Recent NMR investigations on molecular dynamics of polymer melts in bulk and in confinement

• New hardware and frequency-time superposition increase frequency range of NMR relaxation.
• Isotopic dilution allows distinction of inter- and intermolecular dipolar contributions.
• Experiments and theory demonstrate the dominance of intermolecular effects at low fields.
• Separation of these effects allows quantification of local diffusion parameters.

Polymer dynamics in the melt state cover a wide range in time and frequency, for both molecular weights below and above the entanglement length. Nuclear Magnetic Resonance (NMR) offers a number of techniques that cover a broad section of this frequency range, with frequency dependent (i.e., magnetic field dependent) relaxometry providing the widest window. Combining fast field cycling techniques with frequency–temperature superposition has recently improved the understanding of polymer melt dynamics from the local to global range. At the same time, a detailed theoretical approach that separates intra- and intermolecular contributions to relaxation times has been developed. These methods are shown to improve the description of segmental dynamics in polymers, being related to time-dependent diffusion coefficients, and to distinguish between these two different relaxation contributions for a number of model compounds. The findings represent the foundation for a more thorough understanding of polymers under external restrictions and bear potential to provide a conceptually new access to biopolymer dynamics and interactions.

Figure optionsDownload high-quality image (192 K)Download as PowerPoint slide