  We investigate the origin of yield stress aging in semi-dense, saline, and
turbid suspensions in which structural evolution is rapidly arrested by the
formation of thermally irreversible roll-resisting interparticle contacts. By
performing optical tweezer (OT) three-point bending tests on particle rods, we
show that these contacts yield by overcoming a rolling threshold, the critical
bending moment of which grows logarithmically with time. We demonstrate that
this time-dependent contact-scale rolling threshold controls the suspension
yield stress and its aging kinetics. We identify a simple constitutive relation
between the contact-scale flexural rigidity and rolling threshold, which
transfers to macroscopic scales. This leads us to establishing a constitutive
relation between macroscopic shear modulus and yield stress that is generic for
an array of colloidal systems.
