Quasi-elastic neutron scattering study on dynamics of polymer gels with controlled inhomogeneity under uniaxial...

We study the segmental and monomer dynamics of polymer gels with controlled inhomogeneity under uniaxial deformation by means of quasi-elastic neutron scattering (QENS). In order to clarify the effect of the homogeneity of a network structure on the polymer dynamics in gels, we compare two types of polymer gels with controlled homogeneity: a homogeneous tetra-PEG gel (homo-gel) prepared from uniform tetra-arm pre-polymers and a heterogeneous tetra-PEG gel (hetero-gel) with a small amount of shorter tetra-PEG pre-polymer. The different inhomogeneity in the homo-gel and the hetero-gel has little effect on the average relaxation time of the chain dynamics in the undeformed state. The difference in the local dynamics in the gels is emphasized under uniaxial deformation: while the homo-gel shows a single relaxation mode, the hetero-gel exhibits a bimodal distribution of relaxation times with a slow dynamic mode ascribed to highly stretched short strands, which causes a more brittle macroscopic fracture compared with that in the case of the homo-gel.