Preferential diffusion

Adsorption is an entropically driven process by which molecules diffuse preferentially from a bulk phase to an interface. Due to the affinity that a surfactant molecule encounters towards both polar and non-polar phases, thermodynamic stability (i.e. a minimum in free energy or maximum in entropy of the system) occurs when these surfactants are adsorbed at a polar/non-polar (e.g. oil/water or air/water) interface. The difference between solute concentration in the bulk and that at the interface is the surface excess concentration. The latter... 

However, liquid-liquid extraction can form emulsions, and the extractant is usually expensive and sometimes toxic to the cell culture (Diirre, 1998). To solve these problems, the perstraction technique was developed based on the liquid-liquid extraction concept. In the perstraction separation process, the fermentation broth and the extractant are separated by a membrane, where two immiscible phases can exchange butanol. In this process, butanol can diffuse preferentially across the membrane, while other components (substrates, cell culture, and other fermentation products) are retained in the fermentation broth. This strategy effectively avoids the potential problems in the liquid-liquid extraction system, but it needs to point out that... 

A seminal paper by Sata and co-workers showed that ion conductivity in BaFg/CaFg heterolayers is tuneable by changing the thickness of the individual BaFg or CaFg films optimum conductivity was achieved for films with nanometre thicknesses. Computer simulations on this system revealed that the F ions diffuse preferentially at interfacial and grain-boundary regions, which helped explain the observed thickness-tuned conductivity. ... 

Jet separator. An interface in which carrier gas is preferentially removed by diffusion out of a gas jet flowing from a nozzle. Jet separator, jet-orifice separator, jet enricher, and jet orifice are synonymous terms. 

Catalytic Properties. In zeoHtes, catalysis takes place preferentially within the intracrystaUine voids. Catalytic reactions are affected by aperture size and type of channel system, through which reactants and products must diffuse. Modification techniques include ion exchange, variation of Si/A1 ratio, hydrothermal dealumination or stabilization, which produces Lewis acidity, introduction of acidic groups such as bridging Si(OH)Al, which impart Briimsted acidity, and introducing dispersed metal phases such as noble metals. In addition, the zeoHte framework stmcture determines shape-selective effects. Several types have been demonstrated including reactant selectivity, product selectivity, and restricted transition-state selectivity (28). Nonshape-selective surface activity is observed on very small crystals, and it may be desirable to poison these sites selectively, eg, with bulky heterocycHc compounds unable to penetrate the channel apertures, or by surface sdation. 

Reverse osmosis models can be divided into three types irreversible thermodynamics models, such as Kedem-Katchalsky and Spiegler-Kedem models nonporous or homogeneous membrane models, such as the solution—diffusion (SD), solution—diffusion—imperfection, and extended solution—diffusion models and pore models, such as the finely porous, preferential sorption—capillary flow, and surface force—pore flow models. Charged RO membrane theories can be used to describe nanofiltration membranes, which are often negatively charged. Models such as Dorman exclusion and the... 

Several theories have appeared in the Hterature regarding the mechanism of protection by -PDA antiozonants. The scavenger theory states that the antiozonant diffuses to the surface and preferentially reacts with ozone, with the result that the mbber is not attacked until the antiozonant is exhausted (25,28,29). The protective film theory is similar, except that the ozone—antiozonant reaction products form a film on the surface that prevents attack (28). The relinking theory states that the antiozonant prevents scission of the ozonized mbber or recombines severed double bonds (14). A fourth theory states that the antiozonant reacts with the ozonized mbber or carbonyl oxide (3) in Pig. 1) to give a low molecular weight, inert self-healing film on the surface (3). 

The image-related transfer of a diffusible dye formed as a product of the oxidation of a dye containing a developing agent moiety was described in 1966 (32). This process depends on the preferential transfer of an oxidation product having greater mobility than the unoxidized species. Compound [13251 -03-1] (2), for example, a bis-sulfonjlhydrazide, upon oxidation releases [573-89-7] (3), a smaller, more mobile dye. 

In the case of TiC, preferential evaporation of titanium leads to a change in the stoichiometry of the compound towards the carbon-rich end, the excess carbon being left diffuses into the carbide phase, and so the flux ratio of the two elements changes widi time until congruent vaporization is achieved. 

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