Study on strain stiffening of non-colloidal suspension in oscillating shear by a subsequent steady shear test

Abstract

Rheological behavior of non-colloidal suspensions in oscillatory shear has been studied experimentally. With increase of strain amplitude, both storage and loss moduli first decrease and then increase at a critical point, which is called strain stiffening. Our experiment results show that suspension with small particles exhibit a larger modulus before the critical strain amplitude, and additional steady shear tests also show similar phenomenon. According to particle size distribution measurement, there is certain amount of small size particles which may have significant Brownian motion, and play a crucial role in shear thinning. Special experiment procedure is designed to investigate strain stiffening, two different tests of oscillating shear are parallel conducted and they are stopped at the strain amplitude corresponding to the critical point and peak point respectively. Both of them are further tested by a subsequent steady shear test (with constant shear rate) to inspect the internal particle structures. Samples with oscillating tests stopped at the critical point and peak point show similar magnitudes of shear viscosity in the steady shear tests. It is conjectured that particles in non-colloidal suspension exist as a metastable structure during strain stiffening, which can maintain a relatively stable configuration in oscillatory shear, but the structure will be broken rapidly in steady shear with the increase of shear rate. As a result of this, the metastable structure only affects the modulus in oscillatory shear, but does not affect the viscosity of steady shear.