Particle motion

AbstractThe movement of colloidal particles in simple and complex fluids and viscoelastic solids is central to the microrheology endeavor. All microrheology experiments measure the resistance of a probe particle forced to move within a material, whether that probe is forced externally or simply allowed to fluctuate thermally. This chapter lays a foundation of the fundamental mechanics of micrometer-dimension particles in fluids and soft solids. In an active microrheology experiment, a colloid of radius a is driven externally with a specifed force F (e.g.magnetic, optical, or gravitational), and moves with a velocity V that is measured. Of particular importance is the role of the Correspondence Principle, but other key concepts, including mobility and resistance, hydrodynamic interactions, and both fluid and particle inertia, are discussed. In passive microrheology experiments, on the other hand, the position of a thermally-uctuating probe is tracked and analyzed to determine its diffusivity.