2014/03/31 by Shweta Jatav, Yogesh M Joshi
Chemistry · Engineering · Materials Science · Physics and Astronomy · #Colloid #Electrostatics and Colloid Interactions #Material Dynamics and Properties #Phase Equilibria and Thermodynamics #Relaxation (psychology) #Rheology #Shear (geology) #Shear rate #Suspension (topology) #Viscoelasticity #Viscosity #Volume fraction #cond-mat.mes-hall #cond-mat.mtrl-sci #cond-mat.soft
paper · pdf · doi:10.1122/1.4887344
37 Pages, 7 figures, 1 table, To appear in Journal of Rheology
arxiv created 2014/07/06 · arxiv updated 2014/07/08 · openalex publication_date 2014/08/28 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/05
Colloidal suspensions that are out of thermodynamic equilibrium undergo physical aging wherein their structure evolves to lower the free energy. In aqueous suspension of Laponite, physical aging accompanies increases of elastic and viscous moduli as a function of time. In this work, we study temporal evolution of elastic and viscous moduli at different frequencies and observe that freshly prepared aqueous suspension of Laponite demonstrates identical rheological behavior reported for the crosslinking polymeric materials undergoing chemical gelation. Consequently at a certain time, tan δ is observed to be independent of frequency. However, for samples preserved under rest condition for longer duration before applying the shear melting, the liquid to solid transition subsequent to shear melting shows greater deviation from classical gelation. We also obtain continuous relaxation time spectra from the frequency dependence of viscous modulus. We observe that, with an increase in the rest time, continuous relaxation time spectrum shows gradual variation from negative slope, describing dominance of fast relaxation modes to positive slope representing dominance of slow relaxation modes. We propose that the deviation from gelation behavior for the shear melted suspensions originates from inability of shear melting to completely break the percolated structure thereby creating unbroken aggregates. The volume fraction of such unbroken aggregates increases with the rest time. For small rest times presence of fewer number of unbroken aggregates cause deviation from the classical gelation. On the other hand, at high rest times presence of greater fraction of unbroken aggregates subsequent to shear melting demonstrate dynamic arrest leading to inversion of relaxation time spectra.