Shear Rheology of An 2D Colloidal Monolayer

We describe experimental and theoretical investigations into the shear response of a 2D monolayer of charged, micron-scale particles at a decane/water interface. Even at low area fractions, electrostatic repulsions drive the colloids to form a crystalline monolayer. We place a ferromagnetic microbutton probe within the colloidal monolayer, upon which we exert a defined torque with external electromagnets. Direct visualization of the monolayer while shearing allows us to correlate local dynamics with applied stress. We report elastic modulus and yield stress as functions of particle concentration and pressure, and describe the dynamics as the monolayer yields.