A new and universal relationship between two different viscosity functions
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초록
내용
Generally, at high shear rates, getting a steady-shear viscosity of soft materials is challenging due to edge fracture and shear instability. In this regard, the Cox-Merz rule provides access to the steady-shear viscosity that is useful for processing conditions without the instabilities associated with experiments. However, the Cox-Merz rule does not always hold true: It has been shown to work in some cases and fail in others. This rule remains phenomenological and rather obscure the interpretation of material responses. In this work, we revisit the Cox-Merz rule using recovery rheology, which decomposes the strain into recoverable and unrecoverable components. With recovery tests in mind, we elucidate why the Cox-Merz rule works only in a limited set of conditions and present an approach that could allow for universal comparisons to be made. We propose a new relationship that can replace the Cox-Merz rule, and demonstrate its universality using six materials.