RESUMO
The flow behavior of soft materials below the yield stress can be rich and is not fully understood. Here, we report shear-stress-induced reorganization of three-dimensional solid-like soft materials formed by closely packed nematic domains of surfactant micelles and a repulsive Wigner glass formed by anisotropic clay nano-discs having ionic interactions. The creep response of both the systems below the yield stress results in angular velocity fluctuations of the shearing plate showing large temporal burst-like events that resemble seismic foreshocks-aftershocks data measuring the ground motion during earthquake avalanches. We find that the statistical properties of the quake events inside such a burst map on to the scaling relations for magnitude and frequency distribution of earthquakes, given by Gutenberg-Richter and Omori laws, and follow a power-law distribution of the inter-occurrence waiting time. In situ polarized optical microscopy reveals that during these events the system self-organizes to a much stronger solid-like state.
RESUMO
We investigate the response of the two-dimensional (2D) continuous non-particulate film of surfactant sorbitan tristearate confined at the air-water interface under oscillatory shear deformation. The time dependence of various rheological parameters show critical-like behavior at a value of strain amplitude close to the crossover point of elastic ([Formula: see text]) and viscous ([Formula: see text]) shear moduli. Imposing oscillatory shear of different strain amplitudes ([Formula: see text]) above and below the crossover strain amplitude ([Formula: see text]) over a large number of cycles, we quantify the temporal dependence of interfacial viscous modulus, phase angle ([Formula: see text]) as well as higher harmonic components of stress. The number of shear cycles ([Formula: see text]) required for these quantities to reach the steady state value diverges near [Formula: see text]. The steady state values of the third harmonic ([Formula: see text]) show order parameter like behavior indicating the importance of higher order harmonics near the nonequilibrium transition. We further show that the energy dissipation per cycle per unit volume has a marked change near [Formula: see text], consistent with continuum level nonequilibrium shear-transformation-zone model of amorphous viscoplasticity.