Proton NMR spin-diffusion studies of PS-PB block copolymers at low field: Two- vs three-phase model and recalibration of spin-diffusion coefficients

Abstract

Low-field proton nuclear magnetic resonance (NMR) methods were used to assess the phase fractions, domain thicknesses, T 1 relaxation properties and spin diffusion (SD) coefficients D of different phases in nanophase-separated polystyrene-polybutadiene block copolymers. At low field, SD experiments are challenged by rather short longitudinal relaxation times (T 1), requiring careful consideration of the interplay of T 1 relaxation and SD effects. Building on earlier work, we used a numerical fitting procedure for a separate as well as combined analysis of phase-resolved rigid- and mobile-phase filtered SD, 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 refocused free-induction decay. We further use domain sizes from small-angle X-ray scattering as a gauge and find that SD coefficients from literature calibrations are overestimated. Under static low-field conditions, D for the rigid polystyrene phase is found to be 0.380.± 06 nm 2 ms -1, and we propose a rescaling of a literature calibration correlating D for the mobile phase with its T 2 relaxation time. © 2012 The Society of Polymer Science, Japan (SPSJ) All rights reserved.