Dynamical heterogeneity in aging colloidal glasses of Laponite

Abstract

Glasses behave as solids due to their long relaxation time; however the origin of this slow response remains a puzzle. Growing dynamic length scales due to cooperative motion of particles are believed to be central to the understanding of both the slow dynamics and the emergence of rigidity. Here, we provide experimental evidence of a growing dynamical heterogeneity length scale that increases with increasing waiting time in an aging colloidal glass of Laponite. The signature of heterogeneity in the dynamics follows from dynamic light scattering measurements in which we study both the rotational and translational diffusion of the disk-shaped particles of Laponite in suspension. These measurements are accompanied by simultaneous microrheology and macroscopic rheology experiments. We find that rotational diffusion of particles slows down at a faster rate than their translational motion. Such decoupling of translational and orientational degrees of freedom finds its origin in the dynamic heterogeneity since rotation and translation probe different length scales in the sample. The macroscopic rheology experiments show that the low frequency shear viscosity increases at a much faster rate than both rotational and translational diffusive relaxation times.

12 pages, 5 figures, Accepted in Soft Matter 2012

References in corpus (9)

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Cited by in corpus (8)

• Microstructure and Soft Glassy Dynamics of Aqueous Laponite Dispersion
• Validity of Stokes-Einstein Relation in Soft Colloids up to the Glass Transition
• Direct Measurement of the Free Energy of Aging Hard-Sphere Colloidal Glasses
• Use of ultrasound attenuation spectroscopy to determine the size distribution of clay tactoids in aqueous suspensions
• Time reversibility during the ageing of materials
• Sedimentation stability and aging of aqueous dispersions of Laponite in the presence of cetyltrimethylammonium bromide
• Correlating microscopic viscoelasticity and structure of an aging colloidal gel using active microrheology and cryogenic scanning electron microscopy
• Real-space observation of salt-dependent aging in Laponite gels