Abstract
Novel methods of nitroxyl spin labelling suitable for molecular dynamics studies within the interface regions of SBR elastomer/silica composites have been developed and used together with the nitroxyl spin probe technique. Fast and slow motional components have been identified within the interface regions and the corresponding rotational diffusion tensors have been measured as a function of the temperature and the SiO2 concentration. The fast rotational frequency is found to be orders of magnitude slower than that measured in the absence of SiO2. This difference is suggested to arise from a closer packing of the macromolecules near the silica surface caused by the van der Waals bonding interactions. Increase of the SiO2 concentration results in a decrease of the molecular mobility. This effect has been imputed to the overlapping of the bonding interaction regions. Spin probe measurements in the SBR-SiO2 matrices using TEMPO, strongly suggest that the hindrance to chain segmental motion induced by the SiO2-SBR interactions propagates beyond the interface regions thus involving the bulk polymer matrix. It is suggested that the information on the segmental chain dynamics obtained through the spin labelling and spin probe measurements can be developed as a method for investigating the polymer/filler interactions within the reinforcing mechanism by the filler.
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