Rheological properties of poly(dimethylsiloxane)-poly(diethylsiloxane) blends

The rheological behavior of poly(dimethylsiloxane)-poly(diethylsiloxane) blends in the range 20 to 100°C, including the region of existence of poly(diethylsiloxane) in mesomorphic and amorphous states has been studied by capillary viscometry. The flow of these blends within the studied shear stress interval between 10³ and 10⁵ Pa obeys a power law. If poly(diethylsiloxane) is introduced in the mesomorphic state and serves as a matrix, the blends behave as viscoplastic bodies and feature the yield stress. The flow of these blends is accompanied by an appreciable orientation of the poly(diethylsiloxane) phase. Blends in which the mesomorphic poly(diethylsiloxane) is a disperse phase flow as abnormally viscous fluids in which poly(diethylsiloxane) plays the role of a structuring filler. The isotropization of poly(diethylsiloxane) leads to a reduction in its viscosity and, accordingly, in the viscosity of the blend. The logarithm of the effective viscosity of such blends both at the constant shear rate and constant shear stress is the linear function of their composition. The addition of poly(diethylsiloxane) to poly(dimethylsiloxane) strongly affects the degree of swelling of an extrudate at the exit of a capillary, and this parameter depends on the phase state of poly(diethylsiloxane) and its content in the blend. Upon incorporation of a small amount of a poly(dimethysiloxanel)-poly(diethylsiloxane) block copolymer (compatibilizer) into the blend, the viscosity of the blend approaches that of the predominant component. This phenomenon is apparently related to the fact that the block copolymer facilitates development of a more uniform morphology of the blend, in particular, the continuous dispersion phase. This factor, along with the specifics of the deformational behavior of poly(diethylsiloxane), also manifests itself during drawing and subsequent shrinkage of crosslinked resins prepared from the blends under study.