Glassy and Polymer Dynamics of Elastomers by ¹H-Field-Cycling NMR Relaxometry: Effects of Fillers

¹H spin-lattice relaxation rate (R₁) dispersions were acquired by field-cycling (FC) NMR relaxometry between 0.01 and 35 MHz over a wide temperature range on polyisoprene rubber (IR), either unfilled or filled with different amounts of carbon black, silica, or a combination of both, and sulfur cured. By exploiting the frequency-temperature superposition principle and constructing master curves for the total FC NMR susceptibility, χ″(ω) = ωR₁(ω), the correlation times for glassy dynamics, τ_s, were determined. Moreover, the contribution of polymer dynamics, χ_pol^″(ω), to χ″(ω) was singled out by subtracting the contribution of glassy dynamics, χ_glass^″(ω), well represented by the Cole-Davidson spectral density. Glassy dynamics resulted moderately modified by the presence of fillers, τ_s values determined for the filled rubbers being slightly different from those of the unfilled one. Polymer dynamics was affected by the presence of fillers in the Rouse regime. A change in the frequency dependence of χ_pol^″(ω) at low frequencies was observed for all filled rubbers, more pronounced for those reinforced with silica, which suggests that the presence of the filler particles can affect chain conformations, resulting in a different Rouse mode distribution, and/or interchain interactions modulated by translational motions.