Experimental determination of rheological properties of polydimethylsiloxane

Abstract

A series of linear polydimethylsiloxane of different molecular weight and with reduced polydispersity were prepared by partial fractionation of commercial products. The rheological functions, i.e. zero shear viscosity ( η 0), first and second normal stress coefficients ( Ψ 10 and Ψ 20), of the materials were experimentally measured by conventional rotational rheometers and by a rotation rod apparatus. The relationships between molecular structure (molecular weight and polydispersity index) and rheological functions are presented and discussed on the basis of equations proposed in the literature. Zero shear viscosity data conform to the well-known dependence on a power 3.5 of molecular weight. However, a consistently stronger influence of molecular weight over Ψ 10 and Ψ 20 is found. The influence of polydispersity over Ψ 10 is also analyzed.