Surface chain diffusion

When compared to the early models that describe the adhesion of elastomers in the presence of interfacial chains, the central findings of this work, namely, observations b and d above, were quite surprising. In his recent work, de Gennes [102] pointed out that when a surface tethered chain diffuses into an elastomeric... 

Radical Desorption Rate. It is evaluated, according to the law proposed by Nonura (36), as the result of three stages in series Chain transfer of a growing chain to monomer, diffusion of the active, low molecular weight product to the particle surface and diffusion in the aqueous phase. The resulting expression has been extended to the multlconponent case as follows ... 

It should be evident from this discussion that the first explosion limit will be quite sensitive to the nature of the surface of the reaction vessel and its area. If the surface is coated with a material that inhibits the surface chain termination process, the first explosion limit will be lowered. Inert foreign gases can also have the effect of lowering the first explosion limit, since they can hinder diffusion to the surface. If something like spun glass or large amounts of fine wire are inserted, one can effect an increase in the first explosion limit by changing the surface/ volume ratio of the system. 

CHX and hydrocarbon wax are, respectively, the active intermediates formed by the hydrogenation of surface carbide and products of FTS formed by chain growth and hydrogenation of CHX intermediates. The hydrocarbon wax can contain molecules with the number of carbon atoms in excess of 100. Bulk carbide refers to a crystalline CoxC structure formed by the diffusion of carbon into bulk metal. Subsurface carbon may be a precursor to these bulk species and is formed when surface carbon diffuses into an octahedral position under the first surface layer of cobalt atoms. 

Consolidation and development of interlaminar bond strength for thermoplastic matrix composites have been modeled by two mechanisms intimate contact and autohesion. Intimate contact describes the process by which two irregular ply surfaces become smooth (Fig. 13.10). In areas in which the ply surfaces are in contact, autohesion occurs, and the long thermoplastic polymer chains diffuse across the ply boundaries. Filament winding with thermoplastic matrix materials is considered an on-line consolidation process in that local... 

If we assume, for concreteness, that chain initiation occurs by chains starting at the surface and diffusing out into the gas where branching takes place and that termination occurs by diffusing back to the sih face, then the condition that governs radical concentration may be expressed by the quasi-stationary-state condition... 

In general, during CVD growth, the rate of polymer chain propagation exceeds those of initiation and termination and is a strong function of the substrate temperature. This rate varies inversely with substrate temperature, i.e., decreases with increasing substrate temperature and vice versa. As mentioned earlier, chemical reactions on the surface, lateral diffusion of the incoming species, vaporization, are all characterized by activation processes and obey an Arrhenius temperature dependence of the form ... 

Yoon, Smith, and Matsuda, on the other hand, compared two approaches, using a united-atom model and a fully atomistic model.Stochastic dynamics and MD simulations of w-tridecane (C13H28) were used to study polyethylene. Besides studying the bulk melt, the authors examined confined melts between solid surfaces. Chain conformations, chain packing orientational correlations, and self-diffusion were among the properties studied. In regard to chain confer-... 

Higher intrapellet residence times increase the contribution of chain initiation by a-olefins to chain growth pathways. This intrapellet delay, caused by the slow diffusion of large hydrocarbons, leads to non-Flory carbon number distributions and to increasingly paraffinic long hydrocarbon chains during FT synthesis. But intrapellet residence time also depends on the effective diameter and on the physical structure (porosity and tortuosity) of the support pellets. The severity of transport restrictions and the probability that a-olefins initiate a surface chain as they diffuse out of a pellet also de-... 

Indeed, plausible explanations of the effects of halogen and Mg/RX in terms of the proposed surface chain mechanism are not obvious. According to this mechanism, the lifetime of R-. and therefore the extent to which it cyclizes, will be halogen-independent, contrary to observation. Also, if the intermediates remain at the surface, the same mechanism predicts that the product distribution will be independent of the area of Mgz (Section 7.2.13). The observed effects suggest that intermediates diffuse in solution. 

Compared with that in the conventional supercritical phase reaction, the carbon chain growth was accelerated by the addition of alkenes with long carbon chains into the accompanying fluid. The essential prerequisite for this process is the rapid diffusion of these heavy added alkenes inside the catalyst pores to reach the metal sites, as well as effective diffusion of the heavy products produced from the interior active sites to the outer catalyst surface. Both diffusion processes are readily achieved in the supercritical phase. 

The electrochemical oxidation of thiophene and its derivatives forms part of a recent exhaustive review of such oxidations of several heteroaromatic compounds <86CJC76>. The mechanism has been explained. The initially formed radical cation is sufficiently stable to dimerize, but not so stable as to diffuse away from the electrode surface. Chain propagation takes place by coupling of the monomer radical cation with the dimer radical cation and so on. Cyclic voltammetric data for thiophene and its derivatives have been provided. 

Therefore, the current strategy is based on an even more complex architecture of the micro-network. Alter formation of the PDMS-containing micro-emulsion a thin shell of a functionalized monomer (e.g. />-chloromethylphenyltrimethoxysilane) is formed, followed by a second elastomeric shell of trimethoxymethylsilane and dimethoxydimethylsilane. Again, the linear PDMS chains diffuse out of the micro-network. So far, the experiments are successfully completed. Future work comprises the reaction of p-chloromethylphenyltrimethoxysilane, which is exclusively located at the inner rim of the hollow micro-networks, with trimethylamine, which will hydrophilically modify the inner surface by formation of ionic ammonium groups. This last step has not yet been... 

More recently, it has been pointed out that aged gels possess self-healing properties at room temperature, without the need for any stimulus or healing agent [10]. Welding occurs spontaneously via chain diffusion across the interface provided that a sufficient number of PVA free hydroxyl groups survive at the contact between the two cut surfaces [10]. 

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