Novel phase separated multi-phase materials combining high viscoelastic loss and high stiffness

In a previous study we showed that a unique combination of high stiffness and high viscoelastic loss could be achieved by filling a polystyrene matrix with rigid inorganic spheres coated with a thin (∼200 nm) layer of a viscoelastic material. The sandwiching of this ‘lossy’ layer between the two rigid components was found to give a significant amplification of the tanδ loss peak associated with this material, without significantly compromising the sample stiffness. This was an experimental validation of the effect originally proposed by Gusev using finite element numerical studies. Following on from this, in the current study we have developed this concept further and shown that a similar amplification of viscoelastic loss can be achieved by incorporating rigid, but uncoated, particles into a phase separated matrix blend of polystyrene (PS) and a polystyrene/polyisoprene/polystyrene triblock co-polymer (SIS). The inspiration for this choice of the PS/SIS blend as the matrix came from some previous work where we studied, and modelled, the viscoelastic properties of these materials. In this work we show that in the filled PS/SIS blends, the loss amplification effect can been seen for different PS/SIS ratios, for different SIS polymers with different glass transition temperatures and also for glass fibres as well as for spherical particles. The key to seeing this effect is the fact that the SIS rubber phase was found to form a thin coating on the surface of the embedded particles during processing, effectively producing a surface coating layer on the particles (as well as phase separating within the PS matrix). As with our previous studies, it is shown that the experimentally measured effects are closely predicted by numerical micromechanical modelling based on the measured bulk properties of the three discrete components.