EXPLORING THE DYNAMICS OF ELASTOMERS BY 1H FIELD CYCLING NMR RELAXOMETRY

Elastomers are polymeric materials extensively used for manufacturing a wide range of products for industrial applications. For this reason, great attention is focused on the production of new improved materials with well-defined mechanical properties. For this purpose, elastomers are usually characterized by mechanical measurements (modulus, strain at stress, etc.), which only provide macroscopic observables; however, in order to precisely guide the design of optimized materials with specific requirements, it is also crucial to obtain a description of the topology and dynamics of the polymer network at the molecular scale. Indeed, the mechanical properties of the material are strictly related to the mobility of the polymeric chains, which can be modulated for example by changing the amount of chemical cross-links or by adding reinforcing fillers (e.g. carbon black, nanosilica). In this field, 1H field-cycling (FC) NMR relaxometry represents an ideal technique to investigate complex polymer dynamics at the molecular level [1]. In fact, it allows the characterization of molecular motions over a broad time scale, by measuring 1H spin-lattice relaxation rates (R1 = 1/T1) on a wide range of Larmor frequencies (from 10 kHz to 35 MHz); this range can be further enlarged by combining experiments at different temperatures based on the frequency-temperature superposition (FTS) principle [2]. In this work, 1H FC NMR relaxometry was applied to characterize the effect of cross-linking [3] and the effect of filler [4] on polymer chain dynamics in a range of elastomeric materials of interest in the tire industry. The study allowed molecular dynamics to be carefully investigated over a quite broad time scale, ranging from local segmental motions to longer-range motions of the polymeric chains. References [1] R. Kimmich, N. Fatkullin Adv. Polym. Sci. 170, 1-113 (2004) [2] Y. Ding, A. P. Sokolov Macromolecules 39, 3322-3326 (2006) [3] F. Martini, E. Carignani, F. Nardelli, E. Rossi, S. Borsacchi, M. Cettolin, A. Susanna, M. Geppi, L. Calucci Macromolecules 53, 10028-10039 (2020) [4] F. Nardelli, F. Martini, E. Carignani, E. Rossi, S. Borsacchi, M. Cettolin, A. Susanna, M. Arimondi, L. Giannini, M. Geppi, L. Calucci J. Phys. Chem. B 125, 4546-4554 (2021)