Impact Propagation and Absorption Mechanisms in Two Dimensional Colloidal Monolayers

We report experimental and numerical studies on the propagation and absorption of localized mechanical pulses in two dimensional colloidal monolayers. The colloidal monolayers consist of hexagonal-packed and disordered arrays of SiO₂ microspheres (radius R = 3.69 um) immersed in solvent with different viscosities. We triggered the localized mechanical pulses by creating an isotropic pressure wave from pulsed laser ablation (532nm, 4ns) of a single gold-coated SiO₂ Janus microsphere and monitored the impact propagation at single particle level using a microscope system equipped with a high speed camera (300kHz frame rate). We modeled the dynamics of the systems considering hydrodynamic interactions, particle elasticity, and intermolecular forces and showed a good agreement with experimental observations. We will discuss the dependence of laser power, solvent viscosities, and spatial arrangement on the stress propagation.