Abstract
The rheological properties of soft materials often exhibit surprisingly universal linear and nonlinear features. Here we show that these properties can be unified by considering the effect of the strain-rate amplitude on the structural relaxation of the material. We present a new form of oscillatory rheology, strain-rate frequency superposition (SRFS), where the strain-rate amplitude is fixed as the frequency is varied. We show that SRFS can isolate the response due to structural relaxation, even when it occurs at frequencies too low to be accessible with standard techniques.
Highlights
We present a new form of oscillatory rheology, strain-rate frequency superposition (SRFS), where the strain-rate amplitude is fixed as the frequency is varied
We show that SRFS can isolate the response due to structural relaxation, even when it occurs at frequencies too low to be accessible with standard techniques
While this picture provides an excellent description of a colloidal supercooled liquid, the underlying physical concept should be much more generally applicable. If this link is verified, the relaxation could be probed using the nonlinear response, even when the relaxation frequency is experimentally inaccessible. This would provide a new probe of the dynamics and rheology of soft materials
Summary
The similarities in the rheological response of these materials extend even to nonlinear measurements, characterized by strain-dependent viscoelastic measurements performed at constant !, varying the strain amplitude. The peak in G00 0 observed in nonlinear measurements is directly related to a decrease of the structural relaxation time with increasing shear rate [7,10 –13]; the applied strain drives the relaxation and forces it to a higher frequency, where it is directly probed. This new technique, which we call strain-rate frequency superposition (SRFS), should be generally applicable to the study of many soft materials.
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