Glassy, Rouse, and Entanglement Dynamics As Revealed by Field Cycling1H NMR Relaxometry

Abstract

Poly(propylene glycol), poly(isoprene), and poly(dimethlyl siloxane) (PDMS) of different molecular masses M are investigated by field-cycling 1H NMR relaxometry to monitor the crossover from segmental dynamics, to Rouse and entanglement dynamics. The spin–lattice relaxation dispersions T1(ω) obtained at different temperatures (160 K – 400 K) are converted to the susceptibility representation χ″DD (ω) = ω/T1(ω). Applying frequency–temperature superposition, the data are merged to provide master curves χ″DD (ωτs) with τs = τs(T) being the segmental correlation times. Combining them with those from dielectric spectroscopy about 12 decades in time are covered. A similar M dependence of χ″DD (ωτs) is observed for all polymers (t ≫ τs) and comparison with dielectric normal mode spectra is carried out. In the case of PDMS showing particularities at t ≈ τs we attempt to separate intra- and intermolecular relaxation contributions. Transformation into time domain yields the dipolar correlation function CDD(t/τs) wh...