Ultrasonic and microscopic investigation of blends of polydimethylsiloxaneand polyisobutylene at all concentrations

Polydimethylsiloxane/polyisobutylene blends are investigated using ultrason ic techniques (megahertz range), in the complete concentration range (0%-10 0%). The velocities of propagation and attenuations of shear and longitudin al waves are determined experimentally together with simultaneous optical m icroscopy observations. From the knowledge of the acoustical and physical p roperties of the separate polymers, the acoustical longitudinal parameters of the blend can be predicted successfully up to 40% volume concentration o f the dispersed phase, with a model developed by the authors and especially adapted to wave propagation in such viscoelastic emulsions. For shear wave s, two emulsion models (Palierne and Lee-Park) are used for predicting the viscoelastic moduli associated with the acoustical data at ultrasonic frequ encies, with a good agreement. The case of composite droplets (40%-60%) has required to consider Friedrich's extension of Palierne's model. The ultras onic method appears to be a very interesting tool for predicting phase inve rsion for polymer blends, as well as the evolution of the microstructure of the blend. Finally, this work provides an extension of the validity of emu lsion models in the high frequency range. (C) 2000 The Society of Rheology. [S0148-6055(00)01205-0].