Study of dynamical heterogeneities in colloidal nanoclay suspensions approaching dynamical arrest

Abstract

The dynamics of aqueous Laponite clay suspensions slow down with increasing sample waiting time (t w). This behavior, and the material fragility that results, closely resemble the dynamical slowdown in fragile supercooled liquids with decreasing temperature, and are typically ascribed to the increasing sizes of distinct dynamical heterogeneities in the sample. In this article, we characterize the dynamical heterogeneities in Laponite suspensions by invoking the three-point dynamic susceptibility formalism. The average time-dependent two-point intensity autocorrelation and its sensitivity to t w are probed in dynamic light scattering experiments. Distributions of relaxation time scales, deduced from the Kohlrausch-Williams-Watts equation, are seen to widen with increasing t w. The calculated three-point dynamic susceptibility of Laponite suspensions exhibits a peak, with the peak height increasing with evolving t w at fixed volume fraction or with increasing volume fraction at fixed t w, thereby signifying the slowdown of the sample dynamics. The number of dynamically correlated particles, calculated from the peak-height, is seen to initially increase rapidly with increasing t w, before eventually slowing down close to the non-ergodic transition point. This observation is in agreement with published reports on supercooled liquids and hard sphere colloidal suspensions and offers a unique insight into the colloidal glass transition of Laponite suspensions.

Microstructure and Soft Glassy Dynamics of an Aqueous Laponite Dispersion

“…This causes a broadening of the relaxation time distribution, and as a result, the relaxation dynamics becomes strongly nonexponential . Dynamic heterogeneity has also been observed in colloidal glassy systems ,− in general and in aqueous Laponite dispersions − in particular. One of the strong indications of dynamical heterogeneity is the nonexponential behavior of a relaxation process or the intermediate scattering function. ,, As discussed above, the stretched exponential relaxation dynamics with decreasing parameter β with aging time suggests a broadening of the relaxation time distribution, which can be attributed to the dynamical heterogeneities and their growth. ,, The size or length scales of the dynamical heterogeneities are extracted using higher-order correlation functions, which are the fluctuations of the two-point correlation function in space and time or with respect to the change in the control parameter.…”

“…68 It causes broadening of the relaxation time distribution, and as a result, the relaxation dynamics becomes strongly non-exponential. 69 The dynamic heterogeneity has also been observed in colloidal glassy systems 65,[67][68][69] in general and aqueous Laponite dispersion [70][71][72][73][74][75] in particular. One of the strong indications of dynamical heterogeneity is the non-exponential behavior of a relaxation process or the intermediate scattering function.…”

Anisotropic and heterogeneous dynamics in an aging colloidal gel

“…The dynamical processes occur over a wide range of length and time scales, slow down with the sample age and can be highly sensitive to the sample history. A large body of experiments using time resolved correlation techniques [1][2][3][4][5][6][7][8][9][10][11][12][13] , confocal microscopy [14][15][16][17] , differential dynamic microscopy 18 , and theory and simulations [19][20][21][22][23][24][25][26][27][28] have investigated the dynamics of colloidal gels [29][30][31] , providing deep insights into the structural origin of the relaxation mechanism such as caging, localization and cooperative particle rearrangements producing dynamical heterogeneities.…”

Electric field induced gelation in aqueous nanoclay suspensions

“…The changes between these phases can be brought about by the addition of salt or by increasing the colloidal volume fraction. Laponite is a synthetic smectite clay system which has been studied for its rheological merits and also as a fundamental model system to understand the colloidal glass transition [13,[15][16][17]. The structure of Laponite closely resembles the natural clay mineral hectorite with chemical formula Na and has a discotic shape with 25 nm diameter and 1 nm thickness.…”