Doctoral students seminar (November 5, 2019)

By using DQ-NMR technique, we could measure the end-to-end distance between the cross-links of the network. From the data, we can obtain information about the microscopic deformation of polymer chains under the deformation and swelling, thus verify the experimental results with different elasticity models. Previous investigations of our group on uniaxially stretched rubber shows on average a nonaffine behaviour, whereas isotropically swollen polymer networks were found to follow an affine expansion in the late stage of swelling .

In the current work, we are using DQ-NMR measurements in order to investigate microscopic stretching of polymer chains during anisotropic swelling and under different mechanical deformations (uniaxial and as well biaxial) of not only dry, but also swollen polymer networks.

The main focus is a comparison of chain deformation in dry and swollen state. The leading hypothesis for the present work is that the polymer chains of a highly swollen rubber may follow a more affine-like behaviour under deformation. In this study, we checked if chains are deformed at a higher extent in the swollen than in dry state. Our various combinations of swelling and stretching show that in swollen state under mechanical strain the network chains are stretched as weakly as in dry state. The reasons of such weak local deformation are most probably a high inhomogeneity and significant chain reorganization of the swollen network. Comparisons of the MQ-NMR data for mechanically deformed dry and then swollen rubber show that the averaged dipolar coupling is not changed, but its Distribution is considerably increased. This means that the swelling of the prestretched polymer network does not change the average relative configuration of chains but results instead in significant rearrangements.