Shear-Induced Reversibility of quasi-2D Colloids in Presence of Thermal Noise

The effects of thermal noise on particle rearrangements in colloidal suspensions undergoing cyclic shear are experimentally investigated using particle tracking methods. The experimental model system consists of polystyrene particles adsorbed at an oil- water interface, in which the particles exhibit small but non-negligible Brownian motion. We perform experiments on bidisperse (1 and 1.2 $\mu$m in size) colloidal samples with area fractions ($\phi$ ) of 0.20 and 0.32. Reversibility of particle rearrangements are characterized, and we show that unlike dense athermal systems, reversible clusters are not stable; once a particle enters into a reversible trajectory, it has a nonzero probability of becoming irreversible in the following shearing cycle. This probability was previously found to be approximately zero for an analogous athermal system. We demonstrate that the stability of reversibility depends both on packing fraction, $\phi$ , and the shearing amplitude, $\gamma_0$. In addition, we identify hysteresis in the dynamics of rearrangements for reversible particles, which indicates that such rearrangements are dissipative. At lower packing fractions, this hysteresis becomes less prominent, and the dynamics is moved closer to equilibrium by thermal noise.