¹H NMR spectroscopy of polymers under shear and extensional flow

Abstract

We discuss the potential insights gained from ¹H nuclear magnetic resonance (NMR) spectroscopy experiments on polymeric systems under both shear and extension, and we show in particular that ¹H spin-spin relaxation is sensitive to both molecular conformation and to molecular interactions. Rheo-NMR ¹H spectroscopy studies on semi-dilute solutions of polyacrylamide demonstrate that the chain protons exhibit a marked T ₂ reduction under shear and that the recovery on shear cessation is indicative of slow reorganisational dynamics. Studies of the wheat flour protein, gluten, indicate marked spectroscopic changes in the vicinity of the amidic resonances associated with glutamine residues, an effect we attribute to the disruption of hydrogen bonding.