Interpretation of segmental orientation in deformed networks in terms of constrained junction model of rubber elasticity

Results of Fourier transform infra-red (FTi.r.) dichroism measurements of segmental orientation in model poly(dimethylsiloxane) (PDMS) networks of different molecular weights between junctions are interpreted in terms of the constrained junction model of rubber elasticity. The theory shows quantitative agreement with experimental data, without the necessity of adjusting any parameter. Based on this agreement, one may conclude that in PDMS networks, the dependence of orientation on deformation results from the non-affine transformation of junction points, and that local intermolecular contributions to segmental orientation are not significant. In the case of less flexible chains such as polyisoprene on the other hand, intermolecular contributions to segmental orientation might be relatively more important. Correspondence between birefringence experiments and segmental orientation is formulated which permits direct quantitative comparison between the birefringence and FTi.r. dichroism experiments.