Dependence of Order and Dynamics in Polymers and Elastomers under Deformation Revealed by NMR Techniques

Abstract

Uniaxial stretching and swelling are considered as two limiting cases of deformations of elastomers. Under both conditions, the molecular dynamics is changed with respect to the behavior that describes the undisturbed, equilibrium elastomer. Particularly the spectrum of segmental motions, which reveals itself in the frequency-dependence of the longitudinal NMR relaxation time, is discussed in this study, but also order effects expressed via the dipolar coupling strength are investigated. For stretched elastomers, a significant change of the relaxation dispersion is found for three different types of rubber; it is a consequence of a change of the mode spectrum of segmental motions that becomes obvious at low frequencies (below 1 MHz at room temperature). In swollen elastomers, on the other hand, a cross-over towards a behavior expected for semi-dilute solutions is found, and a comparison to solutions of uncross-linked polymers reveals a significant effect of the cross-links only in the kHz range. A much more pronounced difference between elastomers and polymer solutions, however, is found from double--quantum encoded NMR measurements where the residual order introduced by the presence of permanent cross-links is maintained even in the presence of solvent.

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

“…FC NMR relaxometry results on PB, PI, and PDMS have also been reported by the Kimmich and the Stapf group , and very similar experimental results have been obtained as in the present study. However, varying systematically molecular mass including the low- M limit, and most important constructing master curves allows us to achieve futher-reaching conclusions . − …”

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

“…In particular, as shown in the inset of Figure 5 , at low reduced frequencies (ωτ s ≤ 0.001), γ ranges between 0.22 and 0.26 for IR_S2_CB80, IR_S2_Si50, and IR_S2_Si15_CB20 while it goes down from 0.24 to 0.18 on decreasing the frequency for IR_S2. These changes of γ, resulting from the addition of fillers to rubber, are analogous to those observed for stretched rubbers, 69 − 71 , 88 polymer films on surfaces, 89 , 90 or for a soft polymer confined between lamellae of a rigid polymer in diblock and triblock copolymers. 71 , 91 In all cases, geometrical confinement is imposed on chain motions either by external forces or by interactions with solid surfaces.…”

“…In particular, as shown in the inset of Figure , at low reduced frequencies (ωτ s ≤ 0.001), γ ranges between 0.22 and 0.26 for IR_S2_CB80, IR_S2_Si50, and IR_S2_Si15_CB20 while it goes down from 0.24 to 0.18 on decreasing the frequency for IR_S2. These changes of γ, resulting from the addition of fillers to rubber, are analogous to those observed for stretched rubbers, − , polymer films on surfaces, , or for a soft polymer confined between lamellae of a rigid polymer in diblock and triblock copolymers. , In all cases, geometrical confinement is imposed on chain motions either by external forces or by interactions with solid surfaces. Therefore, the different values of γ could be associated with changes in chain conformations induced by interactions with surfaces, , resulting in partial chain alignment close to the surface, and in different mode distributions at lengths on the order of the length scale of Rouse motions.…”

Contrast variation by dynamic nuclear polarization and time-of-flight small-angle neutron scattering. I. Application to industrial multi-component nanocomposites

“…The static structure, which is a target of this contrast variation SANS study, was not affected by the addition of TEMPO. On the other hand, regarding dynamic properties, the storage and loss modulus (Busfield et al, 2000) and the longitudinal and transverse proton relaxation times (Stapf & Kariyo, 2005) were affected by the addition of small organic molecules (a few per cent in weight), which is known as the 'plasticizer' effect. Fig.…”