Adsorption ionic

Physical and ionic adsorption may be either monolayer or multilayer (12). Capillary stmctures in which the diameters of the capillaries are small, ie, one to two molecular diameters, exhibit a marked hysteresis effect on desorption. Sorbed surfactant solutes do not necessarily cover ah. of a sohd iaterface and their presence does not preclude adsorption of solvent molecules. The strength of surfactant sorption generally foUows the order cationic > anionic > nonionic. Surfaces to which this rule apphes include metals, glass, plastics, textiles (13), paper, and many minerals. The pH is an important modifying factor in the adsorption of all ionic surfactants but especially for amphoteric surfactants which are least soluble at their isoelectric point. The speed and degree of adsorption are increased by the presence of dissolved inorganic salts in surfactant solutions (14). 

In some cases, e.g., the Hg/NaF q interface, Q is charge dependent but concentration independent. Then it is said that there is no specific ionic adsorption. In order to interpret the charge dependence of Q a standard explanation consists in assuming that Q is related to the existence of a solvent monolayer in contact with the wall [16]. From a theoretical point of view this monolayer is postulated as a subsystem coupled with the metal and the solution via electrostatic and non-electrostatic interactions. The specific shape of Q versus a results from the competition between these interactions and the interactions between solvent molecules in the mono-layer. This description of the electrical double layer has been revisited by... 

As ionic adsorption takes place, normally the potential of zero charge varies linearly with the amount adsorbed.83 Such a variation is used84,85 as a means of extrapolating to zero concentration of the adsorbing sub-... 

A correlation between the amount of adsorbed ions and the electrode potential, in particular E. , has been identified apparently for the first time by Frumkin and Obrutschewa [26Fru]. A minimum of ionic adsorption was found at E, this is equivalent to the absence of specific adsorption at Ep c- The measurement of the amount of adsorbed ions was performed by measuring the ionic concentration in the solution as a function of the electrode potential or by measuring the surface concentration of adsorbed ions by e.g. radiotracer techniques (see also 4.2). (Data obtained with this method are labelled lA). 

The most important physical methods are physical and ionic adsorption on a water-insoluble matrix, inclusion and gel entrapment, and microencapsulation with a liquid or a solid membrane. The most important chemical methods include covalent attachment to a water-insoluble matrix, cross-hnking with the use of a multifunctional, low-molecular weight reagent, and co-cross-linking with other neutral substances, for example proteins. 

Adsorption of ions from the solution. There are two types of ionic adsorption from solutions onto electrode surfaces an electrostatic (physical) adsorption under the effect of the charge on the metal surface, and a specific adsorption (chemisorption) under the effect of chemical (nonelectrostatic) forces. Specifically adsorbing ions are called surface active. Specific adsorption is more pronounced with anions. 

Simpler compounds, like AgNOs, KC1, BaCl2, CuCl2, which show adsorption 5—10 larger than the theoretical figure (these cases may be complicated by dissociation and ionic adsorption, which will be referred to later). 

It will be noted that there should be no ionic adsorption when the interfacial tension is a maximum, as at that point a small alteration in V produces no... 

Enzymes can be immobilized by matrix entrapment, by microencapsulation, by physical or ionic adsorption, by covalent binding to organic or inorganic polymer-carriers, or by whole cell immobilization (5 ). Particularly impressive is the great number of chemical reactions developed for the covalent binding of enzymes to inorganic carriers such as glass, to natural polymers such as cellulose or Sepharose, and to synthetic polymers such as nylon, polyacrylamide, and other vinyl polymers and... 

A change in ionic adsorption in the presence of organic molecules was also observed by Parsons and Zobel. They found that in the presence of acetanilide in the inner layer, the surface concentration of specifically adsorbed phosphate ions decreases. In another work it was suggested that specific adsorption of nitrate ions is markedly reduced in the presence of thiourea in the solution. Thiourea alters the properties of the mercury electrode, affecting even the adsorption of iodides. ... 

The main goal of the molecular dynamics computer simulation of ionic solvation and adsorption on a metal surface has been to test the above model and to provide more quantitative information about the different factors that influence the structure of hydrated ions at the interface. Unfortunately, most of the experimental information about these issues has been obtained from indirect measurements such as capacity and current-potential plots, although in recent years in situ experimental techniques have begun to provide an accurate test of the above model. For a recent review of experimental techniques and the theory of ionic adsorption at the water/metal interface, see the excellent paper by Philpott. ... 

Both cationic adsorption and anionic adsorption belong to what is called ionic adsorption. Covalent adsorption is due to the localized covalent bonding, and metallic adsorption is due to the delocalized covalent bonding. The distinction among these three modes of chemisorption, however, is not so definite that the transition from the covalent through the metallic to the ionic adsorption may not be discontinuous, but rather continuous, in the same way as the transition of the three-dimensional solid compounds between the covalent, metallic, and ionic bonding. 

If the solid diaphragm material adsorbs both hydrogen and hydroxyl ions it is evident that electric endosmose will cease when equal ionic adsorption has taken place, the double layer potential or electrokinetic potential being at this point zero and the diaphragm is at the isoelectric point. 

There exist a number of membranes which are permeable to some ions and not to others, and these give rise to definite potential differences when the membrane is interposed between two solutions of the electrolyte. These membranes must be considered capillary in structure and selective permeability attributed to selective ionic adsorption, or in some cases to restriction imposed by the size of the capillaries. 

On the addition of small quantities of electrolyte all the amicrons are not discharged by ionic adsorption. Only those that are completely discharged or those for which the electrokinetic potential has been reduced below the critical maximum will actually adhere to one another on contact. We should thus with... 

If the non-electrolytes are in fact selectively adsorbed it necessarily follows that the ions are displaced from the colloid surface thus the non-electrol3 te cuts dovm the adsorption of the ions of the added electrolyte. It has already been noted that the anions and cations of an added salt are not equally adsorbed and it is likely that the extent to which the ionic adsorption is cut down by the preferential adsorption of the non-electrolyte is not equal for each ion. In the case of the negative arsenious sulphide sol if the non-electrolyte cuts down the adsorption of the cation of an... 

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