Investigation of the dynamical slowing down process in soft glassy colloidal suspensions: comparisons with supercooled liquids

Abstract

The primary and secondary relaxation timescales of aging colloidal suspensions of Laponite are estimated from intensity autocorrelation functions obtained in dynamic light scattering (DLS) experiments. The dynamical slowing down of these relaxation processes are compared with observations in fragile supercooled liquids by establishing a one-to-one mapping between the waiting time since filtration of a Laponite suspension and the inverse of the temperature of a supercooled liquid that is rapidly quenched towards its glass transition temperature. New timescales associated with primary and secondary relaxation processes, such as the characteristic timescale associated with the slowdown of the secondary relaxation process and the glass transition time, are extracted to describe the phenomenon of dynamical arrest in Laponite suspensions. In results that are strongly reminiscent of those extracted from supercooled liquids approaching their glass transitions, it is demonstrated that a strong coupling exists between the primary and secondary relaxation processes of aging Laponite suspensions in the cage-forming regime. Furthermore, the experimental data presented here clearly demonstrate the self-similar nature of the aging dynamics of Laponite suspensions within a range of sample concentrations.

Kinetics of the glass transition of fragile soft colloidal suspensions

“…Details of the set-up are given elsewhere [17]. The normalized intensity autocorrelation function of the scattered light, g (2) (t) =…”

“…The evolution of microscopic relaxation timescales are studied for Laponite suspensions with different concentrations (C L ), added salt concentrations (C S ) and temperatures (T ) to observe the effects of these variables on the fragility parameter D. It is seen that the evolutions of relaxation timescales of Laponite for all C L , C S and T can be compared with molecular glass formers if the waiting time (t w ) of the former is mapped with the inverse of thermodynamic temperature (1/T ) of the latter [17]. The stretching exponent β, associated with non-Debye structural relaxation processes, is also extracted for different waiting times t w for samples of different C L , C S and T .…”

Characteristics of the secondary relaxation process in soft colloidal suspensions

“…Similarly, for the Laponite suspensions studied here, t g is defined as the waiting time at which < τ ww >= 100 sec and extrapolated from fits to equation 3. In figure 3(b), the characteristic timescale t [12]. Hence, the coupling between t ∞ β and t g (t ∞ β ∝ t g ) is reminiscent of the linear relationship between E β and T g in supercooled liquids [18,19].…”

“…It was demonstrated in an earlier work that Arrhenius and Vogel-Fulcher-Tammann (VFT) dependences of the fast and the slow relaxation times on waiting time respectively are obtained if the waiting time t w of a spontaneously evolving Laponite suspension is mapped with the inverse of the thermodynamic temperature 1/T of molecular glasses [12]. Consequently, the t w -dependence of τ 1 and < τ ww > are given by the following equations [12]:…”

“…It is seen from this figure that the C(t) data show two-step relaxations and that the slow relaxation processes progressively slow down with t w . The two-step relaxation process in C(t) can be expressed as the sum of an exponential and a stretched exponential decay [10][11][12].…”