Surface-induced decomposition

As outlined in Section 2.2.4.1, impurities and catalysts may decrease To significantly a decrease of 100°C is not unusual. The material of construction of the sample cup may act as a catalyst, resulting in surface-induced decomposition which may even be promoted by the sample/surface area ratio in the DSC cup. Therefore, it is important to check if the substance is catalyzed during the DSC experiment and if such catalysis is representative of process conditions. Frequently, substances that are sensitive to catalysis are handled in passivated glass-lined reactors, receptacles, or containers. Another phenomenon to recognize is autocatalytic decomposition. Substances that are susceptible to autocatalytic decomposition have an induction period prior to initiation of rapid decomposition. The same holds for substances that contain inhibitors, which can be depleted. 

SFC/MS. supercritical fluid chromatography and mass spectrometry used as a combined technique SID. surface-induced dissociation (or decomposition)... 

Supramolecular chemistry on crystalline surfaces is governed to a large extent by lateral interactions. Nevertheless, the substrate plays an important role in mediating these interactions. Intermolecular recognition on a surface, for example, can take place only if the adsorbate-substrate interaction allows the molecules to meet each other. Therefore, the choice of the substrate plays a decisive role. Too strong interactions immobilize molecules and do not leave room for 2D supramolecular chemistry or may even induce decomposition too weak adsorbate-substrate interactions cause high mobility and 2D crystallization phenomena will not occur. 

Formation of protecting surface layer before or after ignition being in competition with the heat-induced decomposition of the polymer chains and oxidation of the formed fragments by radical process... 

Perhaps the most compelling evidence for the X-ray induced decomposition of bulk layers of TDF is the fact that a substantial amount of TDF-derived features remained on the surface after the same X-ray irradiated specimen was warmed to room temperature (see curves 3, Figure 7). This behavior is unlike that observed for TDF films condensed on clean Ag and not exposed to the X-ray beam until after the specimen had been heated to ca. 300 K by flowing hot N2 through the cryostat (vide infra), in which case clean Ag was obtained. 

Knotek and Feibelman [94] examined the modification to a surface when exposed to ionising radiation and assesed the damage that can be produced. They addressed the stability of ionically bonded surfaces, where the KF mechanism applies, and concluded that Auger induced decomposition only occurs when the cation in the solid is ionised to relatively deep core levels. In the case of non-maximal oxides as with NiO, Freund s group [95] showed that whilst desorption of neutral NO and CO from NiO(lOO) and (111) surfaces has thresholds at the C Is, N Is and O Is core levels, it proceeds mainly on the basis of the MGR model, involving an excited state of the adsorbate. An overview of electronic desorption presented by Feibelman in 1983 [96] examined particularly the stability of the multiple-hole final state configuration leading to desorption. The presence of multiple holes, and associated hole-hole correlation... 

If so, one may expect products to result from chemical bond formation between the cation-radical-anion-radical pair, which are both paramagnetic and of opposite charge. In the latter route, there is a precedent for the formation of dioxetane intermediates of stable olefin cation radicals [51], as in the characterization by Nelsen and coworkers of a dioxetane cation radical from adamantylidene cation radical [52]. If a dioxetane is formed, either in neutral form or as a cation radical, the Ti02 surface can function in an additional role, that is, as a Lewis acid catalyst, to induce decomposition of the dioxetane. Since no chemiluminescence could be observed in these reactions, apparently Lewis acid catalysis provides a nonradiative route for cleavage of this high-energy intermediate. That Ti02 can indeed function in this way can be demonstrated by independent synthesis of the dioxetane derived from 1,1-diphenylethylene, which does indeed decompose to benzophenone when it is stirred in the dark on titanium dioxide. 

Surface Induced Spinodal Decomposition Leading to Layered Coexisting Phases... 

The variation of the chemical composition of the substrate (not realized in a continuous tunable fashion) leads to drastic modifications of surface fields exerted by the polymer/substrate (i.e.,II) interface [94,97, 111, 114,119]. The substrate may, for instance, change contact angles with the blend phase from zero to a finite value. As a result the final morphology changes from a layered structure of Fig. 5b into a column structure of Fig. 5c [94,114]. On the other hand our very recent experiment [16] has shown that the surface fields are temperature dependent. Therefore, although it has been shown that surface-induced spinodal decomposition yields coexisting bilayer structure (Fig. 5b) at a singular temperature [114,115], that in principle may not be necessary true for other temperatures. This motivated our comparative studies [107] on coexistence compositions determined with two techniques described above interfacial relaxation and spinodal decomposition. 

Surface induced spinodal decomposition leads, for properly controlled surface fields, to a two layer structure characteristic for coexisting phases. Hence it may be used to determine the coexisting conditions in a more convenient way that with the interfacial relaxation method as the initial bilayer geometry may be avoided. In practical terms the overall composition of the whole thin film may be much better controlled in experiments involving spinodal decomposition. Therefore in experiments studying the equilibrium composition vs depth pro-... 

Coexistence conditions of high polymer mixtures may be determined directly with the advent of the novel approach [74,75] focused on two coexisting phases confined in a thin film geometry and forming a bilayer morphology. Such equilibrium situation is obtained in the course of relaxation of an interface between pure blend components or in late stages of surface induced spinodal decomposition. It is shown that both methods lead to equivalent results [107] (Sect. 2.2.1). 

The determination of the conformational and segregation properties of polymer brushes, created by diblock copolymers, has triggered their application to more complex problems. Diblock copolymers have been used to increase adhesion [277] or to eliminate the interfacial tension [256] between immiscible polymers. They may also modify the surface induced mode [116] and the bulk mode [278] of the spinodal decomposition observed in homopolymer blends. 

Fig. 37 Schematic diagram of laser-induced decomposition and ablation dynamics of the photosensitive triazene polymer film (a) before excimer laser irradiation, (b) slight expansion of the film and darkening of the irradiated surface at the beginning of the excimer laser pulse, (c) initiation of etching of the film and ejection of gaseous fragments decomposed from the polymer, (d) completion of the etching and expansion of ejected plume, and (e) after the ablation. REPRINTED WITH PERMISSION OF [Ref. 125], COPYRIGHT (1997) American Chemical Society...

In summary, mass-selected TOF measurements during the UV laser (248 nm)-induced decomposition of a photolabile polymer show fast neutral particles which are most likely due to particles emitted directly from the surface by a concerted, exothermal chemical reaction. At this point, time-of-flight measurements cannot distinguish whether this reaction is initiated directly by photon absorption (photochemical dissociation) or exothermic de-... 

The XeCl laser (308 nm)-induced decomposition of Kapton is studied to identify reaction steps leading to the previously mentioned gaseous products, and to identify the intermediate steps of the surface carbonization of Kapton. The XeCl laser is applied in the industrial processing of polyimide due to the reliability of its optical and laser components at the emission... 

We first present results of probe hole measurements on the stepped surface in the vicinity of the (001) pole of a Ru emitter tip. Next we compare these results with those obtained for the stepped region close to the (001) pole of a Pt emitter. Results of the field induced decomposition of NO over stepped Pt(111) will be reported. 

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