Strength sorption

Sorption of nonionic, nonpolar hydrophobic compounds occurs by weak attractive interactions such as van der Waals forces. Net attraction is the result of dispersion forces the strength of these weak forces is about 4 to 8 kj/mol ( 1 2 kcal/mol). Electrostatic interactions can also be important, especially when a molecule is polar in nature. Attraction potential can develop between polar molecules and the heterogeneous sod surface that has ionic and polar sites, resulting in stronger sorption. 

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). 

Fig. 3. Effects of composition on physical properties. A, acetyl B, butyryl C, cellulose. 1, increased tensile strength, stiffness 2, decreased moisture sorption 3, increased melting point 4, increased plasticizer compatibiUty 5, increased solubiUties in polar solvents 6, increased solubiUties in nonpolar...

To improve the rheological properties and extend the very short working time, a simple polyester is kicluded as thinner. Mixing is easy, and dimensional change ki ak is less than 0.1% over several hours. Elastic recovery and reproduction of detail are exceUent. The elastomeric cycHc imine impression materials have a higher modulus of elasticity than the condensation siHcone or polysulfide mbbers, and are more difficult to remove from the mouth. The materials have relatively low tear strength and an equUibrium water sorption of 14% thus, polyether impression materials tear readily. Because of thek poor dimensional stabUity ki water, they should be stored ki a dry environment. 

The second type of interaction, displacement interaction, is depicted in Figure 10. This type of interaction occurs when a strongly polar solute, such as an alcohol, can interact directly with the strongly polar silanol group and displaces the adsorbed solvent layer. Depending on the strength of the interaction between the solute molecules and the silica gel, it may displace the more weakly adsorbed solvent and interact directly with the silica gel but interact with the other solvent layer by sorption. Alternatively, if solute-stationary phase interactions are sufficiently strong, then the solute may displace both solvents and interact directly with the stationary phase surface. 

The equilibrium swelling degree is the most important property of a hydrogel it directly influences the rate of water sorption, the permeability to drugs, and the mechanical strength of the gel. It also affects the biocompatibility of the... 

The pH-dependence of metal sorption by bacteria can vary significantly with metal concentration. For example, the sorption of Pb by Pseudomonas atlantica at the highest metal concentration (5x10-6 M) was almost independent of pH, whereas sorption markedly increased with pH when the metal concentration was low (Ledin 2000). On the other hand, the accumulation of Cd by Pseudomonas cepacia showed an increased pH dependence with increasing metal concentration (Savvaidis et al. 1992). The pH dependence may also be influenced by ionic strength. 

Small TD, Warren LA, Ferris FG (2001) Influence of ionic strength on strontium sorption to bacteria, Fe(III) oxide and composite bacteria-Fe(III) oxide surfaces. Appl Geochem 16 939-946... 

Sabljic, A. (1984) Predictions of the nature and strength of soil sorption of organic pollutants by molecular topology. J. Agric. Food Chem. 32, 243-246. 

Peng, J., Wan, A. (1998) Effect of ionic strength on Henry s law constant of volatile organic compounds. Chemosphere 36, 2731-2740. Peng, J., Wan, A. (1998) Effect of ionic strength on Henry s constants of volatile organic compounds. Chemosphere 36, 2731-2740. Pennell, K.D., Rhue, R.D., Rao, P.S.C., Johnston, C.T. (1992) Vapor-phase sorption of p-xylene and water on soils and clay minerals. Environ. Sci. Technol. 26, 756-763. 

Solid phase extraction (SPE) involves the separation of components of samples in solution through their selective interaction with and retention by a solid, particulate sorbent. SPE depends on differences in the affinities of the various components of the sample for the sorbent. The mechanisms of the interactions are virtually identical to the sorption processes that form the basis of liquid chromatographic separations (p. 80). The choice of solvent, the pH and ionic strength of aqueous solutions, and the chemical nature of the sorbent surface, especially its polarity, are all of importance in controlling the selectivity and efficiency of an extraction. 

The preparation methods of aluminum-deficient zeolites are reviewed. These methods are divided in three categories (a) thermal or hydrothermal dealumination (b) chemical dea-lumination and (c) combination of thermal and chemical dealumination. The preparation of aluminum-deficient Y and mordenite zeolites is discussed. The structure and physico-chemical characteristics of aluminum-deficient zeolites are reviewed. Results obtained with some of the more modern methods of investigation are presented. The structure, stability, sorption properties, infrared spectra, acid strength distribution and catalytic properties of these zeolites are discussed. 

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