Physicochemical Effects in Aging Aqueous Laponite Suspensions

Abstract

We study aging behavior of an aqueous suspension of Laponite as a function of concentration of Laponite, concentration of salt, time elapsed since preparation of suspension (idle time), and temperature by carrying extensive rheological and conductivity experiments. We observe that temporal evolution of elastic moduli, which describes structural build-up and aging, shifts to low times for experiments carried out for higher concentration of Laponite, higher concentration of salt, greater temperature, and longer idle time while preserving the curvature of evolution in the solid regime (elastic modulus greater than viscous modulus). Consequently appropriate shifting of evolution of elastic modulus in the solid regime leads to aging time-idle time-salt concentration-Laponite concentration-temperature superposition. The existence of such a superposition suggests the generic nature of microstructure buildup irrespective of mentioned variables in the explored range. The behavior of shift factors needed to obtain the superposition indicate that the energy barrier associated with structural buildup decreases with an increase in idle time and temperature and decreases linearly with an increase in concentration of Laponite and that of salt. The conductivity experiments show that ionic conductivity of the suspension increases with increasing Laponite concentration, salt concentration, temperature, and very importantly the idle time. We also analyze the interparticle interactions using DLVO theory that suggests an increase in idle time, temperature, and salt concentration increases the height of the repulsive energy barrier while it decreases the width of the same when particles approach each other in a parallel fashion. However when particles approach each other in a perpendicular fashion, owing to dissimilar charges on edge and face, the energy barrier for the attractive interaction is expected to decrease with an increase in idle time, temperature, and salt concentration. Analysis of rheological and conductivity experiments suggests a strong influence of attractive interactions on the low energy structures in an aqueous suspension of Laponite.

Kinetics of the glass transition of fragile soft colloidal suspensions

“…< τ ww > is plotted for different values of T with C L =3.0% w/v and C S =0.05 mM in figure 2(e). It is seen that increase in T accelerates the time-evolution of < τ ww > [26,32]. In figure 2(f), D (•) and t ∞ α ( ) are plotted for the data shown in figure 2(e).…”

Microstructure and Soft Glassy Dynamics of an Aqueous Laponite Dispersion

“…As a result, soft glassy dynamics of aqueous dispersion of Laponite has been investigated as a model system to understand wide class of industrial pasty systems as well as other model soft glassy materials. 10,43,47 Furthermore, owing to accessible timescales and length-scales in Laponite dispersion compared to that of in the molecular glassy systems, the former is analyzed to obtain insight into comparatively inaccessible dynamics of the latter. Dynamic Light Scattering (DLS) has been used very extensively to study soft glassy dynamics of an aqueous dispersion of Laponite.…”

“…Figure 12 shows a schematic representation of W as a function of d , wherein the height of the repulsive barrier (proportional to k ) can be seen to be increasing while its width (proportional to 1 k ) can be seen to be decreasing with increase in the concentration of cations in the dispersion. 10 The case discussed in figure 12 corresponds to a limiting case of two particles approaching each other in a parallel fashion. However parallel approach is just one of the possible scenarios, as in reality Laponite particles can approach each other in any orientation.…”

Exfoliation Dynamics of Laponite Clay in Aqueous Suspensions Studied by NMR Relaxometry

“…A lot of research has been dedicated to such processes in Laponite suspensions as gelation [1][2][3] , dispersing 4,5 , sedimentation 2 , dissolution of particles 6 . Alongside the fundamental interest, quantitative research of Laponite exfoliation process is important for a range of Laponite applications.…”