Interfadal activity

Chan, M. Yen, T.F. A Chemical Equilibrium Model for Interfadal Activity of Crude Oil in Aqueous Alkaline Solution The Effects of pH, Alkali and Salt, Canadian J. Chem. Eng. 1982, 60, 305. 

Other interfadally active species at polymer/polymer interfaces... 

The interfadal activity of amphiphiles is but one manifestation of their discordant intramolecular makeup. These molecules can also self-assemble in solution to form a variety of microstructures, such as micelles and vesicles to name a few. Of course structures based on a bilayer motif, such as vesicles, have direct biological relevance as they serve as models for cell membranes. 

Tlie observed contraction dynamics of the P2VP chains on mica in ethanol vapor was explained in the framework of the spreading concept. Hie amphiphilic ethanol solvent molecules exhibit a higher interfadal activity as compared to the polymer molecules. Hierefore, coadsorbtion of an ethanol... 

Singh et al. ( i) postulated that asphaltenes stabilize w/o emulsions in two steps. First, disklike asphaltenes molecules aggregate into particles or micelles, which are interfadally active. Then, these entities upon adsorbing at the w/o interface aggregate through physical interactions and form an interfacial network. Different modes of action of asphaltenes are represented in Figure 12. 

There are many published examples in which the coupling of two different materials leads to an increase in the photocatalytic activity. Many of them concern coupling and junctions between different nanopartides, considering also different topologies, like coupled and capped systems [72]. Tentative explanations based on possible heterojunction band profiles are given. However, in-depth analysis of the hetero junction band alignment, the physical structure of the junction, the role of (possible) interfadal traps and of spedfic catalytic properties of the material is still lacking. Some recently published models and concepts based on (nano)junction between different materials are briefly reviewed here. 

In the active state, the dissolution of metals proceeds through the anodic transfer of metal ions across the compact electric double layer at the interface between the bare metal and the aqueous solution. In the passive state, the formation of a thin passive oxide film causes the interfadal structure to change from a simple metal/solution interface to a three-phase structure composed of the metal/fUm interface, a thin film layer, and the film/solution interface [Sato, 1976, 1990]. The rate of metal dissolution in the passive state, then, is controlled by the transfer rate of metal ions across the film/solution interface (the dissolution rate of a passive semiconductor oxide film) this rate is a function of the potential across the film/solution interface. Since the potential across the film/solution interface is constant in the stationary state of the passive oxide film (in the state of band edge level pinning), the rate of the film dissolution is independent of the electrode potential in the range of potential of the passive state. In the transpassive state, however, the potential across the film/solution interface becomes dependent on the electrode potential (in the state of Fermi level pinning), and the dissolution of the thin transpassive film depends on the electrode potential as described in Sec. 11.4.2. 

In the aqueous biphasic hydroformylation reaction, the site of the reaction has been much discussed (and contested) and is dependent on reaction conditions (temperature, partial pressure of gas, stirring, use of additives) and reaction partners (type of alkene) [35, 36]. It has been suggested that the positive effects of cosolvents indicate that the bulk of the aqueous liquid phase is the reaction site. By contrasL the addition of surfactants or other surface- or micelle-active compounds accelerates the reaction, which apparently indicates that the reaction occurs at the interfadal layer. 

The first attempts of Bidlingmeyer and co-workers [15,16] to formulate an ion interaction model quantitatively [21-23] did not provide a rigorous description of the system. Stranahan and Deming [22] accounted for electrostatic effects via a simplified activity coefficient in the stationary phase. An interfadal tension decrease with increasing IPR concentration was considered responsible for the appearance of maxima in the plot of retention factor, k versus IPR concentration, but experimental results were at odds with known surfactant chemistry. 

Interfadal tension, however, cannot serve as the only criterion of adsorption. Typical sui ctants with asymmetric molecules or ions consisting of a polar group and a sufficiently long hydrocarbon chain are always active at water-hydrocarbon interfaces. The greater the difference in polarity between bounda ry phases the steeper the orientation of surfactant molecule at the interface and the larger the reduction in free energy of the system due to adsorption. 

The second approach was based on monitoring the interfadal characteristics of surfactant solutions kept at reservoir temperature. Foaming capacity was chosen as a measure of surfactant interfacial activity, and all nine surfactants followed the pattern shown in Figure 1 and indicated no deterioration over time. 

Surfactant Any substance that lowers the surface or interfacial tension of the medium in which it is dissolved. The substance does not have to be completely soluble and may lower surface or interfadal tension by spreading over the interface. Soaps (fatty acid salts containing at least eight carbon atoms) are surfactants. Detergents are surfactants or surfactant mixtures whose solutions have cleaning properties. Also referred to as surface-active agents or tensides. 

The signal-triggered functions of these molecular assemblies have to be first characterized in bulk solution. Then, extensive efforts have been directed to integrate these photoswitchable chemical assemblies with transducers in order to tailor switchable molecular devices. The redox properties of photoisomerizable mono-layers assembled on an electrode surface are employed for controlling interfadal electron transfer [16]. Specifically, electrical transduction of photonic information recorded by photosensitive monolayers on electrode supports can be used in developing monolayer optoelectronic systems [16-19]. Electrodes with receptor sites exhibiting controlled binding of photoisomerizable redox-active substrates from the solution [20] also allow the construction of molecular optoelectronic devices. 

Rosenbauer E-M, Landfester K, Musyanovych A (2009) Surface-active monomer as a stabilizer for polyurea nanocapsules synthesized via interfadal polyaddition in inverse miniemulsion. Langmuir http //dx.doi.oig/10.1021/la9017097... 

Sundmacher and Qi (Chapter 5) discuss the role of chemical reaction kinetics on steady-state process behavior. First, they illustrate the importance of reaction kinetics for RD design considering ideal binary reactive mixtures. Then the feasible products of kinetically controlled catalytic distillation processes are analyzed based on residue curve maps. Ideal ternary as well as non-ideal systems are investigated including recent results on reaction systems that exhibit liquid-phase splitting. Recent results on the role of interfadal mass-transfer resistances on the attainable top and bottom products of RD processes are discussed. The third section of this contribution is dedicated to the determination and analysis of chemical reaction rates obtained with heterogeneous catalysts used in RD processes. The use of activity-based rate expressions is recommended for adequate and consistent description of reaction microkinetics. Since particles on the millimeter scale are used as catalysts, internal mass-transport resistances can play an important role in catalytic distillation processes. This is illustrated using the syntheses of the fuel ethers MTBE, TAME, and ETBE as important industrial examples. 

Two-dimensional (2D) phase transitions on surfaces or in adlayers have received increased attention in recent years [1-4] as they are related to important aspects in surface, interfadal and materials science, and nanotechnology, such as ordered adsorption, island nucleation and growth [2, 5-7], surface reconstruction [8], and molecular electronics [9], Kinetic phenomena such as catalytic activity and chirality of surfaces [10-12], selective recognition of molecular functions [13], or oscillating chemical reactions [14] are directly related to phase-formation processes at interfaces. 

The ability of surface-active agents to adsorb on solid-liquid interfaces and produce a modihcaiion of the interfadal properties depends on the chemical nature of the three mutually interacting components of the system the substrate, solid particles the adsorbate, surfactant molecules and the liquid medium, usually an aqueous. solution. If the nature of the solid substrate is nonpolar, then the adsorption takes place by dispersion force interactions. The orientation of the adsorbed molecules is such that the hydrophobic groups of the chain become associated... 

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