Phase-growth mechanism

Although the mechanisms discussed above are still topics of debate, it is now firmly established that the electrodeposition of conducting polymers proceeds via some kind of nucleation and phase-growth mechanism, akin to the electrodeposition of metals.56,72-74 Both cyclic voltammetry and potential step techniques have been widely used to investigate these processes, and the electrochemical observations have been supported by various types of spectroscopy62,75-78 and microscopy.78-80... 

These and other results have been used to formulate a mechanism of the formation of boron nitride in the SHS wave [26, 31], which is based on the concept of crystal growth by the vapor-liquid-crystal (VLC) mechanism. Indeed, the sudden change in the morphology of the medium - from submicron spherical boron particles to 20 pm plates of the nitride at temperatures below the melting point of boron - indicates the gas phase growth mechanism of the BN crystals, as the... 

The first concept, the formation of a template layer, is suggested to enhance adsorption of the first monomer onto the surface as a single monolayer. A template layer is a self-assembled monolayer deposited fi om solution, which exposes a reactive functionality toward the first monomer, prior to introduction of the substrates to vapor phase assembly. This template layer dictate epitaxial growth and ensure the second concept of self-limiting growth of only one monolayer. Therefore, this layer bridges solution and vapor phase growth mechanisms in a unified concept... 

Chain-Growth Associative Thickeners. Preparation of hydrophobically modified, water-soluble polymer in aqueous media by a chain-growth mechanism presents a unique challenge in that the hydrophobically modified monomers are surface active and form micelles (50). Although the initiation and propagation occurs primarily in the aqueous phase, when the propagating radical enters the micelle the hydrophobically modified monomers then polymerize in blocks. In addition, the hydrophobically modified monomer possesses a different reactivity ratio (42) than the unmodified monomer, and the composition of the polymer chain therefore varies considerably with conversion (57). The most extensively studied monomer of this class has been acrylamide, but there have been others such as the modification of PVAlc. Pyridine (58) was one of the first chain-growth polymers to be hydrophobically modified. This modification is a post-polymerization alkylation reaction and produces a random distribution of hydrophobic units. 

M. Endo. Meeanisme de eroissanee en phase vapeur de fibres de earhone (Tlte growth mechanism of vapor-grown carbon fibers). PhD thesis. University of Orleans, Orleans, France, 1975. (in French). 

The growth pathway of various fullerene- and graphene-type nano-objects may be related. They are synthesized in the vapor phase and often appear simultaneously on the same sample. A common growth mechanism with similar nucleation seeds may, therefore, lead to these different structures. 

The most important nanomaterial synthesis methods include nanolithography techniques, template-directed syntheses, vapor-phase methods, vapor-liquid-solid (VLS) methods, solution-liquid-solid (SLS) approaches, sol-gel processes, micelle, vapor deposition, solvothermal methods, and pyrolysis methods [1, 2]. For many of these procedures, the control of size and shape, the flexibility in the materials that can be synthesized, and the potential for scaling up, are the main limitations. In general, the understanding of the growth mechanism of any as-... 

These are normally prepared by a step growth mechanism. They can be thermoplastic or thermoset and are often used in composites. Composites are materials that contain two or more phases, one of which acts as a reinforcement... 

The most industrially significant polymerizations involving the cationic chain growth mechanism are the various polymerizations and copolymerizations of isobutylene. In fact, about 500 million pounds of butyl rubber, a copolymer of isobutylene with small amounts of isoprene, are produced annually in the United States via cationic polymerization [126]. The necessity of using toxic chlorinated hydrocarbon solvents such as dichloromethane or methyl chloride as well as the need to conduct these polymerizations at very low temperatures constitute two major drawbacks to the current industrial method for polymerizing isobutylene which may be solved through the use of C02 as the continuous phase. 

Proposed Growth Models. Summarizing the results given above, the growth mechanisms are proposed as follows. Because of the location of nanoparticles at the tips of SiNW, we conclude that growth must occur in the gas phase. More precisely, we think that Co silicide SAN play a role here. They help convert Si and H2 into SiH4 (gas). Unreacted Co nanoparticles left on the surface, possibly due to the... 

A. Persson, M. Larsson, S. Stenstrom, B. Ohlsson, L. Samuelson, and L. Wallenberg, Solid-phase diffusion mechanism for GaAs nanowire growth. Nature Mater. 3, 677-681 (2004). 

Despite the vast quantity of data on electropolymerization, relatively little is known about the processes involved in the deposition of oligomers (polymers) on the electrode, that is, the heterogeneous phase transition. Research - voltammetric, potential, and current step experiments - has concentrated largely on the induction stage of film formation of PPy [6, 51], PTh [21, 52], and PANI [53]. In all these studies, it has been overlooked that electropolymerization is not comparable with the electrocrystallization of inorganic metallic phases and oxide films [54]. Thus, two-or three-dimensional growth mechanisms have been postulated on the basis that the initial deposition steps involve one- or two-electron transfers of a soluted species and the subsequent formation of ad-molecules at the electrode surface, which may form clusters and nuclei through surface diffusion. These phenomena are still unresolved. 

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