VISCOELASTIC MATERIAL FUNCTIONS OF NONCOLLOIDAL SUSPENSIONS WITH SPHERICAL-PARTICLES

We have characterized various steady and time-dependent material funct ions of suspensions of a non-Newtonian binder, poly(dimethyl siloxane) , incorporated with 10%-60% by volume of hollow and spherical glass be ads. The material functions included storage and the loss moduli, shea r stress and first normal stress difference growth and relaxation, rel axation modulus upon step strain and creep and recovery behavior. Both constant shear stress and shear rate experiments were carried out usi ng multiple rheometers over a broad temperature range (-35 to 40 degre es C) while following sample fracture and wall slip effects. With incr easing volume fraction, phi, of the noncolloidal particles, the strain range, over which linear viscoelastic behavior is observed, became na rrower and the relaxation time of the suspension increased. Increasing solid content gave rise to the development of the yield stress and th e dependence of large amplitude oscillatory shear properties on time a nd deformation history. The yield stress values increased with phi, bu t were not sensitive to temperature. For phi greater than or equal to 0.3 the first normal stress difference values reached reproducible and steady negative values (with tensile force positive). Larger negative values of the first normal stress difference were observed with incre asing deformation rate and solid concentration. The manifestations of the material functions resulting from the incorporation of the solids into the non-Newtonian binder included the suppression of the extrudat e swell and the dipping of the free surface in the Weissenberg experim ent. (C) 1997 The Society of Rheology.