Adsorbent surface activity

These surface active agents have weaker intermoiecular attractive forces than the solvent, and therefore tend to concentrate in the surface at the expense of the water molecules. The accumulation of adsorbed surface active agent is related to the change in surface tension according to the Gibbs adsorption equation... 

Electrokinetic processes are widely used in different fields of science and technology. We had already mentioned the use of electrokinetic processes for research into the electric properties of surface layers of insulating materials. Such measurements are used, in particular, when studying the surface properties of polymeric materials, their behavior in different media, and their interactions with other materials (e.g., with adsorbing surface-active substances). The results of this research are used in textile, cellulose and paper, and other industries. 

Fig. 12.1.5 Polymer encapsulation of inorganic particles by polymerization of adsorbed surface active monomer.

Surfaces which are not normally hydrophobic, such as untreated mica or silica, still have a great propensity to adsorb surface active molecules. Silica... 

Non-Ionics of the C E -type have a very typical solubility behaviour, which is related to the EO-water interaction, hydration for short. First, poly(ethylene oxide), (PEO)jj is fairly soluble in water at room temperature, but polylpropylene oxide) (PPO) is not (as expected), and neither is poly(methylene oxide) (PMO), (unexpected). This irregular trend reminds us that solubility is not only determined by hydration in solution, but also by the Gibbs energy in the crystalline phase, which will be related to the molecular packing therein. Based on this difference in solubility, and hence in adsorbability, surface active polymers of the PEO-PPO type have been synthesized [Pluronics]-, they have a wide scope of application. 

Batina, N., Ruzic, I., and Cosovic, B. (1985) An Electrochemical Study of Strongly Adsorbable Surface-Active Substances. Determinations of Adsorption Parameters for Triton-X-100 at the Mercury/Sodium Chloride Interface, J. Electroanal. Chem. Interfacial Electrochem. 190, 21-32. 

Eluent strength is assumed to increase in the order i< 2< 3 for solvents A, B, and C 2 and are the effective molecular areas of adsorbed solvent molecules B and C, respectively (with the exception of certain very strong solvents) X2 and X are the mole fractions of B and C in the solvent mixtures and a represents the adsorbent s surface activity. To use Eqs. 1 and 2, we must know the activity degree of the adsorbent. Consequently, the a (adsorbent surface activity function) values for a few adsorbents with respect to water content are presented in Table 2. Based on the data in Tables 1 and 2, and by using Eq. 1, an infinite number of such series can be established. 

Among the polar adsorbents, surface activity is intimately related to adsorbent water content. Almost all polar adsorbents lose water upon being heated, the water existing originally in the adsorbent as either (1) bulk water unassociated with the surface, (2) surface hydroxyl groups which... 

Normally the difference in log A" values for two isomers will be proportional to the adsorbent surface activity function a [Eq. (6-6a)], rather than to the function a, of Eq. (11-3). st, varies with alumina water content as shown in Fig. 11-7 whereas a decreases from 1.0 to 0.6 between 0% and... 

An earlier derivation of Eq. (9-2a) (8), where the term (—aja) was defined as e , assumes that the quantity is proportional to adsorbent surface activity a. This is not generally true, however. As we have seen in Chapters 6 and 7, a tends to change markedly with changes in adsorbent activation temperature or the addition of water to the adsorbent, corresponding to the appearance or disappearance of strong adsorbent sites. Dispersion interactions and are much less sensitive to changes in adsorbent surface structure than are selective interactions and a. The parameter exhibits much less variation with differences in adsorbent treatment than does a. This is illustrated in Fig. 9-2, where values of... 

That is, a change in separation temperature is equivalent to a change in the value of the adsorbent surface activity function a. Higher temperatures... 

As we have shown, the surface forces at an interface depend upon the surface tension gradients there. If adsorbed surface-active materials are distributed at an interface, then this distribution must be known to determine the surface forces, since the surface tension gradients depend on the local surface concentration of adsorbed material. The surface mass concentration of the adsorbed substance follows from an interfacial mass balance. 

It was shown in [77] that, irrespective of the electrolyte concentration, for a surface coverage exceeding 20%, the portion of adsorbed surface active l l-charged ions bonded to counterions in the S-H layer is approximately 90%, that is, the surface layer is almost electroneutral. The calculations performed in [80] for sodium tetradecyl sulphate solutions, with or without added NaCl, revealed that the extent of bonded counterions, while being somewhat lower than that reported in [77], is quite high, and amounts up to 80% for concentrated solutions. These results... 

The formation of a two-dimensional viscous layer along the surface. Repulsive interactions between adsorbed layers Adsorbed surface-active components, e.g. proteins, peptides and lipids. Absences of defoaming components such as free oil... 

Latex particles make excellent adsorption surfaces in scientific experiments (206). The latex particles have a specific capacity to adsorb surface active materials, and for this reason, are useful in quantitative adsorption... 

Suppositories are solid, single-dose preparations. Their shape, volume and consistency make them suitable for rectal administration. They contain one or more active substances dispersed or dissolved in a suitable basis that may be soluble or dispersible in water or may melt at body temperature. Excipients such as diluents, adsorbents, surface-active agents, lubricants, antimicrobial preservatives and colotulng matter, authorised by the competent authority, may be added if necessary (Ph. Eur.). 

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