The effect of fillers on the interfacial polymer properties from cryogenic dynamic mechanical measurements

Dynamic mechanical measurements were used to study the effect of high surface area carbon black and fused silica fillers and a number of simple organic diluents on the SBR (31.6 mol% styrene) peak, which is associated with small main chain motions of trans polybutadiene units. The amount of molecular motion eliminated from the glassy state by carbon black was greater than fused silica, indicating stronger polymer-filler interaction. The degree of interaction between polymer and filler at the interface affects polymer motion further removed from the filler surface. The reasons for this phenomenon are discussed. It is proposed that dilatational stresses resulting from the mismatch in the coefficients of expansion of filler and matrix are the cause of shifts in relaxation spectra to lower temperatures, which are more pronounced when polymer-filler interaction is weak. The toughness of the matrix near the interface is discussed in terms of polymer-filler interaction, the dilatational stresses and resulting shifts in the relaxation spectra. The effect of diluents on polymer motion in relation to diluent structure show no significant trends and is difficult to interpret without information on the percentage of diluent molecules existing in diluent clusters.