Linear viscoelasticity of physically aging soft glassy (Thixotropic) materials

Abstract

Soft glassy materials are distinguished by their arrested microstructures and out-of-equilibrium thermodynamic states. These materials exhibit time dependent evolution of viscoelastic properties, driven by structural buildup under quiescent conditions, known as physical aging. As a result, they do not obey the standard linear viscoelastic framework, which is well-established for equilibrium materials. This article explores the application of linear viscoelastic principles to soft glassy materials by employing the effective time theory that readjusts the material clock to address the time dependence associated with the same. We explore how the effective time domain approach validates key linear viscoelastic principles, including the Boltzmann superposition principle, convolution relation, time–temperature superposition, time–stress superposition, and the Fourier transform relationship between relaxation modulus and complex modulus. We also discuss the relationship between soft glassy materials and thixotropy. These insights highlight the critical role of effective time in comprehending the intricate rheological characteristics of soft glassy materials.