Heterogeneity of polymers: Diluents nanoconfined in rubber networks and mechanical hole burning spectroscopy

Heterogeneity at micrometer or nanometer scale is of great importance and has drawn considerable attention in recent years. Many physical properties of materials, such as dynamic relaxation, diffusion or transport phenomenon can be affected and explained by the heterogeneous nature. The present dissertation focuses on the heterogeneity of polymers and consists of two parts of projects.

The first part of dissertation studies the nanoscale heterogeneity and structure in rubber networks. Thermoporosimetry is applied to characterize the network heterogeneity, which extends the Gibbs-Thomson model concerning the relationship between the melting point depression and the crystal size and requires the quantitative agreement between the Flory-Huggins theory and the melting points of the diluents in the uncrosslinked rubber. This dissertation presents the first systematic investigation on the validity of the Flory-Huggins theory in terms of melting point depression of diluents mixing with polymers. The correct use of thermoporosimetry to obtain the nanoheterogeneity of rubber networks and its calibration by controlled porous glasses are discussed and addressed.

The second part of dissertation focuses on the characterization of dynamic heterogeneity of polymers by means of a novel rheological method called Mechanical Spectral Hole Burning (MSHB). The MSHB on a triblock copolymer in the vicinity of its order-disorder transition is investigated. By successfully distinguishing the heterogeneity from homogeneity as well as different heterogeneity degrees, MSHB promises to be a potentially powerful tool to probe dynamic heterogeneity for polymeric materials. Additionally, the MSHB is further investigated on a series of polystyrene/ diethyl phthalate solutions. The effect of different types of heterogeneity such as entanglement length, entanglement density and chain end density is explored and different types of dynamics are examined by the MSHB. The results are consistent with a heterogeneous dynamics over the time scales from close to Rouse regime into the rubbery plateau regime and for the rubbery plateau-to-terminal flow transition regime. Terminal relaxation dynamics, on the other hand, is found to be homogeneous for the PS/diethyl phthalate solutions investigated.