Spatial heterogeneity network structure

Network structures have been quantitatively determined by means of real-time XH NMR T2 relaxation experiments for several polymers [174-178]. The effect of the curing conditions on sol and gel fractions and the spatial heterogeneity of the network structure has been studied for polyethylene [174], polyacrylamide [175], PDMS [176], BR [177], epoxy resins [178] and EPDM [179]. 

Overall it is considered that the spatially independent network models, whilst simpler, should strictly be used for lightly crosslinked, homogeneous networks, whereas the spahally dependent models, although computationally intensive and limited by pre-defined lattice structure, provide a better understanding of network heterogeneities in highly crosslinked systems. 

When the network structure of a gel is heterogeneous and the gel consists of small cells with microspace, the diffusion of the solvent is restricted spatially and will not follow Eq. (19). Thus, the observed diffusion coefficient reduces over time. Tanner [7] and Meerwall [18] studied such a limited diffusion using a model with parallel blocking walls with distance a and permeability p. They derived the relationship between the spin echo intensity A t) when the pulsed magnetic gradient with... 

In the new hierarchical structures of liquid crystal composite systems, this dynamic heterogeneity has a close relationship with the structure and dynamics of the composite. Even in the well-known micro-phase-separated structure of surfactants and in the mesoscale structures of polymer solutions, polymer blends, gels, and colloidal suspensions, molecular aggregates and polymer chain networks have a characteristic timescales, which are completely different from the surrounding medium, and thus static and dynamic spatial heterogeneity appears. 

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