Interpenetration of chemically identical polymer onto grafted substrates

Interpenetrating interfaces between a deuterated polystyrene (dPS) and the grafted substrates with the same chemical identity were characterized using neutron reflectivity (NR) measurements, where the PS-grafted substrates were prepared using a grafting-to approach with hydroxyl end-functionalized polystyrene (PSOH) in a dry brush regime. The characteristic brush thickness (h) and grafting density (σ) of PS-grafted layers were determined based on the chain length (or molecular weight, M_n) of PSOHs. The experimental interpenetration length (ξ) was measured at the interfaces, and the limiting plateau in ξ above which the value was independent of film thickness shifted toward higher values as the M_n of PSOH increased. Normalization by the deformed brush thickness (h_d) of PS-grafted layer after interpenetration revealed that the experimental value of ξ/h_d in a short and dense PS-grafted substrate, prepared with a low-molecular-weight PSOH, deviated markedly from the theoretical value, indicating significant additional stretching of the grafted chains to accommodate inter-mixing with the dPS chains.