Crosslink spatial distribution

Width of the transition. The a transitions are generally considerably sharper than secondary ones. The width of the a transition can be related to the degree of inhomogeneity of the spatial distribution of crosslink density (see Sec. 10.3.4). In contrast, secondary transitions can be considered intrinsically broad their width cannot be related to structural inhomogeneities. 

The recombination between two alkyl radicals is believed to be the main source of radiation-induced crosslinks in polyethylene [21], so that it is important to study the mechanism for formation and reaction of the alkyl radical. We have applied the ESE method to elucidate the paramagnetic relaxation mechanism and the spatial distribution of the alkyl radical, in order to get further insight into the radiation-chemical reactions of polyethylene resulting in the formation of crosslinks. 

The ion track radius is also an important parameter in such reactions, reflecting the local spatial distribution of energy deposited by an incident ion and influencing the character of subsequent chemical reactions [8-12]. We recently reported on main-chain scission and crosslinking reactions in a variety of polymer systems and proposed chemical core sizes in ion tracks based on discussion of the non-homogeneous spatial distribution of reactions [9-15]. Intratrack crosslinking reactions are also of interest with respect to the potential for the direct formation of nano-structured materials, and materials exhibiting these reactions have been successfully visualized in recent years [11,13]. However, despite the extensive experimental and theoretical study undertaken to date, many factors in the relationship between the ion track structure and the chemical core radius remain unclear. This paper proposes a new formulation that determines the chemical core radius in an ion track based on the initial... 

In this paper we report the application of the pCP technique to a functionalized alkanedisulphide - 11,11 -dithio-bis(succinimidyl-undecanoate) (DSU). We also describe a strategy for rendering etched silicon/gold structures accessible to this reactive crosslinker SAM. We subsequently present the site-specific immobilization of proteins onto such surfaces (Fig. 1) demonstrating the retained functionality of the immobilized protein. The atomic force microscope (AFM) was used to image the immobilized proteins and to determine their amount and spatial distribution on the patterned, template-stripped gold (TSG) surface. 

For the q range studied, the values for the bimodal networks are found to be similar to unimodal networks. The fact that the correlation size in a swollen network is much lager than in the corresponding semi-dilute solution is usually taken to be an indication of inhomogeneities in the network structure. However, the similarity of the results from the unimodal and bimodal networks seems to suggest that in the absence of non-random crosslinking, the distribution of crosslink densities is not the dominant factor in determining spatial correlations in a swollen network at the level of the network mesh size. 

In this section, several examples of studies on the evaluation of the gel point fi-om the viewpoint of the loss of sol fluidity have been introduced. The majority of these studies focused on the classification of the characteristics of the crosslink structure. In the future, the research focus will likely shift towards an interpretation and correlation of gel properties with respect to parts other than crosslinks and spatial distribution of crosslinks. 

Figure 4(a) shows the homogeneous network chains that possess equal molecular weight between crosslink points widi no distribution and whose crosslink points spatially distribute homogeneously. 

Measurements of soluble fractions, average molecular weights and molecular weight distributions enable yields of crosslinking and scission to be derived using appropriate equations. However, these relationships depend on assumptions which may not be valid, e.g. that the crosslinks are distributed spatially at random in the polymer. 

In principle, multivalent counterions can physically crosslink polyelectrolytes, which cause a further complication in the description of the joint conformational distribution of the polymer chain and spatial distribution of the counterions. While FS with its two spatially close charges may not be well suited to study this phenomenon, the larger trivalent counterion TAM (Figure 15) does crosslink PDADMAC." Unlike the nitroxide FS, the triphenylmethyl radical TAM is not amenable to DEER experiments, as its ESR spectmm is too narrow. On the other hand, the narrow spectmm opens up the possibility to estimate distance distributions from dipolar line broadening, in analogy to the related analysis of nitroxide spectra described in Sertion 2.08.2.4. To avoid distortions by electron-proton spin flip transitions, the experiments were performed at W-band frequencies. 

The latter result shows that to interpret the mechanical properties of networks we do not need to take into account the spatial inhomogeneities of crosslink distribution in a sample, at least in the rubbery state. The analysis of epoxy networks performed under the framework of a tree-like model and experiments 7,10-26) brought the... 

Tang et al. (2004) presented a cure model that captures transient, thermal and chemical effects that are ignored in typical threshold-based models. This new model incorporates as inputs photoinitiation rates, reaction rates, diffusion and temperature distributions, and is able to determine the spatial and temporal distributions of monomer and polymer concentrations, molar masses, crosslink densities and degree of cure. 

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