Length-Scale Dependence of Block Copolymer Segmental Dynamics*

This work examines the effect of interface proximity and tethering on polymer segmental motion. Selectively deuterated block copolymers (BCPs) were studied with neutron spin echo (NSE) spectroscopy. A strongly segregated BCP was used as a model system in which a glassy deuterated polystyrene (dPS) block acted as the interface and the dynamics of a rubbery deuterated polyethylene oxide (dPEO) block was studied. The PEO block was selectively protonated as a label to examine the dynamics near the interface in one sample and near the chain end in another sample. A strong slowing of segmental dynamics in the sample with the protonated label tethered directly to the dPS was observed compared to the dynamics of the sample with the protonated label at the chain end, but with an unexpected length scale dependence. The slowing was only observed at length scales significantly larger than the characteristic PEO segment length (1 nm), and the disparity between interfacial and chain-end dynamics grew with increasing length. The novelty of examining polymer chain motion over a wide range of length scales is enabled by NSE of selectively deuterated BCPs and can impact BCP applications including batteries, water treatment, and gas separations.