  A model is proposed that considers aging and rejuvenation in a soft glassy
material as respectively a decrease and an increase in free energy. The aging
term is weighted by inverse of characteristic relaxation time suggesting
greater mobility of the constituents induce faster aging in a material. A
dependence of relaxation time on free energy is proposed, which under quiescent
conditions, leads to power law dependence of relaxation time on waiting time as
observed experimentally. The model considers two cases namely, a constant
modulus when aging is entropy controlled and a time dependent modulus. In the
former and the latter cases the model has respectively two and three
experimentally measurable parameters that are physically meaningful. Overall
the model predicts how material undergoes aging and approaches rejuvenated
state under application of deformation field. Particularly model proposes
distinction between various kinds of rheological effects for different
combinations of parameters. Interestingly, when relaxation time evolves
stronger than linear, the model predicts various features observed in soft
glassy materials such as thixotropic and constant yield stress, thixotropic
shear banding, and presence of residual stress and strain.
