Mechanism interfacial

The interfacial mechanism refers to the microcosmic mechanism of the interface function. Generally, the resin phase is in solution or melt flow state to contact with the filler to form composite materials after a curing reaction or cooling curing. In this process, how the resin interacts with the filler becomes of more and more concern. 

A variety of interface function theories of composite materials have been proposed, but none is completely adequate. The following are current relatively popular and important theories. 

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These results clearly show that microwave electrochemical techniques are providing valuable new insights into the kinetics of relevant interfacial mechanisms. 

In some cases, the Q ions have such a low solubility in water that virtually all remain in the organic phase. ° In such cases, the exchange of ions (equilibrium 3) takes place across the interface. Still another mechanism the interfacial mechanism) can operate where OH extracts a proton from an organic substrate. In this mechanism, the OH ions remain in the aqueous phase and the substrate in the organic phase the deprotonation takes place at the interface. Thermal stability of the quaternary ammonium salt is a problem, limiting the use of some catalysts. The trialkylacyl ammonium halide 95 is thermally stable, however, even at high reaction temperatures." The use of molten quaternary ammonium salts as ionic reaction media for substitution reactions has also been reported. " " ... 

SCHEME 3 Interfacial mechanism in the ion-association extraction of Fe(II) with phen or its derivatives (L) including an anion X. 

The automatic measurement of the extracellular and intracellular electrical potential difference can be effectively used in plant electrophysiology for studying the molecular interfacial mechanisms of ion transport, the influence of external stimuli on plants, and for investigating the bioelectrochemical aspects of the interaction between insects and plants. 

An issue as interesting as it is contentious is that of electrolyte inhibition of bubble coalescence. Recently, a number of studies have reported the ion-specific nature of electrolyte inhibition of bubble coalescence, albeit in static (non-acoustic) fields [43 -9]. Some electrolytes appear to be highly efficacious whereas others almost completely ineffectual in inhibiting coalescence and ion combination rules have been devised to predict the behavior of various ion pairs. Various explanations have been proposed, most implying a gas-liquid interfacial mechanism. Christenson and Yaminsky [44] have reported a correlation between the inverse Marangoni factor, (dy/ dc]) 2, and coalescence inhibition ability for several different... 

However, the observation that very organophilic ammonium salts are also very active phase transfer agents suggests that the catalyst cation need not actually enter the aqueous phase, and the reaction can occur entirely at the interface, as depicted in Scheme 5.7 [43], This process is known as the interfacial mechanism. 

Scheme 5.7 Interfacial mechanism for simple anion displacement. In PTC, Q+ is resident in the organic phase and draws the anion across the interface...

Ho, H. and Drzal, L. T., Evaluation of interfacial mechanical properties of fiber reinforced composites using the microindentation method, Composites, A, 27, 961 (1996). 

The interfacial mechanism probably competes to some extent with the extraction mechanism, particularly with the less lipophilic catalysts. The dependence of the rate of many nucleophilic substitution reactions on the stirring rate up to 250-300 rpm and the independence of the reaction rate at higher stirring rates has been taken as evidence for a change over from a predominant interfacial mechanism to an extraction process. The interfacial mechanism is also particularly relevant to base-initiated reactions. 

The interfacial mechanism provides an acceptable explanation for the effect of the more lipophilic quaternary ammonium salts, such as tetra-n-butylammonium salts, Aliquat 336 and Adogen 464, on the majority of base-initiated nucleophilic substitution reactions which require the initial deprotonation of the substrate. Subsequent to the interfacial deprotonation of the methylene system, for example the soft quaternary ammonium cation preferentially forms a stable ion-pair with the soft carbanion, rather than with the hard hydroxide anion (Scheme 1.8). Strong evidence for the competing interface mechanism comes from the observation that, even in the absence of a catalyst, phenylacetonitrile is alkylated under two-phase conditions using concentrated sodium hydroxide [51],... 

As an alternative to the extraction and interfacial mechanisms, hydroxide promoted dehydrohalogenation reactions may also occur, not by proton removal from the... 

The acidity of amides (pKa 23) is such that it is reasonable to postulate that, in contrast with the analogous reactions of the amines, the phase-transfer catalysed N-alkylation proceeds by way of the initial generation of the amidic anion under basic conditions. It has been demonstrated that the preformed sodium salt of benzamide can be solubilized in toluene upon the addition of Aliquat [1 ] and further evidence [2] has been provided for the postulated deprotonation under the two-phase conditions in which it is assumed that the deprotonation occurs by an interfacial mechanism (see Chapter 1). 

As indicated in Chapter 1, the hydroxide ion is not readily transported into the organic phase, particularly when the benzyltriethylammonium ion is employed as the catalytic cation. Hence, the reaction of chloroform with the hydroxide ion must occur by an interfacial mechanism. The interfacial reaction initially produces the trichloromethyl anion, which immediately forms an effective ion-pair with the benzyltriethylammonium cation. Diffusion of the ion-pair into the bulk of the organic phase occurs, followed by a slow decomposition of the trichloromethyl anion... 

A question of ufmosf inferesf is whefher high proton mobility in aqueous-based PEMs is possible under conditions of minimal hydration and at elevated temperature. Obviously, the answer could have a tremendous impact on promising design strategies in membrane research. - ° This calls attention to interfacial mechanisms of proton transport (PT). 

Ferber, M.K., Wereszczak, A.A., Hansen, D.H. and Homeay, J. (1993). Evaluation of interfacial mechanical properties in SiC fiber-reinforced macro-defect-free cement composites. Composites Sci. Technol. 49, 23-33. 

Marshall, D.B. and Oliver, W.C. (1987). Measurement of interfacial mechanical properties in fiber-reinforced ceramic composites. J. Am. Ceram. Soc. 70, 542 548. 

The stirred cell of Davies (11) was used to investigate the possible interfacial mechanism of extraction. Transfer of the complex Hs PbSCSN Hs from the aqueous to the organic phase was studied as a function of the stirring rate in the aqueous phase. 

We have used a multiple approach in trying to establish interfacial mechanisms and structures pertaining to the interaction of Ca++ with films of DPL. 

The exact pathway for generating the reactive onium carbanion species remains the subject of controversy, typically among Starks extraction mechanism (Scheme 1.2) and the Makosza interfacial mechanism (Scheme 1.3). 

The advocated pathway of the interfacial mechanism is the first formation of metal carbanion at the interface of organic and aqueous phase in the absence of phase-transfer catalyst, followed by the extraction of the formed metal carbanion species from the interface into the organic phase by the action of phase-transfer catalyst. 

Since asymmetric phase-transfer catalysts normally contain highly lipophilic chiral organic frameworks, and are reluctant to enter the aqueous phase, the Makosza interfacial mechanism seems plausible. 

With regards to the mechanism of the generation of onium anion, the Starks extraction mechanism and interfacial mechanism (Brandstrom-Montanari modification) are suggested (Scheme 1.7). As in the above-described case, the interfacial mechanism seems to be operative in the asymmetric phase-transfer catalysis. 

A. C. Ross, G. Bell, and P. J. Halling, Organic solvent functional group effect on enzyme inactivation by the interfacial mechanism, J. Mol. Cat. B Enzymatic 2000, 8, 183-192. 

Figure 4.28 Different pathways for PTC a the classic Starks extraction mechanism b the Makosza interfacial mechanism.

Scheme I. Interfacial mechanism of solvent extraction of metal ion (M2+).

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