Polymers cluster deposition

Figure 9 (a) TEM image of a cutout of hexagonally ordered AussfPPhsinCle clusters, deposited on a polymer film. (Ref. 56. Reproduced by permission of Wiley-VCH). (b) Magnified cutout... 

Chemical alternation of the surface layer and deposition of a new layer on top of the silicone mbber can be achieved by physical techniques. For the inert surface of silicone rubber, the former requires the generation of high-energy species, such as radicals, ions, or molecules in excited electronic states. In the latter case, coatings of atoms or atomic clusters are deposited on polymer surfaces using technique such as plasma (sputtering and plasma polymerization) or energy-induced sublimation, like thermal or electron beam-induced evaporation. 

Deposition of Cold Nanoparticles and Clusters onto Carbons and Polymers 3.2.2.1 Cold Colloid Immobilization (Cl)... 

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. 

A second method of tip-directed synthesis involves a two-electrode STM configuration to form small clusters of metals, polymers, and semiconductors on graphite surfaces immersed in a dilute electrolyte [13,532-535]. Initially, the material to be deposited (i.e., Ag) is concentrated by... 

Type 3 metal complexes involve the physical interaction of a metal complex, chelates, or metal cluster with an organic polymer or inorganic high molecular weight compound. The preparation of type 3 compounds differs from those of type 1 and type 2, as they are ultimately achieved through the use of adsorption, deposition by evaporation, microencapsulation, and various other methods. 

The novel cluster-like chalcogenide material RuxSey deposited in thin [5, 26, 31, 36] and ultra-thin layers [9, 11] or in powder form embedded in a polymer matrix [30] was found to be an efficient catalyst for the molecular oxygen reduction in acid medium. Fig. 5.10 summarizes the current-potential (j-E) characteristics as a function of the substrate s nature. First of all, one can appreciate that similar activities are obtained from materials synthesized in powder or in colloidal form when deposited onto GC (Fig. 5.10, compare curves (1) and (2)). For the sake of comparison, the j-E characteristic generated on the naked GC substrate for the electrochemical process is contrasted in curve (5). 

On the other hand, to eliminate the electrocatalytic activity of the continuous donor clusters, use could be made of the blockage of their surface by the deposition of dielectric polymers such as poly-o-phenylenediamine [104]. It has been shown that the cycling of the anodic potential of WO3 films in the solution of o-phenylenediamine leads to a drastic decrease in the dark current caused by the selective deposition of dielectric polymer (Fig.6.17) This decrease is also accompanied by the changes in impedance characteristics and in other parameters [104],... 

Coagulation Catalyst preparation cluster and polymer formation in chemical vapor deposition intermolecular interactions between particles diffusion-limited aggregation soot formation. 

Alternatively PAA can be obtained without solvent by vapor deposition polymerization as described first by Salem et al. [2], In this technique the dianhydride py-romellitic and the dianhydride diamine (4,4 -oxidianiline) are codeposited onto a substrate, where they react to form PAA. Again the transformation to Polyimide is obtained by subsequent heating to temperatures up to 350°C. By comparison to spun dn films, initial interaction of the polymer with the substrate occurs in the uncomplexed PAA state. The chemical interaction between PAA and the metal establishes the adhesion of the final polyimide film. This is discussed in this communication for evaporated gold cluster and bulk silver surfaces. 

Spherical precipitates in the skin of a polymer have previously been observed after the evaporation of Cu on polyimide(PI)(liD- These two systems [Al/PET(sample(l)) and Cu/PI] present a low chemical interaction and a low adhesion, but the deposition rate was much lower for Cu/PI than for Al/PET (1 ML/mn compared with 50 nm/s). This behaviour has been interpreted by Le Goues and alfl 01 as a consequence of a poor chemical interaction between the metal and the polymer at the interface the metal being free to diffuse in the polymer to form clusters of nearly spherical shape. However, it is difficult to compare the mechanism of formation of these precipitates because of the huge evaporation rate difference this rate seems to be critical (Le Goues and al(l Oil for the formation of these precipitates. The presence of these precipitates can only be considered as a fingerprint of a poor quality interface. 

Other approaches to reducing the membrane pore size are being investigated. Many of them are based on the sol-gel process or chemical vapor deposition as discussed in Chapter 3. An example is the preparation of small-pore silica membranes. Amorphous silica membranes have been prepared from solutions of silicate-based polymers. More specifically, some strategies are employed aggregation of fractal polymeric clusters, variation of sol composition, the use of organic molecular templates and modification of pore surface chemistry [Wallace and Brinker, 1993]. 

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