lyklema, 1985). 

The nature of bonding is not only dependent on the atomic arrangement, molecular conformation and chemical constitution of the fiber and matrix, but also on the morphological properties of the fiber and the diffusivity of elements in each constituent. It follows therefore that the interface is specific to each fiber-matrix system (Kim and Mai, 1991). Adhesion in general can be attributed to mechanisms including, but not restricted to, adsorption and wetting, electrostatic attraction. 

The selective adsorption of the hydrogen ions cannot proceed to tr ue equilibrium owing to the electrostatic attraction between the dissimilar ions, consequently chlorine ions are adsorbed in excess of their equilibrium concentration and since the hydrogen ions on adsorption have to do work in increasing the surface concentration of chlorine ions above their proper value, the true adsorption value of the hydrogen ions is not attained. 

On the addition of a neutral chloride to the solution the chlorine ion concentration is increased, and provided that the cation of the added chloride does not affect the adsorption of the hydrogen ion, i.e. on addition of a weakly adsorbed cation, such as potassium, the adsorption of the hydrogen ion can now proceed to its normal equilibrium value without having to retain any adsorbed chlorine ions by electrostatic attraction. The addition of potassium chloride to a hydrochloric acid solution will thus augment the adsorption of the acid by the charcoal, a result confirmed by Michaelis and Rona. 

Dissolved polymer molecules can be adsorbed by polymer particles via electrostatic attractive force or hydrophobic interaction. When polyelectrolyte is adsorbed on an opposite-charge particle, the polymer molecules usually have a loop-and-tail conformation and, as a result, inversion of charge occurs. For example, sulfatecarrying particles behave as cationic ones after they adsorb poly(lysine). Then poly(-styrene sulfonate) can be adsorbed on such cationic particles and reinvert the charge of particles to anionic (14). Okubo et al. pointed out that the alternate adsorption of cationic and anionic polymers formed a piled layer of polyelectrolytes on the particle, but the increment of adsorbed layer thickness was much less than expected. This was attributed to synchronized piling of two oppositely charged polyelectrolytes (15). 

Figure 11.1. Schematic views of various ways in which an organic chemical, i, may sorb to natural inorganic solids (a) adsorption from air to surfaces with limited water presence, (b) partitioning from aqueous solutions to the layer of vicinal water adjacent to surfaces that serves as an absorbent liquid, (c) adsorption from aqueous solution to specific surface sites due to electron donor-acceptor interactions, (d) adsorption of charged molecules from aqueous solution to complementarily charged surfaces due to electrostatic attractions, and (e) chemisorption due to surface bonding or inner sphere complex formation.

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