Magnetisation relaxation

Characterisation of Chemical and Physical Networks in Rubbery Materials Using Proton NMR Magnetisation Relaxation... 

The use of solid-state NMR magnetisation relaxation experiments to characterise network structures in various rubbery materials is reviewed in this chapter. Comprehensive reviews of high-resolution NMR techniques can be found elsewhere [21-23, 30-35]. 

Network Structure Analysis by Means of NMR Transverse Magnetisation Relaxation... 

Solid-state NMR magnetisation relaxation experiments provide a good method for the analysis of network structures. In the past two decades considerable progress has been made in the field of elastomer characterisation using transverse or spin-spin (T2) relaxation data [36-42]. The principle of the use of such relaxation experiments is based on the high sensitivity of the relaxation process to chain dynamics involving large spatial-scale chain motion in elastomers at temperatures well above the Tg and in swollen networks. Since chain motion is closely coupled to elastomer structure, chemical information can also be obtained in this way. 

Experimental studies of filled rubbers are complicated by several things, such as the effect of the magnetic susceptibility of the filler, the effect of free radicals present at the surface of carbon black, the complex shape of the decay of the transverse magnetisation relaxation of elastomeric materials due to the complex origin of the relaxation function itself [20, 36, 63-66], and the structural heterogeneity of rubbery materials. 

H NMR transverse magnetisation relaxation experiments have been used to characterise the interactions between NR, isoprene rubber, BR, EPDM and polyethylacrylate rubbers with hydrophilic silica and silicas modified with coupling agents [124-129]. These studies showed that the physical interactions and the structures of the physical networks in rubbers filled with carbon black and rubbers filled with silicas are very similar. In both cases the principal mechanism behind the formation of the bound rubber is physical adsorption of rubber molecules onto the filler surface. 

Low-Field NMR Magnetisation Relaxation Experiments for Quality Control Purposes... 

Of course, magnetisation relaxation rate information can be obtained from monitoring M as a function of time (t), for example following saturation of M (=Mo) and then switching the field off. This often follows an exponential law, such that the relaxation time (or, more correctly, time constant) t can be defined as ... 

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