Transient behavior of stress in a wormlike micellar solution under oscillatory shear

Abstract

Strain hardening and shear-induced structure (SIS) formation of a wormlike micellar solution under oscillatory shear is studied by separately controlling strain and shear rate amplitudes. Only when the oscillatory shear beyond the critical strain and shear rate amplitudes are applied is significant strain hardening behavior, which is attributed to the chain extension, observed. We find that the strength of the strain hardening, i.e., the chain extension, depends on the magnitude of the strain and shear rate amplitudes. As the oscillatory shear is repeatedly applied, the strength of the strain hardening is gradually reduced and approaches a periodic state. In the periodic state, stress response shows a triangular wave form but not an ideal sinusoidal response. Since these characteristic behaviors are observed above the critical conditions needed for the SIS formation, the periodic state will be attributed to the SIS formation. The level of the SIS in the periodic state can also be arbitrary controlled by a combination of these amplitudes. A close relation between the strain hardening and the SIS formation suggests that the degree of extension of the wormlike micellar chain affects the level of the SIS.