H. W. Meyer, H. Schneider, K. Saalwächter.
Proton NMR spin diffusion studies of PS-PB block copolymers at low-field: two- vs. three-phase model and recalibration of spin-diffusion coeffcients.
Polym. J. , accepted (2012).
Low-field proton nuclear magnetic resonance (NMR) methods were used to assess the phase fractions, domain thicknesses, T1 relaxation properties and spin-diffusion coefficients D of different phases in nanophase-separated polystyrene-polybutadiene (PS-PB) block copolymers. At low field, spin diffusion experiments are challenged by rather short longitudinal relaxation times (T1), requiring careful consideration of the interplay of T1 relaxation and spin diffusion effects. Building on earlier work (Mauri et al., Solid State Nucl. Magn. Reson. 34 (2008) 125), we a used numerical fitting procedure for a separate as well as combined analysis of phase-resolved rigid- and mobile-phase filtered spin diffusion as well as saturation recovery curves taken on a well-defined lamellar sample. We demonstrate the advantages in using three-component model, distinguishing a rigid and a mobile as well as an interphase that can be resolved by fits to the refocussed free-induction decay. We further use domain sizes from small-angle x-ray scattering as a gauge and find that spin diffusion coefficients from literature calibrations are overestimated. Under static low-field conditions, Δ for the rigid PS phase is found to be 0.38±0.06 nm2/ms, and we propose a re-scaling of a literature calibration correlating D for the mobile phase with its T2 relaxation time.