Immobilized network junctions

When the network junctions are entirely immobilized by the surrounding chains, h equals zero. Then the junctions in a deformed specimen are displaced in proportion to the macroscopic strain, i.e., the deformation is affine. Alternatively, h equals unity when junction fluctuations are not impeded, the defining characteristic of a phantom network (16, 17). The parameter h was introduced (13) to allow empirically for different degrees of fluctuations. For undiluted networks at small deformations, h should usually be small, though not necessarily zero. 

Finally, the NMR and the dynamic mechanical study show that two regions are present in filled silicone rubbers above the Tg, which differ significantly in local chain mobility immobilized chain units adsorbed at the filler surface and mobile chain units outside the adsorption layer. The local chain motions outside the adsorption layer are similar to those for unfilled rubbers. Chain motions in the adsorption layer however are strongly restricted. The frequency of chain motions in the adsorption layer at 300 K is comparable to the fi-equency of chain motions in a crosslinked PDMS containing 3-4 elementary chain units between network junctions [26]. 

Since the particles forming a fractal gel are reactive for aggregation over their total surface, the free energy of the system would decrease when the coordination number of the particles increases, or in other words when more junctions between particles would be formed. However, since the particles are more or less immobilized in the network, this is hardly possible, especially if the gel is constrained in a vessel and sticks to the vessel wall. However, if

Brownian motion), so that a new junction between particles may occasionally form. This causes tension in the strand(s)... 

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