Network inhomogeneities

Figure 12 shows the stress-strain curves of IER at various temperatures. A strain-induced reinforcing effect is not observed at temperatures above -10 °C. This fact may be due to network inhomogeneities caused by imperfect crosslinking. 

A concomitant of coil shrinkage would seem to be a macroscopic shrinkage of the gel structure, called syneresis, if the crosslinking were carried out in solution. Syneresis is indeed observed at the later stages of crosslinking in highly diluted systems [see Refs. (17) and (257) for examples]. Some evidence of localized network inhomogeneities has also been adduced in polycondensation networks... 

One possible way of characterizing the network inhomogeneity linked to spatial fluctuations of the crosslink density (Chapter 7) could be to study the width of the a dissipation band in the DMTA or DS spectra. The comparison between tetraglycidyl methylene dianiline (TGMDA) DDS... 

Compared to swelling-kinetic measurements DLS is a very fast method to determine D oop of gels. Information about the network inhomogeneity can be drawn additionally. 

Suspension polymerization as an additional source of network inhomogeneity... 

The molecular model of an elastomeric network with local intermolecular correlations, given by Flory, is used to calculate the components of the molecular deformation tensor and molecular orientation. Effects of molecTilar parameters such as severity of entanglements, network inhomogeneities and conditions during cross-linking are discussed. Components of molecular deformation and orientation are calculated for a network under uniaxial stress. 

In the case of perfect networks, combination of equations (47), (107), (112) and (113) yields equation (124). Thus, k depends on the inverse square-root of the phantom modulus and is independent of swelling. The factor is Avogadro s number, which appears in equation (124) since n in equation (112) is the number of junctions and not the number of moles of junctions. In the case of randomly cross-linked networks, use of equation (61) yields equation (125). In the case of networks formed by random cross-linking of star polymers, equation (63) is used instead of equation (61) to derive the expression for k. The other parameter C is the result of the relationship between k and network inhomogeneities and its magnitude is estimated by experiment. 

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