From Simple Liquid to Polymer Melt. Glassy and Polymer Dynamics Studied by Fast Field Cycling NMR Relaxometry: Low and High Molecular Weight Limit

Abstract

Fast field cycling (FFC) NMR is applied to study the dispersion of the 1H spin−lattice relaxation in the low molecular weight glass-formers o-terphenyl, tristyrene, and oligomeric polybutadiene (PB, with M/gmol−1 = 355 and 466) over a broad temperature range (203−401 K). Differing from previous FFC NMR works, we analyze the relaxation data in the susceptibility form ω/T 1(ω), and applying frequency−temperature superposition, master spectra are obtained covering up to 8 decades in frequency. In all cases solely the glassy dynamics (α-process) determines the relaxation behavior, and the Rouse unit is estimated to M R ≅ 500 g/mol. The time constant τα(T) in the range 10−11−10−6 s is extracted, which agrees well with those measured at the same time by dielectric spectroscopy. For the high molecular weight PB (M/gmol−1 = 56 500, 87 000, 314 000, and 817 000) pronounced polymer effects are observed at low frequencies (ωτα ≪ 1) which are isolated from the total spectrum by subtracting the “glass spectrum” as obtained from low molecular PB. We argue that unless the underlying α-relaxation is properly accounted for, the apparent power law spectrum does not reflect the actual polymer dynamics.

Time Domain NMR in Polymer Science: From the Laboratory to the Industry

“…However, higher mobility than predicted in the regime II was found, indicating a less static tube constraint [61]. Regime 0 and I are instead usually investigated with fast-field cycling experiment [62][63][64].…”

Application of proton field‐cyclingNMRrelaxometry for studying translational diffusion in simple liquids and polymer melts

“…Sometimes, it is of interest to display the relaxation dispersion also in the generalized susceptibility representation based on the connection of linear response theory and the fluctuation‐dissipation theorem . Equilibrium fluctuations described by J ( ω ) are connected to the response represented by a (normalized) dynamic susceptibility according to .…”

Proton spin dynamics in polymer melts: New perspectives for experimental investigations of polymer dynamics

“…As a continuation of the pioneering work of Kimmich and collaborators [7] the dynamics of linear polymers such as 1,4-polybutadiene (PB) with different M has been studied by field-cycling (FC) 1 H NMR relaxometry [13,15,19,24,[55][56]. Transforming the measured relaxation rates Applying FTS the correlation loss is probed over nine decades in time and eight in amplitude.…”

“…The dynamics of the investigated systems is mainly reflected through characteristic features of nuclear spin relaxations. Important findings of recent years [7,[11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30], affecting the understanding of the proton spin dynamics in polymer melts are the subject of discussion of this paper.…”